1) Core orientation for screening (both types)

1. Scan at low power first
   • Epidermal thickness/pattern (regular, psoriasiform, atrophic, acanthotic)
   • Stratum corneum type (orthokeratosis/parakeratosis; compact/loose)
   • Dermoepidermal junction contour (rete ridges present/absent, elongation)
   • Distribution of inflammation (superficial, deep, periappendageal, perivascular, lichenoid, interface, diffuse)
   • Presence/absence of adnexa (hair follicles, sebaceous glands, eccrine units)
2. Then high power
   • Keratinocyte maturation, spongiosis, dyskeratosis, cytologic atypia
   • Basal layer change and pigment transfer
   • Inflammatory cell type
   • Vessel/endothelial changes
   • Neural/mechanoreceptor structures (if present)

2) Thick skin histology (palms/soles)

A. Epidermis

• Very thick epidermis, especially:
  • Stratum corneum: markedly thick, compact orthokeratosis
  • Stratum lucidum: distinct eosinophilic translucent band (key feature)
  • Stratum granulosum: prominent
  • Stratum spinosum: well-developed
• Rete ridges: deep and often regular; pronounced interdigitation with dermal papillae
• No hair follicles, no sebaceous glands, no apocrine glands

B. Dermis and adnexa

• Dense papillary and reticular dermis
• Abundant eccrine sweat glands/ducts (acrosyringia visible traversing epidermis)
• Mechanoreceptors may be conspicuous:
  • Meissner corpuscles in dermal papillae
  • Pacinian corpuscles deeper dermis/subcutis (especially volar skin)

C. Histopath screening cues in thick skin biopsies

• Hyperkeratotic lesions can appear “exaggerated” due to baseline thick SC
• Don’t overcall pathologic acanthosis without comparing to expected thick-skin baseline
• Focus on:
  • Cornoid/keratin abnormalities pattern
  • Acral-specific interface changes
  • Eccrine-centered pathology (e.g., neutrophils in acrosyringium for palmoplantar pustular processes)

3) Thin skin histology (most body surface)

A. Epidermis

• Thinner epidermis
• Stratum corneum: relatively thin
• Stratum lucidum: absent
• Stratum granulosum: thinner/less prominent than thick skin
• Rete ridges usually less deep and more variable by site

B. Dermis and adnexa

• Hair follicles present
• Sebaceous glands present (except certain regions)
• Eccrine glands present but less dominant than in thick skin
• Apocrine units in site-specific areas (axilla, anogenital, areola)

C. Histopath screening cues in thin skin biopsies

• Follicular and sebaceous pathology becomes central:
  • Folliculitis patterns
  • Perifollicular fibrosis/inflammation
  • Sebaceous alteration
• Interface and adnexotropic infiltrates easier to localize to follicular units
• Atrophy is easier to appreciate due to thinner baseline epidermis

4) Side-by-side “must know” comparison table

5) Practical histopathology screening algorithm (dermatopath)

1. Identify site phenotype first: thick vs thin skin
2. Confirm expected adnexa:
   • If acral sample shows follicles/sebaceous glands, question specimen labeling or site mix
3. Assess epidermal reaction pattern:
   • Spongiotic, psoriasiform, lichenoid/interface, vesiculobullous, granulomatous surrogate signs
4. Assess cornification pattern:
   • Orthokeratosis/parakeratosis, compactness, focal columns, neutrophils in cornified layer
5. Assess appendageal involvement (thin skin especially):
   • Perifollicular, intrafollicular, peri-eccrine
6. Assess dermal inflammation pattern and depth
7. Correlate with site-adjusted normal baseline before calling abnormal

6) Common pitfalls in thick vs thin skin interpretation

• Acral skin:
  • Baseline thick SC and acanthosis can mimic chronic dermatitis/psoriasiform change
  • Eccrine duct prominence can be misread as adnexal proliferation
• Thin skin:
  • Tangential sectioning can falsely suggest epidermal thinning or rete flattening
  • Follicular dropout in scarred areas can be mistaken for naturally non-follicular skin
• Both:
  • Poor orientation and crush artifact create false interface/spongiotic impressions

7) Reporting template (screening level)

• Specimen type/site: compatible with thick vs thin skin features
• Epidermis: thickness, keratinization pattern, granular/lucidum status, rete pattern
• Adnexa: follicles/sebaceous/eccrine/apocrine presence and involvement
• Dermis: inflammatory pattern, depth, vessel changes, fibrosis, edema
• Provisional pattern diagnosis: e.g., spongiotic dermatitis pattern, lichenoid/interface pattern
• Site-adjusted comment: note acral baseline if thick skin

Approach to a Child with Fever and Rash

Introduction

I. History — Key Points (2 marks)

A. Fever characteristics

• Onset, duration, height, pattern (continuous/remittent/step-ladder)
• Relation to rash: fever before rash, simultaneous, or after rash resolution

B. Rash characterization

• Sequence of appearance: centrifugal vs centripetal spread; craniocaudal progression
• Progression: macular → papular → vesicular → pustular → purpuric
• Pruritic vs non-pruritic

C. Epidemiological history

• Contact with similarly ill individuals
• Travel, animal exposure, insect bites
• Vaccination status (especially MMR, varicella, meningococcal)

D. Drug history

• Recent antimicrobials, antiepileptics, NSAIDs (DRESS, SJS risk)

