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Chapter 57 — Eczema, Psoriasis, Cutaneous Infections, Acne, and Other Common Skin Disorders

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1. Eczema (Dermatitis)

Atopic Dermatitis (AD)

• Epidemiology: Most common chronic inflammatory skin disease; onset usually in childhood; strong association with asthma, allergic rhinitis, and food allergies (atopic triad).
• Pathogenesis: Th2-skewed immune response, defective skin barrier (filaggrin mutations), IgE elevation. IL-4, IL-13, and IL-31 are key cytokines.
• Clinical features:
  • Infants: face, scalp, extensor surfaces
  • Children/adults: flexural areas (antecubital and popliteal fossae), neck
  • Lichenification, prurigo nodules in chronic disease
• Diagnosis: Clinical (Hanifin-Rajka criteria)
• Management:
  • Emollients (cornerstone of therapy)
  • Topical corticosteroids (first-line)
  • Topical calcineurin inhibitors (tacrolimus, pimecrolimus) — steroid-sparing
  • Dupilumab (anti-IL-4Rα) — FDA-approved for moderate-severe AD
  • Oral antihistamines for pruritus
  • Bleach baths to reduce S. aureus colonization

Contact Dermatitis

• Diagnosis: Patch testing for ACD
• Treatment: Identify/avoid trigger; topical corticosteroids; systemic corticosteroids for severe/widespread ACD

Seborrheic Dermatitis

• Greasy, yellowish scales on erythematous base in sebum-rich areas (scalp, nasolabial folds, eyebrows, central chest)
• Associated with Malassezia (lipophilic yeast) overgrowth
• In adults: dandruff; in infants: "cradle cap"
• Treatment: Antifungal shampoos (ketoconazole, selenium sulfide, zinc pyrithione); topical corticosteroids; topical calcineurin inhibitors

Dyshidrotic Eczema (Pompholyx)

• Vesicles on lateral fingers, palms, soles
• Triggers: stress, hyperhidrosis, metals
• Treatment: topical steroids, potassium permanganate soaks

Nummular Eczema

• Coin-shaped, pruritic, crusted plaques; common in elderly and dry climates
• Treatment: topical steroids, emollients

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2. Psoriasis

• Prevalence: ~2% of the population worldwide; chronic, immune-mediated
• Pathogenesis: Th17/IL-17 and Th1/TNF-driven keratinocyte hyperproliferation; epidermal turnover ↑ (3–4 days vs. normal 28 days); HLA-Cw6 association
• Triggers: Stress, streptococcal infection (guttate), trauma (Koebner phenomenon), medications (lithium, beta-blockers, antimalarials, NSAIDs), HIV

Clinical Forms

Auspitz Sign

Management

• Corticosteroids
• Vitamin D analogues (calcipotriol)
• Retinoids (tazarotene)
• Calcineurin inhibitors (facial/intertriginous)

• Narrowband UVB (nbUVB) — preferred
• PUVA (psoralen + UVA)

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3. Cutaneous Infections

Bacterial

Fungal

Viral

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4. Acne Vulgaris

• Pathogenesis: Four key factors — follicular hyperkeratosis, excess sebum, Cutibacterium acnes (formerly Propionibacterium acnes) colonization, inflammation
• Triggers: Androgens, occlusion, certain medications (steroids, lithium), cosmetics

Clinical Forms

Management (Stepwise)

Isotretinoin: Highly teratogenic (iPLEDGE program required); monitor triglycerides, LFTs; causes mucocutaneous dryness.

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5. Rosacea

• Chronic facial condition: erythema, telangiectasias, papulopustules (no comedones), phymatous changes (rhinophyma), ocular rosacea
• Triggers: heat, sun, alcohol, spicy food, Demodex mites
• Management:
  • Topical metronidazole, azelaic acid, ivermectin
  • Oral doxycycline (sub-antimicrobial doses)
  • Laser for telangiectasias; isotretinoin for severe phymatous disease

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6. Other Common Disorders

Urticaria (Hives)

• Transient, pruritic wheals; angioedema may accompany
• Acute (<6 weeks): usually allergic/infectious; Chronic (>6 weeks): autoimmune or idiopathic
• Treatment: non-sedating antihistamines (cetirizine, loratadine); omalizumab for refractory chronic urticaria

Pityriasis Rosea

• Herald patch → widespread "Christmas tree" distribution on trunk
• Self-limiting (6–8 weeks); etiology linked to HHV-6/7
• Treatment: symptomatic; oral erythromycin or acyclovir may shorten course

Lichen Planus

• Pruritic, polygonal, purple, planar papules (6 P's); lacy white Wickham's striae in oral mucosa
• May be drug-induced (thiazides, antimalarials, beta-blockers)
• Treatment: topical/systemic corticosteroids; topical retinoids

Acanthosis Nigricans

• Velvety, hyperpigmented thickening in flexures (neck, axillae, groin)
• Strong association with insulin resistance, type 2 diabetes, obesity, internal malignancy (especially gastric adenocarcinoma when extensive/rapid onset)

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Key Takeaways

• Eczema = impaired barrier + Th2 inflammation; dupilumab is transformative for moderate-severe AD
• Psoriasis = Th17-driven; biologic therapies (anti-IL-17, anti-IL-23) offer near-complete clearance
• Acne = isotretinoin is the most effective agent for severe disease; always counsel on teratogenicity
• Cutaneous infections require identifying organism type (bacterial/fungal/viral) to direct targeted therapy
• Common skin disorders frequently signal systemic disease (acanthosis nigricans → insulin resistance; extensive psoriasis → consider HIV)

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Classification of Papulosquamous, Bullous, and Other Skin Disorders

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I. PAPULOSQUAMOUS SKIN DISORDERS

A. Primary Cutaneous Disorders

1. Psoriasis — widespread/resistant disease may indicate HIV infection
2. Tinea (dermatophytosis) — widespread disease may indicate immunosuppression
3. Pityriasis rosea
4. Lichen planus
5. Parapsoriasis
   • Small plaque parapsoriasis
   • Large plaque parapsoriasis
6. Bowen's disease (squamous cell carcinoma in situ)
7. Lichen simplex chronicus
8. Seborrheic dermatitis
9. Pityriasis rubra pilaris
10. Ichthyosis vulgaris

B. Drug-Induced

1. Drug-induced papulosquamous eruptions (lithium, beta-blockers, antimalarials, gold, NSAIDs)

C. Systemic Diseases

1. Lupus erythematosus — primarily subacute or chronic (discoid) lesions
2. Cutaneous T-cell lymphoma (CTCL) — in particular, mycosis fungoides
3. Secondary syphilis
4. Reactive arthritis (formerly Reiter's syndrome) — keratoderma blennorrhagica
5. Sarcoidosis — with scale less common than without scale
6. Bazex syndrome (acrokeratosis paraneoplastica)

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II. BULLOUS (VESICULOBULLOUS) SKIN DISORDERS

A. Primary Cutaneous Disorders

Intraepidermal (Suprabasal / Subcorneal)

1. Pemphigus vulgaris — suprabasal split; anti-desmoglein 1 & 3 IgG
2. Pemphigus foliaceus — subcorneal split; anti-desmoglein 1 IgG
3. Pemphigus erythematosus (localized form of pemphigus foliaceus)
4. Pemphigus vegetans
5. IgA pemphigus
6. Paraneoplastic pemphigus

Subepidermal

1. Bullous pemphigoid — most common autoimmune blistering disease; anti-BP180 & BP230 IgG; affects elderly
2. Mucous membrane pemphigoid (cicatricial pemphigoid) — anti-BP180, laminin-332
3. Pemphigoid gestationis (herpes gestationis) — pregnancy-associated
4. Dermatitis herpetiformis — IgA deposits at dermal papillae; associated with celiac disease; anti-endomysial/tissue transglutaminase antibodies
5. Linear IgA bullous dermatosis (LABD) — IgA at BMZ; drug-induced (vancomycin) or idiopathic
6. Epidermolysis bullosa acquisita (EBA) — anti-type VII collagen
7. Anti-p200 pemphigoid

Genetic/Inherited

1. Epidermolysis bullosa (EB) — simplex, junctional, dystrophic subtypes

Infectious

1. Bullous impetigo — S. aureus (exfoliative toxin)
2. Staphylococcal scalded skin syndrome (SSSS)
3. Herpes simplex — grouped vesicles
4. Varicella-zoster / Herpes zoster — dermatomal vesicles
5. Hand-foot-mouth disease — Coxsackievirus A16

Contact/Irritant

1. Bullous contact dermatitis (e.g., poison ivy, strong irritants)

B. Systemic Diseases Causing Bullae

1. Porphyria cutanea tarda — photodistributed bullae on dorsal hands; uroporphyrinogen decarboxylase deficiency
2. Diabetic bullae (bullosis diabeticorum)
3. Systemic lupus erythematosus — bullous LE (anti-type VII collagen)
4. Erythema multiforme — targetoid lesions ± bullae; HSV or drug-triggered
5. Stevens-Johnson syndrome (SJS) — <10% BSA epidermal detachment; drug-induced
6. Toxic epidermal necrolysis (TEN) — >30% BSA; full-thickness epidermal necrosis; drug-induced

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III. OTHER NOTABLE DISORDER CLASSIFICATIONS (Harrison's Framework)

A. Eczematous Disorders

1. Atopic dermatitis
2. Irritant contact dermatitis
3. Allergic contact dermatitis
4. Seborrheic dermatitis
5. Nummular eczema
6. Dyshidrotic eczema (pompholyx)
7. Stasis dermatitis

B. Pustular Disorders

1. Acne vulgaris
2. Rosacea
3. Folliculitis
4. Pustular psoriasis (localized palmoplantar / generalized von Zumbusch)
5. Disseminated gonococcal infection
6. Viral pustular eruptions

C. Urticarial/Reactive Disorders

1. Urticaria (acute and chronic)
2. Angioedema
3. Erythema multiforme
4. Erythema nodosum (panniculitis)
5. Pityriasis rosea

D. Hyperpigmented / Hypopigmented Disorders

1. Acanthosis nigricans
2. Vitiligo
3. Melasma
4. Post-inflammatory hyperpigmentation
5. Pityriasis versicolor

E. Vascular / Purpuric Disorders

1. Leukocytoclastic vasculitis
2. Henoch-Schönlein purpura
3. Livedo reticularis
4. Purpura fulminans

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Summary Table

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Metabolic Causes of Hyperpigmentation

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Full Classification Context — Diffuse Hyperpigmentation

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Metabolic Causes — Detailed

1. Porphyria Cutanea Tarda (PCT)

• Defect: Uroporphyrinogen decarboxylase deficiency → accumulation of porphyrins
• Mechanism of pigmentation: Porphyrins are photoreactive — UV light activates accumulated porphyrins → reactive oxygen species → melanocyte stimulation → hyperpigmentation
• Distribution: Sun-exposed areas (face, dorsal hands, forearms)
• Associated features: Photodistributed bullae, skin fragility, milia, hypertrichosis (especially facial)
• Associations: Hepatitis C, alcohol, estrogens, iron overload, HIV

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2. Hemochromatosis (Type 1)

• Defect: HFE gene mutation → excess iron deposition in tissues
• Mechanism: Elevated iron in the skin directly stimulates melanin pigment production by melanocytes
• Classic appearance: "Bronze diabetes" — generalised bronze/grey-brown discolouration
• Distribution: Diffuse, most prominent in sun-exposed areas, genitalia, old scars
• Associated features: Liver cirrhosis, diabetes mellitus, cardiomyopathy, hypogonadism, arthropathy

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3. Pellagra (Niacin / Nicotinic Acid Deficiency)