E. Mucosal symptoms

• Oral sores, eye redness, genital involvement → SJS/TEN, Kawasaki disease
• Cough, coryza, conjunctivitis → measles prodrome (3 C's)

II. Clinical Examination — Systematic Assessment (2 marks)

A. General examination

• Toxic vs non-toxic appearance, hemodynamic stability
• Lymphadenopathy (Kawasaki, rubella, EBV, serum sickness)

B. Rash morphology (primary lesion)

C. Distribution

• Face first, then cephalocaudal: measles, rubella
• Trunk first: roseola infantum, drug rash
• Palms and soles involved: RMSF, hand-foot-mouth, secondary syphilis, Kawasaki (erythema/desquamation)
• Centripetal (trunk > periphery): chickenpox
• Centrifugal: RMSF

D. Mucosal examination

• Koplik spots (blue-white on buccal mucosa): pathognomonic — measles
• Strawberry tongue: Kawasaki disease, scarlet fever
• Crusted/bleeding lips, oral erosions: SJS/TEN
• Forchheimer spots (soft palate petechiae): rubella

E. Other systems

• Cardiac: coronary aneurysm in Kawasaki (ECHO mandatory)
• Joints: HSP, serum sickness, reactive arthritis
• Eyes: conjunctivitis in measles, Kawasaki, SJS

III. Classification of Causes — The Classic Six Exanthems

IV. Systematic Differential Diagnosis

A. Viral exanthems

• Measles: 3 C prodrome (cough, coryza, conjunctivitis) + Koplik spots + morbilliform rash with craniocaudal spread
• Rubella: mild fever, retroauricular/suboccipital lymphadenopathy, fine maculopapular rash spreading caudally; Forchheimer spots on palate
• Roseola: high fever for 3–5 days, fever defervesces and rose-pink macular rash appears on trunk — "rash when fever goes"
• Erythema infectiosum: "slapped cheek" facial erythema + lacy reticular rash on extremities; parvovirus B19
• Chickenpox (VZV): pleomorphic lesions in different stages ("dew drops on rose petal"), centripetal, severely pruritic
• Hand-foot-mouth disease (Coxsackievirus A16/EV71): fever, painful oral vesicles/ulcers, vesicles on palms/soles/buttocks

B. Bacterial

• Scarlet fever (GAS): fever, pharyngitis, sandpaper scarlatiniform rash sparing perioral area (circumoral pallor), Pastia lines in flexures, strawberry tongue; rash followed by desquamation
• Staphylococcal scalded skin syndrome (SSSS): Nikolsky sign positive, perioral/perinasal crusting, superficial bullae/desquamation; exfoliative toxin A/B
• Meningococcemia (N. meningitidis): petechial/purpuric non-blanching rash, toxic, septic — dermatological emergency
• Rocky Mountain Spotted Fever (RMSF): tick bite history, high fever, rash starts on wrists/ankles → trunk; petechiae

C. Immune/hypersensitivity

• Kawasaki disease: fever >5 days + ≥4 of 5 criteria (bilateral non-purulent conjunctivitis, mucosal changes/strawberry tongue, polymorphous rash, peripheral edema/erythema, cervical lymphadenopathy); coronary aneurysm risk
• Henoch-Schönlein Purpura (HSP/IgA vasculitis): palpable purpura on buttocks/lower limbs + arthritis + hematuria + abdominal pain
• Drug reaction (DRESS, SJS/TEN):
  • SJS: mucosal erosions ≥2 sites, target lesions, BSA <10% detachment
  • TEN: BSA >30% full-thickness epidermal detachment — ICU emergency
  • DRESS: drug exposure + fever + morbilliform rash + systemic organ involvement + eosinophilia, atypical lymphocytes

D. Rickettsial

• Scrub typhus: eschar at bite site, maculopapular rash, hepatosplenomegaly; Orientia tsutsugamushi

V. Investigations

VI. A Practical Algorithmic Approach

Child with Fever + Rash
        │
        ├── Purpuric/petechial (non-blanching)?
        │         └── YES → Rule out Meningococcemia/DIC FIRST (emergency)
        │                    → Also consider RMSF, HSP
        │
        ├── Vesicular rash?
        │         └── Chickenpox, HFMD, HSV, SSSS
        │
        ├── Morbilliform/maculopapular?
        │         ├── Koplik spots → Measles
        │         ├── Forchheimer spots + LAP → Rubella
        │         ├── Fever gone, rash appears → Roseola
        │         ├── Slapped cheek → Parvovirus B19
        │         └── Drug exposure → Drug rash/DRESS
        │
        ├── Desquamating/Scarlatiniform?
        │         ├── Pharyngitis + circumoral pallor → Scarlet fever
        │         ├── Fever >5 days + conjunctivitis + mucosal → Kawasaki
        │         └── Nikolsky positive → SSSS or TEN
        │
        └── Mucosal erosions?
                  └── SJS/TEN (drug history, BSA assessment)

VII. Management Principles

• Viral exanthems: Supportive — antipyretics, hydration; specific antivirals if indicated (acyclovir in varicella immunocompromised)
• Scarlet fever: Penicillin V or amoxicillin × 10 days
• SSSS: Antistaphylococcal antibiotics (cloxacillin/flucloxacillin), wound care
• Kawasaki disease: High-dose IVIG (2 g/kg single dose) + aspirin + ECHO monitoring
• Meningococcemia: IV ceftriaxone immediately; ICU care
• SJS/TEN: Stop offending drug, supportive care, burns unit if TEN
• DRESS: Stop drug, systemic steroids
• HSP: Most self-limiting; steroids for severe GI/renal involvement

VIII. Red Flag Signs — Must Not Miss

• Non-blanching petechiae/purpura → meningococcemia
• Nikolsky sign positive → TEN/SSSS
• Mucosal involvement ≥2 sites → SJS
• Fever >5 days child + conjunctivitis + mucosal → Kawasaki (coronary risk)
• Toxic appearance + hypotension + rash → Toxic Shock Syndrome / Sepsis
• Eschar at bite site + fever + rash → Rickettsial infection

Conclusion

Cutaneous Lupus Erythematosus (CLE)

Introduction

I. Classification (Gilliam Classification)

A. LE-Specific Skin Disease

B. LE-Non-Specific Skin Disease

• Cutaneous changes seen in SLE but not exclusive to LE (vasculitis, livedo reticularis, Raynaud's, diffuse alopecia, urticaria)

II. Epidemiology

• Predominantly affects women (F:M = 2:1 to 9:1 depending on subtype)
• SCLE: most common in White women aged 15–40
• DLE: young adults; childhood DLE has higher SLE association
• ACLE: closely linked to active SLE
• CLE represents ~10–15% of all LE cases for SCLE; DLE most prevalent chronic subtype

III. Pathogenesis

1. UV-induced apoptosis of keratinocytes → surface expression of autoantigens (Ro/SSA, La/SSB, dsDNA)
2. TLR7/TLR9 activation → plasmacytoid dendritic cells (PDC) produce IFN-α in large quantities
3. IFN-α amplification loop: monocytes differentiate into PDCs → more IFN-α production
4. Chemokine release (CXCL9, CXCL10) → recruitment of CXCR3+ CD4+ and CD8+ T cells into skin
5. Cytotoxic T lymphocytes (granzyme B, TIA1) → basal keratinocyte destruction → interface dermatitis
6. B cell activation → autoantibody production (ANA, anti-Ro, anti-dsDNA)
7. Immune complex deposition at DEJ → complement activation → tissue damage

— Rook's Dermatology, 9e (Fig. 41.1, Pathogenesis of Lupus Erythematosus)

IV. Clinical Features by Subtype

A. Acute CLE (ACLE)

• Localized ACLE: Bilateral, symmetric malar/"butterfly" erythema — spares nasolabial folds
• Transient, follows sun exposure; resolves without scarring (may leave dyspigmentation)
• Range: mild erythema → intense oedema, telangiectasia, erosions, poikiloderma
• Generalized ACLE: photodistributed morbilliform eruption on trunk and extremities; knuckles typically spared (distinguishes from dermatomyositis)
• Associated with active SLE; linked to anti-dsDNA antibodies and lupus nephritis
• Rowell syndrome: EM-like lesions in lupus patients
• Rarely: TEN-like presentation with extensive epidermal necrosis

— Rook's Dermatology, 9e, p. 815; Andrews' Diseases of the Skin, p. 189

B. Subacute CLE (SCLE)

• Described by Sontheimer, Thomas, and Gilliam (1979)
• Most common in White women, age 15–40; accounts for 10–15% of CLE
• Photodistribution: sides of face, upper trunk, extensor upper extremities; midface typically spared
• Two morphologic patterns:
  • Annular: raised pink-red borders with central clearing and fine scale
  • Papulosquamous: psoriasiform or eczematous appearance
• Lesions are minimally palpable (sparse infiltrate), resolve with dyspigmentation/hypopigmentation but no scarring
• ~30% drug-induced SCLE: hydrochlorothiazide (first reported), terbinafine, TNF inhibitors, antiepileptics, PPIs, immune checkpoint inhibitors (pembrolizumab, nivolumab)
• Anti-Ro/SSA antibodies in ~70% — hallmark serological association
• ~15–20% meet SLE criteria (usually mild, cutaneous/mucosal)

— Andrews' Diseases of the Skin; Rook's Dermatology, 9e, p. 812

C. Chronic CLE — Discoid LE (DLE)

• Most common CCLE subtype
• Lesions begin as dull-red macules or indurated plaques → develop adherent scale with follicular plugging (carpet-tack sign on underside of scale) → progress to atrophy, scarring, and dyspigmentation

1. Localized DLE (above the neck)

• Sites: malar areas, bridge of nose, lower lip, scalp, concha of ear, external canal
• Scalp: erythematous patches → white depressed scarring alopecia (permanent)
• Lips: grey/red hyperkeratotic erosions with narrow red inflammatory zone
• Active disease signs: perifollicular erythema, easily extractable anagen hairs
• 24% have mucosal involvement (mouth, nose, eye, vulva)
• Rarely: SCC may arise in long-standing DLE lesions (Marjolin's ulcer equivalent)

2. Generalized DLE (below the neck also)

• Higher risk of laboratory abnormalities (elevated ESR, ANA, leukopenia)
• Greater risk of progression to SLE

3. Hypertrophic/Verrucous DLE

• Intensely hyperkeratotic lesions on extensor arms, face, upper trunk
• Can mimic keratoacanthoma or SCC