• Defect: Vitamin B₃ (niacin) deficiency — dietary, or secondary to:
  • Vitamin B₆ deficiency (needed for tryptophan → niacin conversion)
  • Functioning carcinoid tumors (excess tryptophan consumed for serotonin → niacin depleted)
  • Isoniazid therapy (inhibits B₆)
  • Hartnup disease (impaired tryptophan absorption)
• Mechanism: Niacin is essential for NAD/NADP redox reactions; deficiency → impaired DNA repair in UV-exposed skin → inflammatory pigmentation
• Appearance: Brown discolouration with a thin, varnish-like scale
• Distribution: Sun-exposed areas — classic "Casal's necklace" on the neck
• Classic triad: Dermatitis, Diarrhoea, Dementia ("3 Ds")

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4. Vitamin B₁₂ Deficiency

• Mechanism: B₁₂ is required for melanin synthesis regulation; deficiency → increased melanin production, possibly via decreased inhibition of tyrosinase
• Appearance: Diffuse hyperpigmentation, often accentuated on knuckles, palmar creases, oral mucosa, nail beds (longitudinal melanonychia)
• Associated features: Megaloblastic anaemia, subacute combined degeneration of the cord, glossitis

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5. Folic Acid (Folate) Deficiency

• Mechanism: Similar to B₁₂ — folate participates in one-carbon metabolism affecting melanin pathway; deficiency disrupts this balance
• Appearance: Diffuse hyperpigmentation; can mimic B₁₂ deficiency skin changes
• Associated features: Megaloblastic anaemia, neural tube defects (in pregnancy)

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6. Malabsorption Syndromes (including Whipple's Disease)

• Whipple's disease: ~50% of patients have associated hyperpigmentation
  • Caused by Tropheryma whipplei
  • Malabsorption → combined niacin, B₁₂, and folate deficiencies → pigmentation
  • Other features: diarrhoea, arthralgias, weight loss, lymphadenopathy, CNS involvement
• Other malabsorption states (Crohn's, celiac, short bowel syndrome) → nutrient deficiencies → similar pigmentary changes

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Summary Table

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Peripheral Blood Smear in Systemic Diseases

Harrison's Principles of Internal Medicine, 21st Edition — Chapter 62

"Every internist should know how to examine a peripheral blood smear." — Harrison's, p. 1714

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Why the Peripheral Blood Smear Matters

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I. RED BLOOD CELL (RBC) ABNORMALITIES

A. Size Abnormalities

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B. Shape Abnormalities (Poikilocytosis)

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C. Colour / Staining Abnormalities

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D. Inclusions Within RBCs

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II. WHITE BLOOD CELL (WBC) ABNORMALITIES

A. Quantitative Changes

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B. Morphological WBC Abnormalities

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III. PLATELET ABNORMALITIES

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IV. SYSTEMIC DISEASES — PBS Correlation Summary

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Key Teaching Points (Harrison's, p. 1714)

1. PBS is indispensable — automated analysers miss morphological detail
2. Always examine the feathered edge of the smear (optimal RBC distribution)
3. Findings in PBS must be interpreted alongside the clinical context and CBC
4. Leukoerythroblastic picture on PBS = bone marrow infiltration until proven otherwise — warrants bone marrow biopsy
5. Schistocytes on PBS in the right clinical context = haematological emergency (TTP/HUS/DIC)
6. Hypersegmented neutrophils may be the earliest finding in megaloblastic anaemia, preceding macrocytosis

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Pseudotumor Cerebri (Idiopathic Intracranial Hypertension)

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Definition & Nomenclature

The term "benign" is now discouraged because up to 25% of patients suffer permanent visual loss.

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Epidemiology

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Etiology & Risk Factors

A. Obesity & Hormonal

• Obesity — most significant modifiable risk factor (mechanism possibly related to increased intra-abdominal pressure → elevated venous pressure → impaired CSF absorption)
• Weight gain — even modest increases can precipitate IIH
• Pregnancy
• Polycystic ovarian syndrome (PCOS)

B. Drugs & Medications

C. Systemic / Metabolic Conditions

• Addison's disease (adrenal insufficiency)
• Hypoparathyroidism
• Severe anaemia (especially iron deficiency)
• Sleep apnoea
• Chronic kidney disease

D. Venous Sinus Pathology

• Cerebral venous sinus thrombosis (most important secondary cause)
• Bilateral internal jugular vein obstruction
• Superior vena cava syndrome
• Arteriovenous malformations

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Pathophysiology

1. Impaired CSF absorption at arachnoid granulations (most favoured)
2. Increased CSF production (acetazolamide lowers ICP by reducing this)
3. Venous hypertension → elevated venous sinus pressure → impaired CSF outflow → raised ICP
   • Transverse sinus stenosis is found in >90% of IIH patients (may be cause or consequence)
4. Obesity-related mechanisms: Increased intra-abdominal and intrathoracic pressure → elevated cerebral venous pressure → raised ICP; adipose tissue may also produce hormones (adipokines) that alter CSF dynamics

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Clinical Features

Symptoms

Signs

Note: Neurological examination is otherwise normal — no focal deficits, no altered consciousness, no meningism (which differentiates it from intracranial mass/meningitis)

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Diagnostic Criteria (Modified Dandy Criteria / Friedman & Jacobson 2013)

1. Signs/symptoms of raised ICP (headache, papilledema, TVOs, diplopia)
2. No other neurological abnormality (excluding CN VI palsy)
3. Neuroimaging: Normal brain parenchyma, no hydrocephalus, no mass lesion, no structural cause; MRI may show IIH-specific features (see below)
4. Normal CSF composition (cell count, protein, glucose)
5. Elevated CSF opening pressure:
   • ≥25 cmH₂O in adults (measured in lateral decubitus position)
   • ≥28 cmH₂O in children
   • 20–25 cmH₂O = borderline (requires additional supportive features)
6. No other cause identified for raised ICP

"An elevated pressure, with normal cerebrospinal fluid, points by exclusion to the diagnosis of pseudotumor cerebri." — Harrison's, p. 964

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Investigations

1. Neuroimaging (MRI Brain ± MRV)

2. Lumbar Puncture

• Must be done in lateral decubitus position (sitting position falsely elevates pressure)
• Measure opening pressure (normal <20 cmH₂O)
• Send CSF for cell count, protein, glucose, culture — will be normal in IIH
• LP is both diagnostic and temporarily therapeutic (symptom relief after CSF removal)

3. Ophthalmological Assessment

• Fundoscopy: Grade papilledema (Frisén scale 0–5)
• Visual field testing (perimetry): Humphrey visual fields — enlarged blind spot, arcuate defects
• OCT (Optical Coherence Tomography): Measures retinal nerve fibre layer (RNFL) thickness — objective monitoring of papilledema and optic nerve damage
• Visual acuity: Snellen chart

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Imaging Illustration

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Management

Step 1: Treat Underlying Cause

• Stop offending drugs (tetracyclines, retinoids, steroids)
• Treat venous sinus thrombosis if present
• Correct endocrine/metabolic disorders

Step 2: Weight Loss (Cornerstone)

• 5–10% body weight reduction significantly lowers ICP and improves symptoms
• Bariatric surgery: Indicated in patients who cannot achieve adequate weight loss through diet — highly effective (Harrison's, p. 964)

Step 3: Medical Therapy

Step 4: Repeated Lumbar Punctures

• Temporary relief; not a long-term solution
• Used in pregnancy (where medications may be limited) and acute severe cases

Step 5: Surgical Interventions

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Complications

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Special Populations

Pregnancy

• IIH may worsen due to weight gain and hormonal changes
• Acetazolamide is relatively contraindicated in first trimester (teratogenic in animals)
• Serial LP and ONSF are preferred during pregnancy
• Delivery route not affected by IIH alone

Paediatric IIH

• Prepubertal children: more equal sex ratio, less associated with obesity
• Post-pubertal adolescents: epidemiology mirrors adults (female, obese)
• Must exclude all secondary causes rigorously

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Summary Algorithm

Suspected IIH (headache + papilledema + obese young woman)
        ↓
MRI Brain + MRV → exclude mass, hydrocephalus, CVT
        ↓
Lumbar Puncture (lateral decubitus) → elevated opening pressure + normal CSF
        ↓
Ophthalmology referral → grade papilledema, visual fields, OCT
        ↓
Mild-moderate disease           Severe/rapid visual loss
        ↓                               ↓
Weight loss + Acetazolamide     Urgent shunting / ONSF / stenting
        ↓
Monitor visual fields every 1–3 months
        ↓
If no improvement → add topiramate / consider surgery

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Chapter 37 — Dyspnea

Harrison's Principles of Internal Medicine, 21st Edition

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Definition

Dyspnea differs from tachypnea (increased respiratory rate) and hyperpnea (increased ventilation) — it is fundamentally a subjective perception, not an objective measurement.

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Pathophysiology

Neural Framework — Afferent Signals

1. Chemoreceptors

2. Mechanoreceptors

3. Additional Afferent Sources

• Pulmonary vascular receptors: Respond to changes in pulmonary artery pressure
• Skeletal muscle metaboreceptors: Activated during exercise; contribute to exertional dyspnea
• Upper airway receptors: Cold air, irritants → modify dyspnea perception

4. Efferent–Afferent Mismatch ("Neuromechanical Dissociation")

• Neuromuscular weakness (high drive, low output)
• Severe airflow obstruction (high drive, high resistance)
• Reduced lung compliance (high drive, stiff lungs)

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Qualitative Descriptors of Dyspnea

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Etiology — Causes of Dyspnea

Acute Dyspnea (minutes to hours)

Chronic / Subacute Dyspnea (weeks to months)

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Measurement & Grading

MRC (Medical Research Council) Dyspnea Scale

Modified Borg Scale

• 0 (nothing at all) to 10 (maximal) — used during exercise testing and inpatient assessment

NYHA Classification (for Cardiac Dyspnea)

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Clinical Evaluation

History — Key Questions

Positions and Dyspnea

Physical Examination

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Diagnostic Approach (Harrison's, p. 1112)

"As many as two-thirds of patients will require diagnostic testing beyond the initial clinical presentation."