4. Risk of progression to SLE

• Localized DLE → SLE: ~5–15% (over 8–10 years)
• Generalized DLE: higher risk (~28%)
• Childhood DLE: up to 26% eventually meet SLE criteria

— Andrews' Diseases of the Skin, p. 188; Rook's Dermatology, p. 810

D. LE Tumidus

• Firm erythematous plaques — no epidermal change (no scale, no follicular plugging)
• Intense perivascular and periadnexal infiltrate + prominent mucin deposition in dermis
• High photosensitivity; reproducible by phototesting
• Resolves without scarring, atrophy, or dyspigmentation — best prognosis of all CLE subtypes
• Low prevalence of SLE and serological abnormalities; considered by some to overlap with Jessner's lymphocytic infiltrate

E. LE Panniculitis (Lupus Profundus)

• Firm, deep subcutaneous nodules/indurated plaques — upper arms, face, scalp, upper trunk, breasts
• Overlying skin may be normal or have concurrent DLE (lupus profundus = DLE + panniculitis)
• Resolves with disfiguring lipoatrophy/depressed "dells"
• Affects women aged 20–45
• Critical differential: subcutaneous panniculitis-like T-cell lymphoma (SPTCL) — biopsy mandatory

F. Chilblain Lupus

• Red/dusky purple papules and plaques on toes, fingers, nose, ears, lower legs
• Precipitated/exacerbated by cold moist conditions
• Familial form: mutations in TREX1 or SAMHD1 (DNA exonuclease genes)
• Lesions evolve towards DLE morphology with time

V. Histopathology

Interface Dermatitis — Shared Pattern

• DLE: CD4+ T lymphocytes and macrophages; dense infiltrate extends into deep dermis/subcutis; chronic scarring DLE → fibroplasia replaces infiltrate
• LE tumidus: perivascular/periadnexal infiltrate + abundant mucin; no epidermal changes
• LE panniculitis: lymphoid nodules in subcutaneous septa, fat lobule necrosis, fibrinoid/hyaline degeneration of lipocytes, lipomembranous change

— Fitzpatrick's Dermatology, 9e, p. 1080; Andrews' Diseases of the Skin

VI. Immunofluorescence

Direct Immunofluorescence (DIF) — Lupus Band Test (LBT)

• Positive: granular/linear deposits of IgG, IgA, IgM, C3, C4, C1q at the dermoepidermal junction (DEJ)
• Lesional skin LBT positive:
  • DLE: ~90%
  • SCLE: ~60%
  • ACLE: ~70%
• Non-lesional (sun-exposed) skin LBT positive: strongly suggests SLE (~80% in SLE)
• Non-lesional (non-sun-exposed) skin LBT positive: highly specific for SLE
• False negatives occur; must be interpreted with clinical and histological context

Autoantibodies (Serology)

VII. Investigations

• CBC: leukopenia, lymphopenia, thrombocytopenia (SLE)
• ESR, CRP, complement (C3, C4): disease activity
• Urinalysis + 24h protein: nephritis screen
• ANA (screening) → if positive: anti-dsDNA, anti-Ro, anti-La, anti-Sm, anti-histone
• Skin biopsy: H&E + DIF (lesional + non-lesional samples)
• Phototesting: LE tumidus reproducibility
• ECHO: if Ro+ mother — screen neonate for congenital heart block

VIII. Treatment

General Measures (All CLE)

• Strict photoprotection: broad-spectrum sunscreen (SPF ≥50+, UVA+UVB), physical blockers (zinc oxide, titanium dioxide), protective clothing, UV avoidance
• Stop offending drugs (in SCLE)
• Smoking cessation (reduces HCQ efficacy)

Topical Therapy

• Topical corticosteroids (medium-to-high potency): first-line for localized disease
• Topical calcineurin inhibitors (tacrolimus, pimecrolimus): face and flexures; steroid-sparing
• Intralesional triamcinolone: recalcitrant DLE lesions

Systemic Therapy

IX. Special Situations

• Neonatal LE: transplacentally acquired maternal anti-Ro/SSA → neonatal annular rash (resolves ~6 months), hepatitis, thrombocytopenia, congenital heart block (permanent, most serious complication)
• Drug-induced SCLE: resolves on stopping offender; may persist for months
• SLE in DLE: ~5–15% localized; ~28% generalized; monitor with annual urinalysis, ANA, CBC
• SCC in DLE: rare but aggressive; regular follow-up of chronic DLE scars

X. Differential Diagnosis

Conclusion

Porphyria Cutanea Tarda (PCT)

Introduction

I. Heme Biosynthesis — Background

• Bone marrow (~85% — for haemoglobin synthesis)
• Liver (~15% — for cytochrome P450)

— Rook's Dermatology, 9e (Fig. 49.1); Harrison's 22e, p. 3391

II. Classification of PCT

III. Pathogenesis

1. UROD deficiency (acquired or inherited) → impaired conversion of uroporphyrinogen III → coproporphyrinogen III
2. Accumulation of highly carboxylated uroporphyrins and heptacarboxylate porphyrins in the liver
3. These porphyrins are absorbed into the circulation and deposited in the skin
4. UV light (Soret band ~400–410 nm) activates porphyrins → generation of reactive oxygen species (ROS) and singlet oxygen
5. ROS → oxidative damage to proteins, lipids, and the dermoepidermal junction → subepidermal blistering
6. The formation of a uroporphomethene inhibitor in the liver (requiring iron + oxidative stress) is the proximate cause of UROD inhibition in sporadic PCT — explaining why iron overload is central to pathogenesis

IV. Precipitating and Susceptibility Factors ("The Multiple Hit Hypothesis")

"Multiple susceptibility factors that appear to act synergistically can be identified in individual patients." — Harrison's 22e, p. 3391

V. Clinical Features

A. Cutaneous Manifestations (Sun-Exposed Areas — Dorsal Hands, Forearms, Face)

1. Skin fragility and blistering (Photo-Mechanobullous eruption)
   • Non-inflammatory tense vesicles and bullae on dorsal hands/forearms
   • Rupture easily → erosions, crusts → heal with atrophic scarring
   • Milia (small white epidermal cysts) form in resolving blisters — especially on dorsal hands and fingers
2. Hypertrichosis
   • Fine, dark hair over the cheeks, temples, and periorbital areas
   • Especially distressing in women; one of the most characteristic features
3. Hyperpigmentation
   • Diffuse, brown/slate-grey hyperpigmentation in sun-exposed areas (face, neck, hands)
   • Pink-to-violaceous tint of the face and periorbital area (due to dermal porphyrin deposition)
   • In women: melasma-like facial hyperpigmentation
4. Sclerodermatoid/Morpheiform changes
   • Waxy, indurated thickening of skin on the back of neck, preauricular areas, thorax, fingers, scalp
   • Associated scarring alopecia on scalp
   • Directly correlated with urinary uroporphyrin levels
5. Distribution specifics
   • Dorsal hands and forearms: primary site (both sexes)
   • Face, ears: commonly involved
   • Legs (shins, dorsal feet): predominantly in women

B. Systemic Associations

• Liver disease: chronic hepatitis, cirrhosis; elevated liver enzymes
• Hepatocellular carcinoma (HCC): 3.5× increased risk; hepatic imaging mandatory
• Diabetes mellitus (Type 2): ~15–20% of PCT patients; typically develops ~1 decade after PCT onset
• Lupus erythematosus: SLE and CLE co-occurrence reported

VI. Histopathology

Light Microscopy

• Subepidermal, cell-poor (pauci-inflammatory) blisters — characteristic feature
• Festooning of dermal papillae: rigid, intact papillae project upward into the blister floor — most distinctive histological sign of PCT
• The festooning results from deposition of PAS-positive, diastase-resistant material (thickened vascular walls and DEJ) — this rigidity prevents papillae from being stripped off into the blister roof
• Thickened walls of superficial dermal blood vessels with PAS-positive hyaline deposits
• Caterpillar bodies (linear PAS-positive deposits in roof of blister) — particularly prominent
• Mild superficial perivascular lymphohistiocytic infiltrate
• Solar elastosis commonly present in background dermis

Immunofluorescence (DIF)

• IgG, IgM, C3 deposited in a homogeneous pattern around superficial dermal blood vessels and at the DEJ
• This perivascular immunoglobulin pattern differentiates PCT from other subepidermal bullous disorders

— Rook's Dermatology, 9e, p. 948; Andrews' Diseases of the Skin, p. 605

VII. Investigations and Diagnosis

Urine

• Pink-red fluorescence of urine under Wood's lamp (coral-red/pink)

Faeces

• Isocoproporphyrins elevated — pathognomonic for hepatic UROD deficiency
• Distinguishes PCT from VP (variegate porphyria) and HCP

Plasma

• Elevated plasma porphyrins — used for monitoring
• Fluorometric scanning at neutral pH: PCT shows peak at ~619 nm; VP shows peak at ~624–626 nm (rapid bedside distinction)

Blood

• RBC UROD activity: reduced (~50% of normal) in Type II; normal in Type I
• Serum ferritin: elevated (iron overload marker; treatment target)
• Serum iron, transferrin saturation: elevated
• LFTs: frequently abnormal
• HFE mutation screening: C282Y, H63D
• ANA, anti-Ro: rule out associated lupus
• Anti-HCV, HIV serology
• Blood glucose, HbA1c

Skin Biopsy

• H&E: subepidermal cell-poor blister with festooning
• DIF: perivascular IgG/IgM/C3

VIII. Differential Diagnosis

IX. Treatment

Step 1: Remove Precipitating Factors

• Abstain from alcohol
• Stop oestrogens, iron supplements, offending drugs
• Photoprotection: broad-spectrum sunscreen (SPF ≥50+), physical barrier, protective clothing, UV avoidance

Step 2: Specific Therapy

A. Phlebotomy (First-line, Most Effective)

• Goal: Reduce excess hepatic iron until serum ferritin reaches lower limit of normal (~20 ng/mL)
• Regimen: Remove 450 mL (~1 unit) of blood every 1–2 weeks
• Typically requires 5–6 phlebotomies in uncomplicated PCT; more in concurrent hemochromatosis
• Monitor: plasma porphyrins (normalize after ferritin target is reached), Hb, haematocrit
• Biochemical remission in ~6–7 months; may last years
• Relapse: treat with further phlebotomy sessions