Initial Investigations (First-line for all)

Second-line Investigations

Algorithmic Approach

Dyspnea
    ↓
Acute or Chronic?
    ↓                           ↓
ACUTE                         CHRONIC
History + Exam                History + Exam
Pulse oximetry, CXR, ECG      CXR, ECG, CBC, BNP, PFTs
BNP, ABG, troponin            Echocardiogram if cardiac
    ↓                              ↓
Life-threatening first:        Still unclear?
Pneumothorax → chest drain         ↓
Pulmonary oedema → diuretics    CPET / HRCT / CTPA /
Severe asthma → bronchodilators  Subspecialty referral
PE → anticoagulation
Tamponade → pericardiocentesis

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Management

Disease-Specific Treatment

Symptomatic / Palliative Management of Dyspnea

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Special Situations

Dyspnea in the Absence of Hypoxaemia

• Common in anaemia, deconditioning, pulmonary hypertension (may maintain saturation until late)
• Normal SpO₂ does not exclude significant dyspnea or serious pathology

Dyspnea with Normal PFTs and Normal Imaging

1. Cardiac cause (exercise echocardiography or CPET)
2. Pulmonary hypertension (right heart catheterisation)
3. Deconditioning
4. Psychogenic / functional dyspnea
5. Neuromuscular disease (maximal inspiratory/expiratory pressure measurements)

Dyspnea at End of Life

• Opioids remain the cornerstone of palliation
• Oxygen helpful only if hypoxaemic
• Fan therapy, cool room, upright positioning
• Avoid futile investigations — focus on comfort

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Key Teaching Points (Harrison's, Ch. 37)

1. Dyspnea is multidimensional — its quality (air hunger vs. tightness vs. effort) guides diagnosis
2. The efferent–afferent mismatch model best explains dyspnea across conditions
3. BNP is the single most useful initial biomarker to differentiate cardiac from pulmonary dyspnea
4. CPET is the gold standard when aetiology remains unclear after standard workup
5. Orthopnoea and PND are highly specific for heart failure
6. In normoxaemic patients, supplemental oxygen does not relieve dyspnea — cool facial airflow (fan) is more effective
7. Low-dose opioids are the most evidence-based pharmacological treatment for refractory/palliative dyspnea
8. For patients with known cardiopulmonary disease, always ask: has the known disease progressed, or is there a new process? (Harrison's, p. 1112)

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Harrison's Chapters 13–66: Cardinal Manifestations — Brief Summaries

Harrison's Principles of Internal Medicine, 21st Edition

Part 2: Cardinal Manifestations and Presentation of Diseases

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SECTION 1 — PAIN

Ch. 13 — Pain: Pathophysiology and Management

• Pain = unpleasant sensory/emotional experience from actual or potential tissue damage
• Types: Nociceptive (somatic/visceral), neuropathic, nociplastic
• Transduction → Transmission → Modulation → Perception (4-step pathway)
• Key receptors: Aδ (sharp, fast) and C fibres (burning, slow); first synapse in dorsal horn
• Sensitisation: Peripheral (↑ prostaglandins, bradykinin) and central (wind-up, allodynia)
• Descending modulation: Endogenous opioids, serotonin, noradrenaline pathways
• WHO analgesic ladder: Paracetamol/NSAIDs → weak opioids → strong opioids; adjuvants at each step
• Neuropathic pain: TCAs, SNRIs, gabapentinoids, topical lidocaine

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Ch. 14 — Chest Discomfort

• Most critical diagnosis to exclude: ACS (STEMI/NSTEMI/UA)
• Causes classified by structure:

• Ischaemic pain: pressure/squeezing, radiation to jaw/left arm, associated diaphoresis
• Key tools: ECG, troponin, CXR; HEART score for risk stratification

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Ch. 15 — Abdominal Pain

• Visceral pain: poorly localised, midline, cramping (hollow organs) or aching (solid organs)
• Parietal pain: well-localised, sharp, worsened by movement → peritoneal irritation
• Referred pain: diaphragmatic irritation → shoulder tip; ureteric colic → groin
• Causes by quadrant:
  • RUQ: cholecystitis, hepatitis, Fitz-Hugh-Curtis
  • LUQ: splenomegaly, gastritis, pancreatitis (tail)
  • RLQ: appendicitis, Meckel's, ovarian pathology, Crohn's
  • LLQ: diverticulitis, sigmoid volvulus, ovarian cyst
  • Diffuse: peritonitis, mesenteric ischaemia, IBD, IBS
• Surgical emergencies: Perforated viscus, acute mesenteric ischaemia, ruptured ectopic, aortic aneurysm

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Ch. 16 — Headache

• Most common: Tension-type (bilateral, band-like, no nausea)
• Migraine: Unilateral, pulsating, nausea/vomiting, photo/phonophobia; with or without aura; Tx: triptans, CGRP antagonists
• Cluster: Periorbital, autonomic features (lacrimation, ptosis, rhinorrhoea), circadian; Tx: O₂, sumatriptan
• Secondary causes (red flags — SNOOP4):
  • Systemic illness, Neurological deficit, Onset sudden/thunderclap, Older age, Positional, Progressive, Papilledema, Prior headache change
• Thunderclap: SAH until proven otherwise → CT head → LP if CT negative
• Raised ICP: Progressive, worse in morning, with Valsalva, papilledema

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Ch. 17 — Back and Neck Pain

• Most common: Non-specific mechanical low back pain (95%)
• Red flags for serious cause (TUMOUR/FRACTURE):
  • Age >50, history of cancer, unexplained weight loss, night pain, fever, bowel/bladder dysfunction, saddle anaesthesia
• Lumbar disc herniation: L4-L5 (foot drop), L5-S1 (↓ ankle reflex, calf weakness)
• Spinal stenosis: Neurogenic claudication — bilateral leg pain with walking, relieved by flexion
• Cauda equina syndrome: Surgical emergency — saddle anaesthesia + urinary retention
• Cervical myelopathy: Upper motor neuron signs in legs + lower motor neuron signs at level of lesion
• Investigations: MRI spine (first-line for neurological deficit or red flags)

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Ch. 18 — Numbness, Tingling, and Sensory Loss

• Sensory modalities: Pain/temperature (spinothalamic — contralateral) vs. vibration/proprioception (dorsal columns — ipsilateral)
• Peripheral neuropathy: Glove-and-stocking distribution; diabetes, alcohol, B₁₂ deficiency, Guillain-Barré
• Mononeuropathy: Single nerve compression (carpal tunnel, ulnar, common peroneal)
• Spinal cord lesions: Brown-Séquard (hemisection), complete transection, central cord syndrome
• Thalamic lesions: Contralateral hemibody sensory loss
• Cortical lesions: Contralateral limb; discriminative sensation most affected

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Ch. 19 — Weakness and Paralysis

• Distinguish UMN vs LMN vs. NMJ vs. Muscle:

• NMJ: Fatigable weakness (myasthenia gravis — ocular, bulbar); Lambert-Eaton (proximal, ↑ with repetition)
• Myopathy: Proximal symmetric weakness, normal sensation, ↑CK
• Causes of acute paralysis: Stroke, GBS, spinal cord compression, hypokalemia, botulism

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Ch. 20 — Faintness, Syncope, Dizziness, and Vertigo

• Syncope: Transient loss of consciousness from global cerebral hypoperfusion; self-limited
  • Reflex (vasovagal — most common), orthostatic, cardiac (arrhythmia, structural)
  • Dangerous: VT, complete heart block, HOCM, aortic stenosis, PE
  • Tilt-table test, ECG, Holter monitor, echocardiogram
• Presyncope: Same causes; incomplete episode
• Dizziness: Vertigo (illusion of motion), disequilibrium, lightheadedness
• Vertigo:
  • Peripheral: BPPV (most common — Dix-Hallpike +ve, brief, fatigable), Ménière's disease (tinnitus + hearing loss + episodic vertigo), vestibular neuritis (prolonged, viral)
  • Central: Brainstem/cerebellar; no latency, non-fatigable; HINTS exam
  • BPPV treatment: Epley manoeuvre

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Ch. 21 — Syncope

• Reflex syncope: Vasovagal, situational (cough, micturition), carotid sinus hypersensitivity
• Orthostatic hypotension: ≥20 mmHg systolic drop on standing; autonomic neuropathy, hypovolaemia, drugs
• Cardiac syncope: Most dangerous — arrhythmia (prolonged QT, Brugada, WPW), structural (AS, HCM, PE)
• ROSE/SFSR/San Francisco Syncope Rules: Identify high-risk patients requiring admission
• Investigations: ECG (all), echocardiogram, Holter/implantable loop recorder, tilt table

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SECTION 2 — ALTERATIONS IN BODY TEMPERATURE

Ch. 22 — Fever

• Fever = Tcore >38°C (100.4°F); hyperpyrexia >41.5°C
• Pyrogens: Exogenous (LPS) → macrophages → endogenous pyrogens (IL-1, IL-6, TNF) → hypothalamus → PGE₂ → ↑ set-point
• Fever vs. hyperthermia: Fever = raised set-point (responds to antipyretics); Hyperthermia = failure of thermoregulation (does NOT respond — heat stroke, malignant hyperthermia, NMS)
• Causes: Infection (most common), malignancy, autoimmune/inflammatory, drugs, endocrine (thyroid storm, phaeochromocytoma)
• FUO (Fever of Unknown Origin): >38.3°C on ≥3 occasions over ≥3 weeks with no diagnosis after 1 week of investigation
  • Classic FUO causes: Infection (TB, endocarditis, abscess), malignancy (lymphoma), connective tissue disease (SLE, Still's)
• Antipyretics: Paracetamol, NSAIDs (COX-inhibitors → ↓ PGE₂)

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Ch. 23 — Fever and Rash

• Combination of fever + rash narrows differential significantly:

• Meningococcaemia: Non-blanching petechiae/purpura → emergency — immediate IV benzylpenicillin
• RMSF: Centripetal spread of petechiae (wrist/ankles → trunk); Rickettsia rickettsii; Tx: doxycycline

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Ch. 24 — Hypothermia and Frostbite

• Hypothermia: Core temp <35°C
  • Mild (32–35°C): Shivering, confusion
  • Moderate (28–32°C): ↓ shivering, arrhythmias (J/Osborn waves on ECG), hypotension
  • Severe (<28°C): VF risk, no shivering, coma
  • Rewarming: Passive (mild) → active external (moderate) → active internal (severe: warmed IV fluids, bladder/peritoneal lavage, ECMO in refractory VF)
  • "Not dead until warm and dead"
• Frostbite: Ice crystal formation in tissues; superficial vs. deep; Tx: rapid rewarming in 40°C water, ibuprofen, TPA for severe cases

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SECTION 3 — NERVOUS SYSTEM DYSFUNCTION

Ch. 25 — Confusion and Delirium

• Delirium: Acute disturbance of attention + cognition with fluctuating course; reversible
• Hyperactive (agitation, hallucinations) vs. Hypoactive (withdrawn, quiet — often missed) vs. Mixed
• Causes — AEIOU TIPS: Alcohol/drugs, Epilepsy, Infection, Overdose, Uraemia, Trauma, Insulin (hypo/hyperglycaemia), Psychiatric, Stroke/structural
• Predisposing (baseline vulnerability): Age, dementia, sensory impairment, dehydration
• Precipitating: Infection, surgery, medications (anticholinergics, opioids, benzodiazepines), sleep deprivation
• CAM (Confusion Assessment Method): Acute onset + inattention + (disorganised thinking OR altered consciousness)
• Management: Treat cause; non-pharmacological first (reorientation, day/night cues, avoid restraints); haloperidol if agitated and dangerous

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Ch. 26 — Dementia

• Progressive cognitive decline affecting ≥2 domains; interferes with daily function
• Alzheimer's disease (most common, 60–70%): β-amyloid plaques, neurofibrillary tangles; episodic memory first; MMSE/MoCA; Tx: cholinesterase inhibitors (donepezil), memantine
• Vascular dementia: Stepwise decline; risk factors = stroke risk factors; neuroimaging shows infarcts
• Lewy body dementia: Fluctuating cognition, visual hallucinations, parkinsonism, REM sleep behaviour disorder; hypersensitive to antipsychotics
• Frontotemporal dementia (FTD): Behavioural changes or language dysfunction; younger onset; tau/TDP-43 pathology
• Reversible causes (must exclude): B₁₂ deficiency, hypothyroidism, neurosyphilis, normal pressure hydrocephalus (NPH — triad: dementia, gait apraxia, urinary incontinence), subdural haematoma, depression (pseudodementia)

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Ch. 27 — Aphasia, Memory Loss, and Other Focal Cerebral Disorders

• Aphasia:
  • Broca's (expressive): Non-fluent, good comprehension, poor repetition; frontal lobe
  • Wernicke's (receptive): Fluent but paraphasic, poor comprehension; temporal lobe
  • Global: Both expression and comprehension impaired; large MCA territory infarct
  • Conduction: Good fluency + comprehension, poor repetition; arcuate fasciculus
• Memory: Declarative (hippocampus) vs. procedural (basal ganglia/cerebellum)
• Amnesia: Anterograde (can't form new memories) vs. retrograde (can't recall past)
• Neglect: Non-dominant parietal lobe; inattention to contralateral space
• Apraxia: Inability to perform learned motor acts despite intact motor/sensory function
• Agnosia: Inability to recognise objects despite intact sensory function