B. Low-Dose Antimalarials (Alternative / Adjunct)

• Used when phlebotomy is contraindicated (severe anaemia, cardiac disease, polycythaemia vera)
• Mechanism: Antimalarials complex with porphyrins in hepatocytes → enhanced biliary/urinary excretion
• Regimen:
  • Chloroquine phosphate: 125 mg twice weekly (not standard dose — standard doses cause hepatotoxic reaction with acute porphyrin release)
  • Hydroxychloroquine: 100–200 mg twice weekly
• Equivalent efficacy to phlebotomy; remission in ~6–7 months
• Can be combined with phlebotomy in difficult/refractory cases
• Caution: Full therapeutic doses cause severe transient exacerbation of skin lesions + hepatotoxicity

C. HCV Treatment

• Direct-acting antivirals (DAAs) for HCV → documented PCT remission with viral cure
• Now considered first-line treatment in HCV-positive PCT patients

D. Special Situations

X. Monitoring and Prognosis

• Plasma porphyrin levels every 6–12 months after remission (early relapse detection)
• Liver imaging (USS/CT): screen for hepatocellular carcinoma (3.5× increased risk)
• Diabetes surveillance: annual fasting glucose/HbA1c
• Iron studies: after phlebotomy course
• Prognosis: Excellent with treatment; complete biochemical and clinical remission achievable; relapses respond to repeat therapy

Summary Table — Key Diagnostic Points

Conclusion

Skin Manifestations of Diabetes Mellitus and Hypothyroidism

PART A: SKIN MANIFESTATIONS OF DIABETES MELLITUS (DM)

Introduction

1. Dermatoses with direct pathogenic association to DM
2. Dermatoses with frequent but non-specific association to DM
3. Cutaneous complications of DM therapy

I. Dermatoses Specifically Associated with DM

1. Necrobiosis Lipoidica Diabeticorum (NLD)

• Epidemiology: Affects ~0.3% of all DM patients; >2% in Type 1 DM; F:M = 3:1; mean age 34 years overall; 22 years in insulin-dependent DM
• 60% occur in insulin-dependent (Type 1) DM; 20% in pre-diabetic states; 15% precede DM onset by ~2 years
• Clinical features:
  • Begins as small, sharply bordered red papules with slight scale
  • Evolves into oval/round, well-defined plaques with waxy, glazed surface
  • Centre: depressed, sulphur-yellow with prominent telangiectasias
  • Peripheral rim: violaceous/pink-red active border
  • Ulceration in ~33% of cases
  • Rarely: SCC may arise in chronic ulcers (Marjolin's ulcer-type)
• Site: Anterior shins (bilateral in 85%); less commonly forearms, trunk, face
• Histology: Layered palisaded granulomas with pale-pink degenerated (necrobiotic) collagen alternating with histiocytes; whole reticular dermis + subcutis involved; lymphocytes, histiocytes, multinucleate giant cells, plasma cells; no increased mucin (unlike GA); overlying epidermis thinned with loss of rete ridges
• Treatment: Control of DM; superpotent topical corticosteroids ± occlusion; intralesional triamcinolone into active border (not yellow centre); topical calcineurin inhibitors; aspirin + dipyridamole; biologic agents (TNF inhibitors) in refractory cases

— Andrews' Diseases of the Skin, 12e, p. 623; Rook's Dermatology, 9e

2. Diabetic Dermopathy ("Shin Spots")

• Most common skin finding in DM (~55% of diabetics)
• Clinical features: Small, round-to-oval, brown atrophic macules and patches on the shins (pretibial area)
• Begin as dull-red papules → atrophic pigmented scars
• Bilateral but asymmetric; lesions persist for months then fade
• Pathogenesis: Trauma + altered wound healing due to microangiopathy
• Not specific to DM but highly characteristic; often indicates microvascular disease
• Histology: Haemosiderin deposition, vessel wall thickening, lymphocytic infiltrate

3. Diabetic Bullae (Bullosis Diabeticorum)

• Tense, non-inflammatory bullae arising spontaneously (without trauma) on the lower extremities — feet, legs; occasionally hands
• Intraepidermal or subepidermal; heal without scarring over 2–6 weeks
• Pathogenesis: Uncertain; microangiopathy, reduced threshold for suction blistering
• Must be distinguished from PCT, pseudoporphyria, bullous pemphigoid
• Treatment: Aspiration of bullae; local wound care; glycaemic control

4. Diabetic Cheiroarthropathy (Limited Joint Mobility Syndrome / Stiff Hand Syndrome)

• Thickened, waxy skin with limited joint mobility of the hands
• Starts at the 5th digit, progressing radially → flexion contractures
• Prayer sign (inability to approximate palmar surfaces of both hands)
• Pathogenesis: Increased glycosylation of collagen → cross-linking → thickening and rigidity
• Associated with retinopathy, nephropathy, and duration (not control) of DM
• Also called diabetic scleredema or digital sclerosis

5. Acanthosis Nigricans (AN)

• Velvety, hyperpigmented, rugose thickening of the skin in intertriginous and flexural areas (neck, axillae, groin, antecubital fossae)
• Cutaneous marker of insulin resistance → excess circulating insulin activates IGF-1 receptors on keratinocytes → proliferation
• Found in Type 2 DM, metabolic syndrome, obesity, PCOS
• Skin tags (acrochordons) often co-exist
• Rarely, may be paraneoplastic (AN maligna — severe, rapidly progressive)
• Treatment: Weight loss, metformin; cosmetic options (topical retinoids, AHAs)

6. Eruptive Xanthomas

• Sudden eruption of red-yellow papules with surrounding erythematous halo
• Located on buttocks, extensor surfaces (knees, elbows), trunk
• Occur in poorly controlled DM with severe hypertriglyceridaemia (>1000 mg/dL)
• Histology: Foam cells (lipid-laden macrophages) in the dermis
• Resolve with glycaemic control and triglyceride reduction
• Marker of cardiovascular risk

7. Granuloma Annulare (Disseminated Type)

• Annular, skin-coloured to erythematous plaques composed of peripheral papules with central clearing
• Localised GA is not specifically associated with DM; disseminated/perforating GA has controversy-laden but recognised association
• Trunk, extremities; adults > 40 years
• Histology: Palisaded granulomas with central mucin (contrasts with NLD)

8. Scleredema Diabeticorum

• Non-pitting woody induration of the skin of the upper back, neck, and shoulders
• Histology: Swollen collagen bundles separated by mucin (hyaluronic acid)
• Predominantly in obese, middle-aged men with long-standing, poorly controlled Type 2 DM
• Differs from classic scleredema of Buschke (post-streptococcal)
• Resistant to treatment; glycaemic control may partially help

9. Neuropathic Ulcers (Diabetic Foot)

• Non-painful plantar ulcers at pressure points (metatarsal heads, heel, great toe)
• Surrounded by characteristic hyperkeratotic rim
• Result of peripheral sensory neuropathy + impaired wound healing + microangiopathy
• Charcot foot: erythema, warmth, swelling, "rocker bottom" deformity
• Management: Offloading, debridement, wound care, glycaemic control, antibiotics if infected

10. Perforating Dermatoses

• Kyrle disease (acquired perforating dermatosis) in DM + renal failure
• Hyperkeratotic papules and plaques with central keratinous plug
• Pathogenesis: Transepidermal elimination of altered dermal material

II. Other Dermatoses with DM Association

PART B: SKIN MANIFESTATIONS OF HYPOTHYROIDISM

Introduction

I. Changes in General Skin Texture and Colour

1. Dry, Coarse, Rough Skin (Xerosis)

• Decreased core temperature → peripheral vasoconstriction → pale, cool, dry skin
• Reduced sweating (eccrine gland hypofunction)
• Stratum corneum poorly hydrated
• May mimic acquired ichthyosis — distinguished from ichthyosis vulgaris by generalised distribution and association with systemic symptoms
• Histology: Thin epidermis, hyperkeratosis, follicular plugging

2. Myxedema

• The most classic and defining skin finding of hypothyroidism
• Pathogenesis: Dermal accumulation of glycosaminoglycans — hyaluronic acid and chondroitin sulphate — which bind water, causing brawny, non-pitting oedema
• Generalised myxoedema: boggy, doughy, non-pitting, waxy induration of the skin
• Facial myxedema: broadened nose, thickened lips, puffy eyelids, macroglossia (large, smooth, clumsy tongue)
• Extremities particularly prominent
• Resolves with adequate thyroxine replacement

3. Yellow-Orange Skin Discoloration (Pseudojaundice / Carotenoderma)

• Accumulation of β-carotene in the stratum corneum
• Due to diminished hepatic conversion of β-carotene to vitamin A (reduced hepatic enzyme activity)
• Most prominent on palms, soles, nasolabial folds
• Sclerae are spared — key differentiating feature from true jaundice (bilirubin stains sclerae)

4. Pallor

• Due to peripheral vasoconstriction, anaemia (often coexists), and dermal mucinous infiltration reducing transparency

5. Easy Bruising

• Due to capillary fragility and factor VIII deficiency

II. Hair Changes

III. Nail Changes

• Thin, brittle, striated nails with longitudinal and transverse ridging
• Slow nail growth
• Onycholysis (rare — more characteristic of hyperthyroidism)
• Koilonychia (rare)

IV. Acquired Palmoplantar Keratoderma

• Diffuse, waxy thickening of palms and soles
• Responds well to thyroxine replacement
• Rare but recognised manifestation of hypothyroidism

V. Wound Healing

• Impaired wound healing — reduced cell proliferation, decreased collagen synthesis, reduced angiogenesis
• Wounds heal slowly; sutures may need to remain longer

VI. Associated Autoimmune Dermatoses (Hashimoto Thyroiditis)

VII. Thyroid Dermopathy (Pretibial Myxedema — NOTE: associated with Hyperthyroidism/Graves disease, not hypothyroidism)

• This is a hyperthyroid manifestation — but included here for completeness and as a common exam pitfall
• Classic manifestation of Graves disease (autoimmune hyperthyroidism)
• Occurs in <5% of Graves patients; almost always with moderate-to-severe ophthalmopathy
• Pathogenesis: TSH receptor antibodies stimulate dermal fibroblasts expressing TSH receptors → glycosaminoglycan (GAG) deposition
• Clinical features: Bilateral, painless, non-pitting waxy nodules/plaques over the anterior and lateral shin; orange-peel (peau d'orange) texture; may extend to feet (elephantiasic form)
• 4 clinical forms: non-pitting oedema, plaque type, nodular type, elephantiasic type
• Associated with thyroid acropachy: periostitis, digital clubbing, acral soft-tissue swelling — Graves triad (ophthalmopathy + dermopathy + acropachy)
• Treatment: Topical very-high-potency corticosteroids under occlusion; may persist even after treatment of hyperthyroidism