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Ch. 28 — Sleep Disorders

• Sleep stages: NREM (N1→N2→N3/slow wave) + REM; ~90 min cycles
• Insomnia: Most common; acute (stress) or chronic (>3 months); CBT-I first-line over pharmacotherapy
• Obstructive sleep apnoea (OSA): Repetitive upper airway collapse; snoring, apnoeas, EDS; AHI ≥5; CPAP is gold standard; associated with HTN, AF, metabolic syndrome
• Narcolepsy: Excessive daytime sleepiness + cataplexy (type 1); hypocretin/orexin deficiency; Tx: modafinil (EDS), sodium oxybate (cataplexy)
• Restless legs syndrome (RLS): Urge to move legs at rest, worse at night, relieved by movement; dopaminergic deficiency; Fe deficiency; Tx: dopamine agonists (pramipexole), gabapentin
• Circadian rhythm disorders: Jet lag, shift work, delayed sleep phase syndrome
• Parasomnias: Sleepwalking, REM sleep behaviour disorder (RBD — acts out dreams; early marker of Parkinson's/Lewy body dementia)

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SECTION 4 — DISORDERS OF EYES, EARS, NOSE, AND THROAT

Ch. 29 — Disorders of the Eye

• Visual loss:
  • Sudden painless monocular: CRAO (cherry red spot), CRVO, anterior ischaemic optic neuropathy (AION), vitreous haemorrhage, retinal detachment
  • Sudden painful: Acute angle-closure glaucoma (fixed mid-dilated pupil, hard eye, corneal oedema)
  • Transient monocular (amaurosis fugax): TIA/carotid disease — treat as stroke
  • Bilateral: Cortical blindness (occipital stroke), raised ICP, toxic (methanol)
• Afferent pupillary defect (RAPD/Marcus Gunn): Optic nerve or severe retinal disease
• Papilledema: Bilateral disc swelling from raised ICP; visual obscurations; must urgently investigate
• Diplopia: Monocular (refractive) vs. binocular (CN III, IV, VI palsy or NMJ)
  • CN III palsy: "Down and out" + ptosis ± dilated pupil (surgical CN III — posterior communicating artery aneurysm)
• Glaucoma: Optic nerve damage from raised IOP; open angle (chronic, asymptomatic) vs. closed angle (acute, emergency); Tx: topical beta-blockers, prostaglandin analogues

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Ch. 30 — Disorders of Smell, Taste, and Hearing

• Anosmia: Post-viral (COVID-19), head trauma (cribriform plate), nasal polyps, neurodegenerative (Parkinson's — early sign), tumour (olfactory groove meningioma)
• Dysgeusia/Ageusia: Zinc deficiency, B₁₂ deficiency, post-viral, medication side effect
• Hearing loss:
  • Conductive: Outer/middle ear; Rinne (BC>AC), Weber lateralises to affected side; causes: wax, otitis media, otosclerosis
  • Sensorineural: Cochlea/VIII nerve; Rinne (AC>BC), Weber lateralises to better ear; causes: presbycusis (ageing), noise-induced, Ménière's, acoustic neuroma, ototoxic drugs (aminoglycosides, cisplatin, loop diuretics)
• Tinnitus: Subjective vs. objective (vascular — AVM, glomus tumour); pulsatile tinnitus in IIH
• Vertigo: See Ch. 20

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SECTION 5 — CARDIOVASCULAR SYMPTOMS

Ch. 31 — Palpitations

• Awareness of heartbeat; may represent benign or life-threatening arrhythmia
• Characterise: Regular vs. irregular; onset/offset (sudden = re-entry); triggers; associated presyncope/syncope
• Causes: Ectopics (most common — PACs/PVCs), SVT, AF/flutter, VT, anxiety, hyperthyroidism, anaemia, caffeine, drugs
• Key investigations: 12-lead ECG (during symptoms if possible), Holter monitor (24–48h), event recorder, implantable loop recorder (for infrequent symptoms); TFTs, FBC, electrolytes
• Red flags: Palpitations + syncope + family history of sudden death = urgent cardiology referral

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Ch. 32 — Hypertension

• Definition: ≥130/80 mmHg (ACC/AHA 2017) or ≥140/90 (ESC/WHO)
• Primary (essential): 90–95%; no identifiable cause; multifactorial (genetics, RAAS, SNS, salt)
• Secondary causes (5–10%): Renal artery stenosis, primary hyperaldosteronism (Conn's), phaeochromocytoma, Cushing's, coarctation of aorta, OSA, CKD
• Hypertensive urgency: Severe HTN without end-organ damage → oral agents
• Hypertensive emergency: Severe HTN + end-organ damage (hypertensive encephalopathy, aortic dissection, eclampsia, acute MI, acute HF) → IV agents (labetalol, nicardipine, nitroprusside)
• Treatment: Lifestyle → thiazides, ACE inhibitors/ARBs, CCBs, beta-blockers (compelling indications)
• JNC/ESC stages: Stage 1 (130–139/80–89) → Stage 2 (≥140/≥90)

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Ch. 33 — Cardiac Arrest and Sudden Cardiac Death

• SCD: Unexpected cardiac death within 1h of symptom onset; most common cause = VF from CAD
• Causes: Structural (CAD, HCM, ARVC, dilated CM) vs. Primary electrical (long QT, Brugada, WPW, CPVT)
• BLS → ACLS: Chest compressions (100-120/min, 5-6cm depth) → defibrillation (shockable: VF/pVT) → adrenaline (1mg IV q3-5min) → amiodarone
• Post-ROSC: Targeted temperature management (32-36°C for 24h), PCI if STEMI/suspected cardiac cause, neuroprognostication at 72h
• Prevention: ICD in high-risk patients (EF ≤35%, sustained VT, survivors of SCD)

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Ch. 34 — Shock

• Definition: Inadequate tissue perfusion and oxygen delivery; MAP <65 mmHg with end-organ dysfunction
• 4 types:

• Septic shock: Sepsis + vasopressors + lactate >2 despite fluid resuscitation; Tx: 30 mL/kg crystalloid, noradrenaline (first-line vasopressor), hydrocortisone if refractory, antibiotics within 1h
• Distributive: Beck's triad (tamponade) → pericardiocentesis

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Ch. 35 — Dyspnea (see Ch. 37)

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Ch. 36 — Cough and Haemoptysis

• Cough: Most common cause of chronic cough = upper airway cough syndrome (UACS/PND), asthma, GERD (the triad)
• ACE inhibitor-induced cough (bradykinin → switch to ARB)
• Acute: Viral URTI; Subacute (3–8 weeks): Post-infectious, pertussis; Chronic (>8 weeks): UACS, asthma, GERD, ILD, bronchiectasis, malignancy, TB
• Red flags: Haemoptysis, weight loss, smoker >40 yrs, new cough → CXR/CT
• Haemoptysis:
  • Causes: Bronchitis (most common), bronchogenic carcinoma, TB, bronchiectasis, PE, AVM, mitral stenosis, coagulopathy
  • Massive haemoptysis (>200–600 mL/24h): Life-threatening → airway protection, bronchoscopy, bronchial artery embolisation

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Ch. 37 — Dyspnea (Full summary covered above)

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Ch. 38 — Hypoxia and Cyanosis

• Hypoxia: Inadequate O₂ delivery to tissues
  • Hypoxaemic (↓PaO₂): Low FiO₂, hypoventilation, V/Q mismatch, shunt, diffusion impairment
  • Anaemic: Normal PaO₂, ↓Hb carrying capacity
  • Stagnant/circulatory: Normal PaO₂ + Hb, ↓CO (heart failure, shock)
  • Histotoxic: Normal delivery, impaired utilisation (cyanide poisoning)
• A-a gradient: Normal <15 mmHg; elevated in V/Q mismatch, shunt, diffusion; normal in hypoventilation/altitude
• Cyanosis:
  • Central: Low SaO₂; tongue + mucous membranes involved; causes = severe lung disease, R→L shunt, methaemoglobinaemia
  • Peripheral: Normal SaO₂, ↑O₂ extraction; cold, ↓CO, Raynaud's; spares mucous membranes
• Methaemoglobinaemia: Chocolate-brown blood; saturation gap; Tx: methylene blue

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Ch. 39 — Oedema

• Oedema = excess interstitial fluid; clinically apparent when >3L accumulated
• Starling forces: ↑ capillary hydrostatic pressure OR ↓ oncotic pressure → oedema
• Generalised (anasarca):
  • Cardiac: Dependent, pitting; JVP ↑, S3, orthopnoea
  • Renal (nephrotic): Periorbital (morning), pitting; heavy proteinuria >3.5g/day; ↓albumin
  • Hepatic (cirrhosis): Ascites prominent; ↓albumin, ↑portal pressure; spider naevi, palmar erythema
  • Nutritional/Kwashiorkor: ↓albumin from malnutrition
  • Myxoedema: Non-pitting, hypothyroidism; periorbital; no protein loss
• Localised oedema: DVT, cellulitis, lymphoedema (non-pitting), venous insufficiency
• Idiopathic oedema: Young women; exacerbated by upright posture

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Ch. 40 — Atlas of ECG

• Systematic ECG reading: Rate → Rhythm → Axis → P wave → PR interval → QRS → ST segment → T wave → QTc
• Key abnormalities:
  • STEMI: ST elevation in anatomical territories; reciprocal changes
  • LBBB: Broad notched R in V5/V6, deep S in V1; blocks STEMI diagnosis (Sgarbossa criteria)
  • LVH: Sokolow-Lyon (S in V1 + R in V5/V6 >35mm)
  • Long QT: QTc >440ms (men), >460ms (women); risk of TdP
  • Brugada: Coved ST elevation in V1-V2; risk of VF
  • WPW: Short PR, delta wave, broad QRS

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SECTION 6 — ALTERATIONS IN GASTROINTESTINAL FUNCTION

Ch. 41 — Nausea, Vomiting, and Indigestion

• Nausea/Vomiting: Mediated via vomiting centre (medullary) + chemoreceptor trigger zone (CTZ, area postrema — outside BBB)
• Causes: GI (gastroenteritis, obstruction, gastroparesis), CNS (raised ICP, migraine, motion sickness), metabolic (DKA, uraemia, Addison's), drugs (opioids, chemotherapy), pregnancy (hCG)
• Projectile vomiting: Pyloric stenosis (infant), raised ICP
• Antiemetics: Ondansetron (5-HT₃), metoclopramide (D₂), domperidone (D₂ — peripheral), prochlorperazine, dexamethasone (chemo), cyclizine (motion sickness, pregnancy)
• Indigestion/dyspepsia: Upper abdominal discomfort; functional vs. organic; investigate if alarm features (weight loss, dysphagia, haematemesis, age >55)

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Ch. 42 — Dysphagia

• Oropharyngeal (transfer): Difficulty initiating swallow; neuromuscular causes (stroke, MG, motor neuron disease, Parkinson's); nasal regurgitation, aspiration
• Oesophageal: Food "sticks" after swallowing; structural (stricture, carcinoma, ring/web) or motility (achalasia, diffuse oesophageal spasm)
• Achalasia: ↓ lower oesophageal sphincter relaxation + absent peristalsis; "bird's beak" on barium; manometry gold standard; Tx: pneumatic dilatation, Heller myotomy, POEM, botulinum toxin
• Oesophageal carcinoma: Dysphagia to solids then liquids; progressive weight loss; SCC (upper/mid) vs. adenocarcinoma (lower/GOJ — Barrett's oesophagus)
• Plummer-Vinson syndrome: Post-cricoid web + iron deficiency anaemia + dysphagia; risk of pharyngeal carcinoma

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Ch. 43 — Diarrhoea and Constipation