Summary Comparison Table

Conclusion

Nails in Psoriasis

Introduction

I. Classification by Anatomical Site

— Fitzpatrick's Dermatology, 9e (Table 28-1)

II. Individual Nail Signs — Pathogenesis and Clinical Features

1. Nail Pitting ⭐ (Most Common Sign)

• Most common nail finding in psoriasis; highly characteristic
• Pathogenesis: Small foci of parakeratosis in the proximal nail matrix (which forms the dorsal/superficial nail plate) → these parakeratotic cells are shed as the nail plate grows distally → pits form on the nail plate surface
• Morphology: Pits are large, deep, irregularly scattered (random pattern) — may be covered by whitish, easily detachable scale
• Range from 0.5–2.0 mm; single or multiple
• Key differential: Alopecia areata pits are small, shallow, geometrically arranged (grid/rows); psoriatic pits are large, deep, random

2. Oil Drop Sign / Salmon Patch ⭐ (Most Specific Sign)

• Most specific and nearly pathognomonic for psoriasis
• Pathogenesis: Psoriasiform hyperplasia, parakeratosis, microvascular changes, and neutrophil trapping in the nail bed → discoloration visible through transparent nail plate
• Morphology: Irregular, translucent, yellow-orange to red-brown discoloration seen through the nail plate; often extends toward the hyponychium distally
• Also called "salmon patch" (when reddish) or "oil drop" (when yellow-orange)
• Unlike pitting, oil spotting is considered nearly specific for psoriasis

3. Onycholysis

• Separation of the nail plate from the nail bed, starting distally and progressing proximally
• Pathogenesis: Parakeratosis of the distal nail bed → structural disruption
• Distinctive feature in psoriasis: Onycholysis is surrounded by an erythematous (red) border — this distinguishes psoriatic onycholysis from traumatic or fungal onycholysis (which have no erythematous border)
• May produce a "white" appearance due to air under the plate

4. Subungual Hyperkeratosis

• Accumulation of keratinous material under the nail plate (nail bed + hyponychium)
• Results from hyperkeratosis of the nail bed due to parakeratosis
• Often accompanies onycholysis
• Makes nail plate appear thickened, raised, and crumbly
• Important: In toenails, subungual hyperkeratosis can be indistinguishable from onychomycosis → requires mycological examination of nail clippings

5. Splinter Haemorrhages

• Fine, linear dark-red streaks running longitudinally under the nail plate
• Pathogenesis: Increased capillary fragility in the thin suprapapillary plate of the psoriatic nail bed → bleeding
• Common but not specific (also seen in endocarditis, trauma, lichen planus)

6. Leukonychia

• White discoloration of the nail plate
• Due to psoriatic involvement of the intermediate nail matrix → defective keratinisation producing opaque white areas
• Irregular, non-geometric pattern

7. Red Spots in the Lunula (Erythema of the Lunula)

• Irregular erythematous macular discoloration of the lunula (pale half-moon)
• Due to psoriatic involvement of the distal matrix and underlying capillary changes
• Relatively uncommon but characteristic

8. Onychodystrophy / Crumbling Nail

• When the entire nail matrix is involved → whitish, crumbly, poorly adherent nail plate
• Severe onychodystrophy (total destruction of nail architecture) is strongly associated with psoriatic arthritis

9. Beau's Lines

• Transverse grooves/depressions across the nail plate
• Due to transient arrest of nail matrix activity during acute flares of psoriasis

10. Anonychia

• Complete loss of the nail plate
• Rare; seen in severe pustular psoriasis (acrodermatitis continua of Hallopeau type)

III. Nail Matrix Disease vs. Nail Bed Disease

— Harrison's Principles of Internal Medicine, 22e, p. 2931; Rook's Dermatology, 9e

IV. Clinical Relevance

• Nail psoriasis may be the only manifestation of psoriasis in some patients (isolated nail psoriasis)
• ~52% of patients report pain from nail involvement; 14% have major restrictions in daily activities
• Nail psoriasis is a biomarker for PsA: patients with nail involvement have higher incidence of PsA; nail involvement affects ~90% of PsA patients
• Koebner phenomenon can worsen nail symptoms (vigorous removal of subungual debris is an aggravating factor)
• Toenail psoriasis is often clinically indistinguishable from onychomycosis → nail clipping for KOH/fungal culture/nail plate histology is mandatory before treatment

V. Differential Diagnosis

VI. Treatment (Brief Overview for Completeness)

• Topical: High-potency corticosteroids (clobetasol) ± occlusion; calcipotriol; tazarotene — for mild/few nails
• Intralesional: Triamcinolone acetonide (2.5–10 mg/mL) into nail matrix (proximal fold) — for matrix disease; nail bed (periungual) — for bed disease
• Systemic: Methotrexate, cyclosporine, acitretin — for extensive nail + skin psoriasis
• Biologics: TNF-inhibitors (adalimumab, etanercept), IL-17/23 inhibitors (secukinumab, ixekizumab, guselkumab) — most effective for nail psoriasis, especially with PsA
• Nail avulsion: For refractory onycholysis + hyperkeratosis
• Nail protection: Avoid trauma, short nails, protective gloves

Conclusion