• Acute diarrhoea (<4 weeks): Usually infectious; secretory (watery, persists with fasting), inflammatory (bloody, fever, PMNs)
  • Non-inflammatory: Vibrio cholerae, ETEC, viruses
  • Inflammatory: Salmonella, Shigella, Campylobacter, C. difficile, EHEC (O157:H7 — HUS risk)
• Chronic diarrhoea (>4 weeks):
  • Osmotic: Stops with fasting (lactose intolerance, Mg²⁺, sorbitol)
  • Secretory: Persists with fasting (VIPoma, carcinoid, bile acid malabsorption, microscopic colitis)
  • Inflammatory: IBD (Crohn's, UC), coeliac
  • Malabsorptive: Steatorrhoea; coeliac, chronic pancreatitis, small bowel bacterial overgrowth
  • Motility: IBS, hyperthyroidism, diabetic enteropathy
• Constipation: <3 stools/week; primary (functional, slow transit, dyssynergia) vs. secondary (hypothyroidism, hypercalcaemia, drugs — opioids, antacids, CCBs)

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Ch. 44 — Weight Loss

• Involuntary weight loss >5% in 6–12 months = clinically significant; always warrants investigation
• Causes:
  • Inadequate intake: Depression, dementia, dysphagia, anorexia (cancer, drugs, social)
  • ↑ Caloric need: Hyperthyroidism, malignancy, infection (TB, HIV), COPD, heart failure
  • Malabsorption: Coeliac, IBD, pancreatic insufficiency, short bowel
• Malignancy is found in ~25% of patients with unexplained weight loss after full workup
• Investigations: CBC, CMP, TFTs, glucose, CXR, FOBT, PSA (men), mammography; CT chest/abdomen if high suspicion
• Cachexia: Weight loss + muscle wasting in context of chronic illness (cancer, HF, CKD, COPD); mediated by TNF, IL-1, IL-6

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Ch. 45 — Gastrointestinal Bleeding

• Upper GI bleeding (UGIB): Source proximal to Treitz ligament; haematemesis (bright red or coffee grounds) + melaena
  • Causes: Peptic ulcer (most common), oesophageal varices, Mallory-Weiss tear, erosive gastritis, Dieulafoy lesion, angiodysplasia, malignancy
  • Rockford/Blatchford Score: Risk stratify pre-endoscopy
  • Endoscopy within 24h (12h if high-risk variceal)
  • Varices: Terlipressin, octreotide, prophylactic antibiotics (norfloxacin/ceftriaxone), endoscopic banding
  • PUD: PPI infusion (80mg bolus + 8mg/h); endoscopic haemostasis
• Lower GI bleeding (LGIB): Source distal to Treitz; haematochezia
  • Causes: Diverticulosis (most common), angiodysplasia, colitis (IBD, ischaemic, infectious), colorectal cancer, haemorrhoids, polyps
  • Colonoscopy after bowel prep; CT angiography if haemodynamically unstable

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Ch. 46 — Jaundice

• Bilirubin metabolism: Haem → unconjugated bilirubin → liver conjugation → conjugated → bile → urobilinogen
• Classification:
  • Pre-hepatic (unconjugated): Haemolysis, Gilbert's, Crigler-Najjar; urine normal, ↑LDH, ↓haptoglobin
  • Hepatic (mixed): Hepatitis (viral, alcoholic, autoimmune, drugs), cirrhosis; ↑ALT/AST
  • Post-hepatic/cholestatic (conjugated): Bile duct obstruction (stones, stricture, carcinoma, PSC, PBC); dark urine, pale stools, pruritus; ↑ALP, ↑GGT
• Gilbert's syndrome: Benign; ↑unconjugated bilirubin with fasting/stress; glucuronosyltransferase mutation; no treatment needed
• Investigations: LFTs, bilirubin fractions, hepatitis serology, ANA/ASMA/AMA, ultrasound (first-line imaging), MRCP, ERCP

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Ch. 47 — Abdominal Swelling and Ascites

• Ascites:
  • SAAG ≥1.1 g/dL (portal hypertension): Cirrhosis (75%), cardiac ascites, Budd-Chiari
  • SAAG <1.1 g/dL (non-portal hypertension): Malignancy (peritoneal carcinomatosis), TB peritonitis, nephrotic syndrome, pancreatitis
• Spontaneous bacterial peritonitis (SBP): PMN >250/mm³ in ascitic fluid; E. coli, Klebsiella; Tx: cefotaxime; prophylaxis: norfloxacin
• Hepatic hydrothorax: Transdiaphragmatic passage of ascitic fluid; right-sided pleural effusion in cirrhosis
• Hepatorenal syndrome: Functional renal failure in decompensated cirrhosis; ↑creatinine, ↓Na; Tx: terlipressin + albumin, TIPS, liver transplantation

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SECTION 7 — ALTERATIONS IN RENAL AND URINARY TRACT FUNCTION

Ch. 48 — Azotaemia and Urinary Abnormalities

• Azotaemia: ↑BUN and creatinine
  • Pre-renal: ↓GFR from ↓renal perfusion; BUN:Cr >20:1; FENa <1%; responds to fluids
  • Intrinsic renal: ATN (ischaemia/nephrotoxins — most common), GN, AIN, vascular; FENa >2%
  • Post-renal: Obstruction; bilateral or single kidney; hydronephrosis on US
• Proteinuria: Glomerular vs. tubular; >3.5g/day = nephrotic range
• Haematuria: Microscopic vs. macroscopic; glomerular (dysmorphic RBCs, casts) vs. urological (transitional cell carcinoma, stones, infection)
• Urinary casts:
  • RBC casts → glomerulonephritis
  • WBC casts → pyelonephritis/interstitial nephritis
  • Granular/muddy brown casts → ATN
  • Waxy/broad casts → chronic renal failure
  • Hyaline casts → normal/concentrated urine

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Ch. 49 — Fluid and Electrolyte Disturbances

• Hyponatraemia (<135): Assess osmolality + volume status; SIADH (euvolaemic, ↓uOsm, ↑urine Na); Tx: fluid restriction (SIADH), hypertonic saline (severe/symptomatic); correct slowly (<10 mEq/24h) to avoid osmotic demyelination syndrome (ODS)
• Hypernatraemia (>145): Almost always = free water deficit; diabetes insipidus (central vs. nephrogenic); Tx: free water replacement
• Hypokalaemia (<3.5): Muscle weakness, cramps, U waves on ECG, ileus; causes: diarrhoea, vomiting, diuretics, Conn's, alkalosis, refeeding; Tx: KCl replacement
• Hyperkalaemia (>5.5): Peaked T waves → PR prolongation → sine wave → VF; causes: AKI, Addison's, ACE inhibitors, K-sparing diuretics; Tx: calcium gluconate (membrane stabilise), insulin + glucose, sodium bicarbonate, salbutamol, kayexalate/patiromer, dialysis
• Acid-base: Metabolic acidosis (↑AG: MUDPILES; normal AG: hyperchloraemic) vs. alkalosis; respiratory acidosis/alkalosis; Winter's formula for compensation

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Ch. 50 — Acidosis and Alkalosis

• Stepwise approach: pH → primary disorder → compensation → AG → delta-delta
• Metabolic acidosis with elevated AG (MUDPILES): Methanol, Uraemia, DKA, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates
• Normal AG metabolic acidosis: Diarrhoea (GI bicarbonate loss), renal tubular acidosis (RTA), saline infusion
• Metabolic alkalosis: Vomiting, nasogastric suction, diuretics, Conn's, Bartter/Gitelman syndromes; paradoxical aciduria in severe hypovolaemia
• Lactic acidosis: Type A (tissue hypoperfusion — sepsis, shock) vs. Type B (no hypoperfusion — metformin, liver failure, malignancy)
• Respiratory acidosis: Hypoventilation; COPD, obesity hypoventilation, sedation → ↑PCO₂
• Respiratory alkalosis: Hyperventilation; anxiety, PE, salicylates, altitude, liver failure

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SECTION 8 — ALTERATIONS IN THE SKIN

Ch. 51 — Approach to the Patient with Skin Disease (Ch. 56 in Harrison's)

Ch. 52–57 — Specific Skin Disorders (Covered in earlier summaries)

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SECTION 9 — HAEMATOLOGICAL ABNORMALITIES

Ch. 58 — Anaemia and Polycythaemia (Ch. 63 in some editions)

• Anaemia: Hb <13 g/dL (men), <12 g/dL (women)
• Classification:

• Haemolytic anaemia: ↑reticulocytes, ↑LDH, ↑unconjugated bilirubin, ↓haptoglobin; Coombs test (AIHA)
• Polycythaemia vera: JAK2 V617F mutation; ↑RBC, WBC, platelets; splenomegaly; risk of thrombosis and myelofibrosis; Tx: phlebotomy, hydroxyurea

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Ch. 59 — Bleeding and Thrombosis (Ch. 64)

• Primary haemostasis (platelet plug): vWF → GPIb → platelet adhesion; ADP, TXA₂ → platelet aggregation via GPIIb/IIIa
• Secondary haemostasis (coagulation cascade): Intrinsic (PT → XII, XI, IX, VIII) → Extrinsic (aPTT → VII, TF) → Common (X, V, II, I)
• Bleeding disorders:
  • Platelet/vascular: Petechiae, purpura, mucosal bleeding; PT/aPTT normal
  • Coagulation factor: Deep haematomas, haemarthroses; prolonged PT/aPTT
  • DIC: Simultaneous bleeding + clotting; ↓platelets, ↑PT/aPTT, ↑D-dimer, ↓fibrinogen; treat underlying cause
• Thrombophilia: DVT/PE; Factor V Leiden (most common inherited), prothrombin mutation, protein C/S deficiency, ATIII deficiency, antiphospholipid syndrome (APLS)

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Ch. 60 — Enlargement of Lymph Nodes and Spleen (Ch. 65)

• Lymphadenopathy:
  • Localised: Drainage territory infection/malignancy; cervical (EBV, head/neck cancer), inguinal (STI, lymphoma), axillary (breast cancer)
  • Generalised: EBV, CMV, HIV, SLE, sarcoidosis, lymphoma, leukaemia
  • Red flags: Firm/hard/fixed, >2 cm, >4 weeks, B symptoms (fever, night sweats, weight loss), supraclavicular location → biopsy
• Splenomegaly:
  • Massive: CML, myelofibrosis, malaria, Gaucher's, hairy cell leukaemia
  • Moderate: Lymphoma, portal hypertension, haemolytic anaemia
  • Mild: Most infections, SLE, RA (Felty's syndrome)
  • Hypersplenism: Pancytopenia from sequestration

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Ch. 61 — Disorders of Granulocytes and Monocytes (Ch. 66)

• Neutropenia: ANC <1500; severe <500 → high infection risk (gram-negative bacteraemia, fungal)
  • Causes: Drug-induced (chemotherapy, clozapine, carbimazole), viral, aplastic anaemia, SLE, Felty's
  • Febrile neutropenia: Oncological emergency — IV broad-spectrum antibiotics within 1h; piperacillin-tazobactam ± aminoglycoside
• Neutrophilia: ANC >7500; causes: bacterial infection, steroid use, AMI, burns, CML
• Eosinophilia: >500; allergic disease, parasites (especially tissue-invasive), EGPA, Addison's, malignancy (Löffler's syndrome)
• Monocytosis: >800; TB, infective endocarditis, CMML, IBD

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Ch. 62 — Peripheral Blood Smear (Covered in detail above)

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SECTION 10 — MUSCULOSKELETAL

Ch. 63 — Approach to Articular and Musculoskeletal Disease

• Articular vs. periarticular: True joint swelling + restricted active AND passive ROM = articular; periarticular (bursitis, tendinitis) = pain only with resisted active movement
• Inflammatory vs. non-inflammatory:
  • Inflammatory: Morning stiffness >1h, warmth, ↑ESR/CRP, systemic features
  • Non-inflammatory: Brief stiffness, mechanical, normal inflammatory markers
• Mono- vs. oligo- vs. polyarthritis:
  • Monoarthritis: Septic arthritis (emergency), gout, pseudogout, haemarthrosis
  • Oligoarthritis (2–4 joints): Reactive arthritis, psoriatic, IBD-associated
  • Polyarthritis (>4 joints): RA, SLE, viral arthritis, OA
• Synovial fluid analysis: Cell count, crystals (gout = needle-shaped, negatively birefringent; pseudogout = rhomboid, positively birefringent), Gram stain and culture

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Ch. 64 — Osteoporosis

• ↓Bone mineral density (BMD); T-score ≤-2.5 on DEXA = osteoporosis; T-score -1 to -2.5 = osteopaenia
• Risk factors: Female, postmenopausal, ↓calcium/Vit D, smoking, alcohol, steroids, hyperthyroidism, CKD, RA, low BMI
• FRAX score: 10-year fracture probability
• Fragility fractures: Vertebral (most common — often asymptomatic), hip (highest mortality — 20–30% at 1yr), Colles' (distal radius)
• Treatment: Calcium + Vit D → bisphosphonates (alendronate, zoledronate — first-line); denosumab, romosozumab, teriparatide (anabolic — severe/refractory)
• Osteomalacia: Defective mineralisation; ↓Vit D; looser zones; ↑ALP, ↓Ca, ↓PO₄

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Ch. 65 — Approach to the Patient with Neurological Disease

• History: Onset (sudden = vascular, gradual = degenerative/mass), location, progression, prior episodes
• Localisation before aetiology: Cortex → subcortex → brainstem → cerebellum → spinal cord → peripheral nerve → NMJ → muscle
• Key neurological examination: Mental status, cranial nerves, motor (tone, power, coordination), reflexes, sensory, gait
• Neuroimaging: CT (quick — haemorrhage, acute stroke); MRI (superior for parenchyma, posterior fossa, spinal cord)
• LP: Meningitis/encephalitis (after CT), SAH, MS (oligoclonal bands), GBS (albuminocytological dissociation)

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Ch. 66 — Neuroimaging in Neurological Disease

• CT: Fast, widely available; best for acute haemorrhage, bone, calcification; limited posterior fossa
• MRI: Superior soft tissue contrast; T1 (anatomy — fat bright, CSF dark), T2 (pathology — oedema/CSF bright), FLAIR (suppresses CSF — highlights periventricular lesions in MS), DWI (acute ischaemia — bright within minutes), GRE/SWI (microhaemorrhages)
• MRA/MRV: Non-invasive vascular imaging; aneurysm, AVM, venous sinus thrombosis
• CT angiography: Fast; stroke work-up, aortic dissection
• Functional MRI (fMRI): Pre-surgical mapping of eloquent cortex
• PET: Amyloid PET (Alzheimer's), FDG-PET (epilepsy, tumour vs. radiation necrosis)
• Key patterns:
  • MS: Periventricular, juxtacortical, infratentorial T2 lesions; Dawson's fingers
  • Acute ischaemic stroke: DWI bright + ADC dark (cytotoxic oedema)
  • SAH: Hyperdense CSF in basal cisterns on CT; CT sensitivity ~98% in first 6h

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Master Summary Table — Chapters 13–66

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Chapter 4 — Evidence-Based Medicine (EBM)

Harrison's Principles of Internal Medicine, 21st Edition

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Definition

"Clinical medicine is defined traditionally as a practice combining medical knowledge (including scientific evidence), intuition, and judgment in the care of patients. Evidence-based medicine updates this construct by placing much greater emphasis on the processes by which clinicians gain knowledge of the most up-to-date and relevant clinical research to determine for themselves whether medical interventions alter the disease course and improve the length or quality of life." — Harrison's, p. 269

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The 4 Key Steps (Processes) of EBM

Step 1 — Formulate a Focused Clinical Question (PICO)

• Question types: Therapy, Diagnosis, Prognosis, Harm, Aetiology
• Well-built questions are specific, clinically relevant, and searchable

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Step 2 — Search for the Best Available Evidence

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Step 3 — Critically Appraise the Evidence

A. Hierarchy of Evidence (Levels of Evidence)

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B. Study Design — Key Types

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C. Assessing Risk of Bias (Internal Validity)

1. Was randomisation adequate (allocation concealment)?
2. Was blinding implemented (patients, clinicians, outcome assessors)?
3. Were all participants accounted for (intention-to-treat analysis)?
4. Were groups similar at baseline?
5. Was follow-up complete and equal?

• Cochrane RoB 2 (RCTs)
• ROBINS-I (observational studies)
• GRADE framework (overall quality of evidence → High/Moderate/Low/Very Low)

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Step 4 — Apply the Evidence to the Individual Patient

1. Best external evidence (research findings)
2. Clinical expertise (experience, judgment, knowledge of patient context)
3. Patient values and preferences (shared decision-making)

• Is this patient similar to those in the study (external validity/generalisability)?
• Are the outcomes measured the ones that matter to this patient?
• What are the patient's values regarding risk/benefit trade-offs?

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Key Tools and Statistical Concepts in EBM

A. Diagnostic Tests

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B. Measures of Treatment Effect

Critical teaching point: RRR is always more impressive-sounding than ARR. A drug reducing events from 2% to 1% has RRR = 50% but ARR = 1% and NNT = 100. Clinicians must focus on ARR and NNT for bedside decision-making.

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C. Meta-Analysis Tools

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D. GRADE Framework — Evaluating Evidence Quality

• Strong: "We recommend..." (benefits clearly outweigh risks)
• Weak/Conditional: "We suggest..." (benefits and risks finely balanced or uncertain)

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E. Clinical Decision Rules and Scores

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F. Shared Decision-Making (SDM)

1. Clinician provides: Evidence (risks, benefits, alternatives), clinical expertise
2. Patient provides: Values, preferences, life goals, acceptable risk threshold
3. Together decide: Best option for that individual

• Evidence is uncertain or conflicting
• Multiple equivalent options exist
• Treatment involves significant trade-offs (e.g., cancer screening, elective surgery, anticoagulation)

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Limitations of EBM

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Summary: EBM in Practice

Clinical Uncertainty
        ↓
Step 1: PICO Question
        ↓
Step 2: Search (PubMed, Cochrane, Guidelines)
        ↓
Step 3: Appraise (Study design → Bias → Statistics)
              ↓
        Level of evidence (GRADE)
              ↓
        NNT / ARR / LR / CI
        ↓
Step 4: Apply to patient
              ↓
        Clinical expertise + Patient values
              ↓
        Shared Decision-Making
              ↓
        Best individualised care

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Key Teaching Points (Harrison's Ch. 4)

1. EBM does not replace clinical judgment — it enhances it by combining evidence, expertise, and patient values
2. RCTs are not always the answer — for rare diseases, long latency outcomes, or ethical constraints, observational studies may be the best available evidence
3. Always distinguish statistical significance from clinical significance
4. NNT and ARR are more clinically useful than RRR — always calculate when appraising therapy trials
5. Sensitivity/specificity are fixed properties of a test; PPV/NPV change with disease prevalence — critical for interpreting tests in low vs. high prevalence populations
6. LRs are the most useful single statistic for diagnostic test interpretation as they are independent of prevalence when using Bayesian reasoning
7. GRADE is the current gold standard for rating evidence quality and translating it into clinical recommendations
8. The 17-year evidence-to-practice gap underscores the importance of clinicians actively engaging with the primary literature

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Chapter 6 — Screening and Prevention of Disease

Harrison's Principles of Internal Medicine, 21st Edition

"This chapter reviews the basic principles of screening and prevention in the primary care setting." — Harrison's, p. 302

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Definition of Screening

• Distinguished from diagnostic testing (applied to symptomatic individuals)
• Screening is applied to apparently healthy populations
• The fundamental goal: detect disease at a pre-symptomatic stage when treatment is more effective

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Levels of Prevention

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Basic Principles of Screening — Wilson and Jungner Criteria (WHO, 1968)

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Properties of an Ideal Screening Test

A. Validity — Does the test measure what it is meant to measure?

Critical point: In low-prevalence screening populations, even a highly specific test generates many false positives — driving unnecessary investigations, anxiety, and harm. This is the fundamental tension in population screening.

B. Reliability (Reproducibility)

• Consistency of results when the test is repeated under same conditions
• Intra-observer and inter-observer variability must be minimised
• Assessed by kappa statistic (κ >0.8 = excellent agreement)

C. Yield

• Number of previously unrecognised cases detected per number screened
• Influenced by: prevalence, test sensitivity, and screening interval

D. Acceptability

• Non-invasive, affordable, with minimal discomfort
• Respects cultural, ethical, and personal patient values

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The Screening Process — Key Steps

Define target population (age, sex, risk group)
        ↓
Apply screening test (first-line, usually cheap/safe/sensitive)
        ↓
Screen-positive individuals
        ↓
Diagnostic confirmation (gold standard test)
        ↓
Treatment / intervention
        ↓
Outcome monitoring and programme evaluation

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Uses of Screening Tests

1. Population-Based (Mass) Screening

• Cervical cancer screening (Pap smear / HPV test)
• Breast cancer (mammography)
• Colorectal cancer (faecal occult blood test / colonoscopy)
• Newborn metabolic screening (PKU, hypothyroidism, CF)
• Neonatal hearing screening

2. Selective (Targeted / High-Risk) Screening

• BRCA1/2 testing in women with strong family history of breast/ovarian cancer
• Lung cancer screening (low-dose CT) in heavy smokers aged 50–80
• Hepatocellular carcinoma screening (USS liver ± AFP) in cirrhosis/hepatitis B
• Abdominal aortic aneurysm (USS) in male smokers aged 65+
• TB screening in healthcare workers, immigrants from endemic areas

3. Opportunistic Screening

• Blood pressure measurement at any GP visit
• Fasting glucose/HbA1c in overweight patients
• Cholesterol in cardiovascular risk assessment

4. Multiphasic Screening

• Health checks (NHS Health Check in UK — BP, cholesterol, glucose, BMI)
• Executive health screenings

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Abuses and Limitations of Screening — Critical Biases

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1. Lead Time Bias

Without screening:   Diagnosis ──────────────────► Death
                                  ← Survival time →

With screening:      Diagnosis ──────────────────────────► Death
                        ↑ (earlier)
                     ← Longer "survival" → (same death date)

• The patient appears to "survive longer" after diagnosis, but dies at the same time
• Survival time is measured from diagnosis → death; earlier diagnosis inflates this without any true benefit
• Corrective measure: Use disease-specific mortality rates (deaths per 100,000 per year) as the outcome, NOT 5-year survival rates

Example: If screening detects cancer 2 years earlier but treatment does not change the death date, 5-year survival improves from 0% to 100% purely due to lead time — with no actual benefit.

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2. Length-Biased Sampling (Length Time Bias)

Slow-growing tumour:   ─────────────────────────────► (long window, screen catches it)
Fast-growing tumour:       ──────► (short window, screen misses it → symptomatic)

• Screened populations therefore contain a disproportionately large number of indolent cancers with inherently good prognosis — inflating apparent screening benefit
• The patients who most need early detection (aggressive cancers) are least likely to be caught

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3. Overdiagnosis and Overtreatment

• An extreme form of length-biased sampling
• The reservoir of slow-growing, clinically insignificant tumours is large
• Problem compounded by competing causes of death in elderly patients
• Consequences: Unnecessary surgery, radiation, chemotherapy, psychological harm, financial cost

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4. Selection Bias (Healthy Screener Effect / Volunteer Bias)

• Screened populations have lower all-cause mortality than unscreened populations even for unrelated diseases
• Makes screening appear more effective than it truly is
• Corrective measure: Randomised controlled trials of screening (randomise to screened vs. unscreened), not observational comparisons

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5. Will Rogers Phenomenon (Stage Migration Bias)

Named after the quote: "When the Okies left Oklahoma and moved to California, they raised the average intelligence in both states."

• Example: CT staging detects micrometastases previously missed → patients previously stage II become stage III → stage II survival improves (sicker patients removed) AND stage III survival improves (less sick patients added)
• Net effect: Survival in every stage improves with no actual benefit to patients

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6. False Positives — Harms of Screening

• Anxiety and psychological distress (even after negative confirmatory test)
• Unnecessary investigations: Invasive, expensive, risky (e.g., lung nodule follow-up CT scans, colposcopy, breast biopsy)
• Cascading investigations: One false positive leading to multiple downstream tests
• Overtreatment: Treatment of conditions that would never have caused harm

Example: Low-dose CT lung screening — for every 1,000 scans, ~200 abnormalities detected; vast majority are benign, leading to repeated imaging and occasional invasive procedures.

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7. False Negatives — Harms of Screening

• False reassurance → patient ignores subsequent symptoms
• Missed cancers between screening intervals = interval cancers (often more aggressive)
• Reduces the positive predictive value of subsequent symptoms

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8. Medicalisation and Psychological Harm

• Labelling effect: Being told one has a "borderline" or "pre-disease" state (pre-diabetes, pre-hypertension, DCIS) causes anxiety, reduces quality of life, and may lead to unnecessary treatment
• Surveillance burden: Serial investigations, appointments, and follow-up cause long-term psychological stress
• Healthy individuals converted into patients

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Evaluating a Screening Programme — What Outcomes Matter?

The most important principle: A screening test must be evaluated by randomised controlled trial measuring disease-specific or all-cause mortality — not by case series or cohort studies showing improved survival.

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Balancing Benefits and Harms — The Core Ethical Tension

1. What the test is designed to detect
2. The possibility of false-positive and false-negative results
3. What further investigations a positive result would entail
4. The risk of overdiagnosis and overtreatment
5. The potential benefits in terms of reduced mortality

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Examples of Current Evidence-Based Screening Programmes

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Summary Table — Uses vs. Abuses

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Key Teaching Points (Harrison's Ch. 6)

1. Screening must satisfy Wilson-Jungner criteria — most importantly, treatment must be available and early detection must confer genuine benefit
2. 5-year survival is a useless metric for evaluating screening — always use disease-specific mortality rates from RCTs
3. Lead time bias and length bias are the two most important reasons why screening trials must be randomised
4. Overdiagnosis is the most underappreciated harm of modern screening — most prominent in prostate, thyroid, breast, and lung cancer screening
5. In low-prevalence populations, even highly specific tests generate predominantly false positives — PPV collapses as prevalence falls
6. PSA screening remains the textbook example of a controversial screening test: reduces metastatic prostate cancer but with substantial overdiagnosis and overtreatment
7. Screening is not risk-free — it is an intervention offered to healthy people, requiring a higher ethical standard and genuine informed consent
8. The most valuable screening programmes combine high sensitivity (to not miss disease) at the first-line test with high specificity at the confirmatory diagnostic test

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Part I — Bayes' Rule in Diagnostic Probability

Harrison's Principles of Internal Medicine, 21st Edition — Chapter 4

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The Core Concept

The Fagan nomogram version of Bayes' rule "helps us understand at a conceptual level how it estimates the posttest probability of disease... the impact of the diagnostic test result is summarized by the likelihood ratio, defined as the ratio of the probability of a given test result in a patient with disease to the probability of that result in a patient without disease." — Harrison's, p. 261

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Foundational Definitions

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Bayes' Theorem — The Formula

Classic Form

• P(D) = pre-test probability (prevalence)
• P(T+|D) = sensitivity
• P(T+|D̄) = 1 − specificity (false positive rate)
• P(D|T+) = post-test probability (PPV in population terms)

Simplified Practical Form Using Odds

The Bedside Bayes Formula (Using LR)

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Likelihood Ratios — The Key Tool

Definition

Interpretation of LR Values

Key insight: LRs are independent of prevalence — unlike PPV and NPV, they are properties of the test alone and can be applied to any pre-test probability using Bayesian reasoning.

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Worked Clinical Example

• Sensitivity = 68%, Specificity = 77%
• LR+ = 0.68 / (1 − 0.77) = 2.96

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The Fagan Nomogram

Pre-test         Likelihood          Post-test
Probability      Ratio               Probability

99% ──────────── 1000 ─────────────── 99%
                  500
95% ──────────── 200 ──────────────── 95%
                  100
90% ──────────── 50  ──────────────── 90%
                  20
75% ──────────── 10  ──────────────── 75%
50% ──────────── 5   ──────────────── 50%
                  2
25% ──────────── 1   ──────────────── 25%
10% ──────────── 0.5 ──────────────── 10%
5%  ──────────── 0.2 ──────────────── 5%
                  0.1
1%  ──────────── 0.05 ─────────────── 1%

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The Threshold Model of Clinical Decision-Making

0%─────────────[Test threshold]────────[Treatment threshold]──────100%
         │                    │                    │
    Disease          Test to             Treat without
  so unlikely     further clarify         testing
  no test needed   probability

Testing is only worthwhile when the pre-test probability lies between the test and treatment thresholds — and when the test result will change clinical management.

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Pre-Test Probability — How to Estimate It

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Key Limitations of Bayesian Reasoning in Practice

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Part II — Tools for Assessment of Quality of Healthcare

Harrison's Principles of Internal Medicine, 21st Edition

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Donabedian's Triad — The Foundational Framework

"Donabedian has suggested that quality of care can be categorised by type of measurement into structure, process, and outcome."

1. Structure

• Physical resources: Hospital beds, equipment, catheterisation laboratory, ICU
• Human resources: Staffing ratios, nurse-to-patient ratio, specialist availability
• Organisational features: Electronic health records (EHR), protocols, accreditation status
• Example: Does the hospital have a primary PCI-capable catheterisation laboratory?

2. Process

• Whether aspirin was given to a patient with suspected MI (Harrison's, p. 356)
• Whether a Pap smear was performed at the recommended interval (Harrison's, p. 356)
• Whether hand hygiene was performed before invasive procedures
• Whether a DVT prophylaxis protocol was followed
• Example: Door-to-balloon time <90 minutes in STEMI

3. Outcome

• Mortality rates (30-day, 1-year)
• Complication rates (surgical site infection, readmission, hospital-acquired infection)
• Patient-reported outcomes (pain, function, quality of life)
• Example: 30-day mortality after MI, hospital-acquired pressure ulcer rate

"It is important to note that good structure and process do not always result in a good outcome. A patient may present with suspected MI to an institution with a catheterisation laboratory and receive recommended care including aspirin, but still die because of the infarction." — Harrison's, p. 356

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Tools for Quality Measurement and Improvement

1. Clinical Audit

• Systematic review of clinical care against explicit standards
• Audit cycle: Set standard → Measure practice → Compare to standard → Implement change → Re-audit (close the loop)
• Example: Audit of antibiotic prescription within 1 hour for sepsis against NICE guidelines
• Limitation: Descriptive — identifies gaps but does not establish causation

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2. Key Performance Indicators (KPIs) and Quality Indicators

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3. Balanced Scorecard

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4. Plan-Do-Study-Act (PDSA) Cycle

      PLAN
   ↗        ↘
ACT          DO
   ↖        ↙
      STUDY

• Plan: Identify problem, set objective, predict outcome
• Do: Implement change on small scale (pilot)
• Study: Analyse results; compare to prediction
• Act: Standardise if successful; modify and repeat if not

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5. Root Cause Analysis (RCA)

• Structured retrospective review of adverse events or near-misses
• Goal: Identify systemic (not individual) causes of failure
• Tools within RCA:
  • Fishbone diagram (Ishikawa): Categorises causes into Man, Machine, Method, Material, Measurement, Environment (6Ms)
  • 5 Whys: Ask "why?" repeatedly until root cause reached
  • Fault Tree Analysis: Logical diagramming of failure pathways
• Outcome: Systemic recommendations, not blame allocation

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6. Failure Mode and Effects Analysis (FMEA)

• Prospective (proactive) risk assessment tool — used before an adverse event
• Identify potential failure modes in a process → assess their likelihood, severity, and detectability
• Calculate Risk Priority Number (RPN) = Severity × Occurrence × Detectability
• Prioritise interventions for highest RPN failures
• Widely used in pharmacy, surgery, and radiology workflows

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7. Statistical Process Control (SPC) Charts

• Monitor quality indicators over time using statistical rules
• Distinguish common cause variation (inherent process variability — expected) from special cause variation (unexpected signals requiring investigation)
• Control limits = ±3 standard deviations from mean
• Types: P-charts (proportions), U-charts (rates), XmR charts (individual measurements)
• Advantage over simple audit: Detects trends and shifts in performance before they become crises

         UCL ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
              ●   ●       ●
Mean ────────────────●────────●────●────────────
                         ●              ●  ●
         LCL ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─

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8. Benchmarking

• Comparing an institution's performance against:
  • Internal benchmark: Own historical performance
  • External benchmark: Peer institutions or national standards
  • Best practice benchmark: Against the highest performers
• Requires risk adjustment for fair comparison (case-mix, comorbidities, deprivation indices)
• Tools: NHS Model Hospital, CMS Hospital Compare, Dr Foster Intelligence, OECD Health Statistics

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9. Patient-Reported Outcome Measures (PROMs) and Experience Measures (PREMs)

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10. Accreditation and External Review

• Joint Commission (USA) / CQC (UK) / JCI (International): External bodies that assess healthcare organisations against defined standards
• Surveys, inspections, and continuous monitoring
• Focuses on structure + process standards
• Magnet Status (nursing excellence), ISO 9001 (quality management systems)

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11. Mortality and Morbidity (M&M) Conferences

• Regular multidisciplinary review of adverse outcomes and near-misses
• Non-punitive, educational environment
• Identifies system failures, near-misses, and learning opportunities
• Basis for departmental quality improvement initiatives

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12. Incident Reporting Systems

• Voluntary reporting of adverse events, near-misses, and unsafe conditions
• Examples: NHS National Reporting and Learning System (NRLS), FDA MedWatch, WHO Global Patient Safety Network
• Chronic underreporting (estimated 10–30% of incidents reported)
• Heinrich's Triangle: For every serious injury, there are ~29 minor injuries and 300 near-misses

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13. Patient Safety Indicators (PSIs)

• Hospital-acquired infections (HAI): MRSA, CDiff, CAUTI, CLABSI, VAP
• Surgical complications: Wrong-site surgery, retained foreign body, anastomotic leak
• Medication errors: Wrong drug, wrong dose, wrong patient
• Falls with injury
• Pressure ulcers (hospital-acquired)
• Venous thromboembolism in surgical patients

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14. Six Sigma

• Data-driven methodology for eliminating defects: Target = 3.4 defects per million opportunities
• DMAIC framework: Define → Measure → Analyse → Improve → Control
• Originally industrial (Motorola/GE); increasingly applied in healthcare (reducing medication errors, surgical complications)

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15. Lean Methodology

• Derived from Toyota Production System
• Core principle: Eliminate waste (Muda) in processes — 8 types of waste:
  • DOWNTIME: Defects, Overproduction, Waiting, Non-utilised talent, Transportation, Inventory, Motion, Extra-processing
• Tools: Value stream mapping, 5S (Sort, Set, Shine, Standardise, Sustain), Kaizen (continuous improvement)
• Applied in: ED flow, surgical throughput, pharmacy dispensing, outpatient scheduling

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Summary Table — Quality Tools at a Glance

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Synthesis — Connecting Bayes and Quality

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Polycystic Ovary Syndrome (PCOS)

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Definition

• Hyperandrogenism (HA) — clinical or biochemical
• Ovulatory dysfunction — oligo/anovulation
• Polycystic ovarian morphology on ultrasound

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Pathophysiology

1. GnRH Pulse Abnormality

• Abnormalities in GnRH pulsatility → elevated LH pulse frequency and amplitude
• ↑ LH → stimulates ovarian theca cells → excess androgen (testosterone, androstenedione) production
• Relatively low or normal FSH → impaired follicular maturation and anovulation

2. Ovarian Androgen Excess

• Theca cells in PCOS over-respond to LH stimulation
• Elevated androgens → peripheral conversion to oestrone → unopposed oestrogen → positive feedback on LH → further LH excess (vicious cycle)
• 11-oxygenated androgens (e.g., 11-ketotestosterone) may also be elevated — an alternate androgen source

3. Insulin Resistance and Hyperinsulinaemia

• Insulin resistance — predominantly in skeletal muscle and adipose tissue — is present in 50–80% of women with PCOS
• Compensatory hyperinsulinaemia → directly stimulates ovarian androgen production (insulin receptors on theca cells are preserved even when peripheral resistance exists)
• Insulin also ↓ hepatic SHBG production → more free (unbound) testosterone circulates
• Obesity worsens insulin resistance and the PCOS phenotype significantly

4. Follicular Arrest

• Excess androgens and insulin → accumulation of small antral follicles arrested at 2–9 mm
• None reaches dominance → anovulation persists
• Gives the characteristic "string of pearls" appearance on USS

5. Genetic Basis

• Genome-wide association studies (GWAS) have identified ~19 loci associated with PCOS across diverse populations (Harrison's 22E)
• Cluster analyses reveal reproductive and metabolic subtypes
• Likely polygenic and multifactorial inheritance
• Familial concordance: sisters and mothers of PCOS patients have higher rates of PCOS

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Diagnostic Criteria

Rotterdam Criteria (2003) — Most Widely Used

Diagnostic Phenotypes (4 Rotterdam Phenotypes)

Phenotype A is most severe metabolically; Phenotype D is mildest.

NIH 1990 Criteria (Stricter — Both Required)

1. Chronic anovulation
2. Clinical and/or biochemical hyperandrogenism + exclusion of other causes

Special Populations

• Adolescents: Diagnosis requires both irregular menses AND hyperandrogenism; ultrasound and AMH criteria are not used (multi-follicular ovaries and elevated AMH are normal in adolescence); wait at least 3 years post-menarche before confirming (Harrison's 22E)
• Lean PCOS: High LH with normal-low FSH and oestradiol; insulin resistance still present in ~30%

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Exclusion Criteria — Diagnoses to Rule Out

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Clinical Features

Menstrual Disturbance

• Oligomenorrhoea (most common) — cycles >35 days
• Amenorrhoea — primary or secondary
• Irregular uterine bleeding
• Rarely, normal cycles with biochemical hyperandrogenism

Hyperandrogenism

• Hirsutism: Coarse terminal hair in androgen-sensitive areas (upper lip, chin, chest, abdomen, inner thighs) — assessed by modified Ferriman-Gallwey (mFG) score (≥4–6 abnormal, ethnicity-dependent)
• Acne: Persistent, adult-onset
• Androgenic alopecia: Temporal recession, central thinning
• Virilisation (clitoromegaly, voice deepening) is RARE and suggests tumour

Metabolic Features

• Obesity: Present in 40–80% of PCOS patients in Western populations; central (android) distribution
• Insulin resistance: Present in ~50–80%; leads to acanthosis nigricans (velvety hyperpigmentation at neck, axillae)
• Metabolic syndrome: ↑ waist circumference, ↑ triglycerides, ↓ HDL, hypertension, impaired fasting glucose
• Type 2 diabetes: 5–10× higher risk; impaired glucose tolerance in 30–35%
• Dyslipidaemia: ↑ LDL, ↑ TG, ↓ HDL

Reproductive Features

• Infertility: Most common cause of anovulatory infertility
• Subfertility: Infrequent ovulation
• Pregnancy complications: ↑ risk of miscarriage, gestational diabetes, gestational hypertension, pre-eclampsia, preterm birth (Harrison's 22E)

Long-Term Health Risks

• Endometrial cancer: 2–6× increased risk from unopposed oestrogen due to chronic anovulation (Harrison's 22E)
• Cardiovascular disease: ↑ risk from metabolic syndrome, dyslipidaemia, hypertension; however, direct evidence of increased CV mortality remains debated
• Obstructive sleep apnoea (OSA): Independent of BMI (Harrison's 22E)
• Metabolic dysfunction-associated steatotic liver disease (MASLD/MAFLD): Independent of BMI (Harrison's 22E)
• Depression and anxiety: High prevalence; body image distress and disordered eating (Harrison's 22E)

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Investigations

Baseline (All patients)

Imaging

• Pelvic ultrasound (transvaginal preferred):
  • ≥20 antral follicles per ovary (2023 updated threshold)
  • OR ovarian volume ≥10 cm³
  • "String of pearls" sign: multiple peripheral small follicles 2–9 mm
  • Note: USS criteria not applied in adolescents or women on OCP

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Management

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1. Lifestyle Modification (All patients)

• First-line for all women with PCOS (Harrison's 22E)
• 5–10% weight loss in overweight/obese women:
  • Restores ovulation in up to 80%
  • ↓ androgens, ↓ insulin resistance, ↓ LH, ↑ SHBG
  • Improves metabolic parameters
• Low glycaemic index diet, aerobic + resistance exercise
• Pre-pregnancy counselling and lifestyle optimisation recommended before attempting conception (Harrison's 22E)

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2. Menstrual Regulation and Endometrial Protection

Combined Hormonal Contraceptives (CHC) — First-line (not seeking pregnancy)

• Regulate cycles; ↑ SHBG → ↓ free testosterone → treat hirsutism/acne
• Androgen effects improve by 2–3 months; hirsutism improvement takes longer (6–12 months)
• Use lowest effective oestrogen dose, cyclic or continuous
• Progestins alone if CHC contraindicated:
  • Medroxyprogesterone acetate 10 mg daily × 10–14 days every 1–3 months
  • Micronised progesterone 200 mg daily × 10–14 days every 3 months
  • Levonorgestrel IUD (Mirena)

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3. Hyperandrogenism (Hirsutism/Acne)

Metformin is NOT recommended for treating hyperandrogenic symptoms alone (Harrison's 22E)

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4. Metabolic Risk Management

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5. Fertility / Ovulation Induction

Ovarian hyperstimulation syndrome (OHSS): Major risk in PCOS — prevent with low-dose gonadotropin protocols, GnRH agonist trigger, and freeze-all strategies

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6. Screening and Monitoring

• Obesity (BMI, waist circumference)
• Hypertension
• Glycaemic control (fasting glucose/HbA1c ± OGTT)
• Lipid profile (overweight/obese women)
• Depression and anxiety
• Endometrial protection (ensure regular withdrawal bleeds)

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Summary — PCOS at a Glance

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What Is Insulin Resistance?

"A decreased biological response to normal concentrations of circulating insulin." — Tietz Textbook of Laboratory Medicine, 7th Ed.

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Gold Standard — Euglycaemic-Hyperinsulinaemic Clamp

• A constant IV insulin infusion is given in one arm
• A variable IV glucose infusion in the other arm maintains blood glucose at normal fasting levels
• The glucose infusion rate (GIR) required to maintain euglycaemia = measure of insulin sensitivity
• Higher GIR = more sensitive; Lower GIR = more resistant
• Performed in hospital under close medical supervision — not remotely approximable at home
• Complex, expensive, and impractical for routine or population use

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Clinical Surrogate Measures (Requiring a Lab)

1. HOMA-IR (Homeostatic Model Assessment of Insulin Resistance)

"A simpler but indirect approach — a calculation derived from fasting glucose and insulin concentrations." — Tietz Textbook of Laboratory Medicine, 7th Ed.

• Poor precision
• Insulin assays vary significantly between laboratories (no universal standardisation)
• Does not account for hepatic vs. peripheral IR separately
• Affected by beta-cell dysfunction (low insulin + high glucose can give misleading low HOMA-IR)

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2. Fasting Insulin Alone

• Normal fasting insulin: 2–25 μIU/mL (varies by assay; Tietz)
• More specific assays: <10 μIU/mL as upper normal
• Elevated fasting insulin in the presence of normal glucose = hyperinsulinaemia compensating for IR
• Requires a lab — not measurable at home

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3. OGTT-Derived Indices

"OGTT-derived insulin sensitivity indices may be preferred to fasting sample-derived indices." — Brenner & Rector's The Kidney

• Matsuda Index (ISI-composite): Calculated from glucose and insulin values during a 75 g OGTT at 0, 30, 60, 90, 120 minutes
• More accurate than HOMA-IR as it reflects both fasting and post-load insulin dynamics
• Requires laboratory measurement at multiple time points — clinic-based only

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4. TyG Index (Triglyceride-Glucose Index)

• Validated surrogate for IR — correlates well with clamp studies
• Requires fasting lipid panel + fasting glucose from a lab
• Cutoff: TyG ≥8.5 suggests insulin resistance
• Advantage: Uses routine labs already ordered; no insulin assay needed

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5. Metabolic Syndrome Criteria as a Clinical Proxy

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What Can Actually Be Done At Home?

A home glucose meter gives capillary blood glucose only — it does not measure insulin and cannot calculate HOMA-IR.

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"Home IR Test Kits" — Commercial Products

• A finger-prick blood sample sent by post to a laboratory
• Results returned online
• Often measure: fasting glucose, HbA1c, fasting insulin, and calculate HOMA-IR

• These are mail-order laboratory tests, not truly "home tests" — the measurement still happens in a certified laboratory
• Validity depends entirely on: whether the user was truly fasting, blood sample handling quality, and lab insulin assay standardisation
• HOMA-IR calculated from a mail-order kit is a reasonable surrogate if properly performed, but results should be interpreted by a clinician in clinical context
• Not endorsed by any major clinical guideline as a standalone diagnostic tool

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Summary

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Interpretation

Example Calculation

• Fasting insulin = 12 μIU/mL
• Fasting glucose = 5.5 mmol/L
• HOMA-IR = (12 × 5.5) / 22.5 = 2.93 → moderate insulin resistance

Requirements

• Both values must be drawn after 8–12 hours of overnight fasting
• Venous blood sample only — home glucometer readings are not accurate enough for this calculation

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Example

• Fasting insulin = 12 μIU/mL
• Fasting glucose = 99 mg/dL

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Quick Reference — Common Glucose Values

Crigler-Najjar Syndrome: Type I vs Type II

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Side-by-Side Comparison

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Pathophysiology Summary

UGT1A1 mutation
        ↓
Type I: Zero enzyme → bilirubin accumulates → crosses BBB → kernicterus
Type II: <10% enzyme → bilirubin elevated but lower → kernicterus only under stress

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Why Phenobarbital Works in Type II but Not Type I

• Phenobarbital is an inducer of the constitutive androstane receptor (CAR) → upregulates UGT1A1 gene expression
• In Type II: residual enzyme exists → phenobarbital amplifies it → bilirubin falls to safe levels (2–5 mg/dL)
• In Type I: no functional enzyme present at all → nothing to induce → no response

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Spectrum of UGT1A1 Disorders

Gilbert syndrome = same enzyme, same pathway, but only a promoter mutation (UGT1A1*28) causing reduced transcription — clinically benign.

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Key Mnemonics

• Type I = Incompatible with life without treatment; Inducer (phenobarbital) doesn't work; needs Immediate liver transplant
• Type II = Treatable with Tablet (phenobarbital); Tolerable bilirubin levels