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Diabetes Mellitus - Complete Lecture Notes

PA 31.5: Classification, Epidemiology, Etiology, Pathogenesis, Pathology, Clinical/Laboratory Features, Complications, and Progression

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1. DEFINITION

Harrison's Principles of Internal Medicine 22E, p. 3292

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2. CLASSIFICATION

• Latent autoimmune diabetes in adults (LADA): A slow-onset autoimmune form misclassified as T2DM in adults; positive for GAD65 antibodies.
• Maturity-onset diabetes of the young (MODY): Monogenic, autosomal dominant, presents in youth; does NOT require insulin.
• Ketosis-prone T2DM: Found in some African-origin populations; episodic DKA but with preserved beta-cell function between episodes.

Textbook of Family Medicine 9e, p. 964

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3. EPIDEMIOLOGY

• Global burden: The WHO estimates over 347 million people worldwide have diabetes; 90% involve T2DM.
• Projected to rise to 439 million (7.7% of global population) by 2030.
• T1DM accounts for ~5-10% of all DM cases; peak onset is childhood/adolescence but can occur at any age.
• T2DM prevalence is rising due to the global increase in obesity, physical inactivity, and aging populations.
• GDM affects ~7% of all pregnancies; women with GDM have a 35-60% risk of developing T2DM within 10 years.
• Diabetes is a leading cause of blindness, renal failure, lower-limb amputation, and cardiovascular mortality worldwide.
• Sex differences: Women with DM have a sixfold greater risk of dying from cardiovascular disease (CVD) compared to women without DM. Premenopausal women with DM lose their natural cardioprotective advantage.

Textbook of Family Medicine 9e, p. 964; Harrison's 22E, p. 3292

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4. ETIOLOGY

Type 1 DM

• Autoimmune destruction of pancreatic beta-cells, mediated by CD8+ and CD4+ T lymphocytes and autoantibodies:
  • Islet cell antibodies (ICA)
  • Anti-glutamic acid decarboxylase (GAD65) antibodies
  • Insulin autoantibodies (IAA)
  • Anti-IA-2 (tyrosine phosphatase) antibodies
• Genetic susceptibility: Strongly associated with HLA-DR3 and HLA-DR4 alleles (HLA region accounts for ~40% of genetic risk). Non-HLA genes (INS, CTLA4, PTPN22) also contribute.
• Environmental triggers: Viral infections (enterovirus, Coxsackie B4), dietary factors (bovine milk protein exposure in early life), gut microbiome alterations.
• The process is gradual - most beta-cells are lost before clinical symptoms appear (~80-90% destruction required).

Type 2 DM

• Polygenic disorder with strong environmental interaction.
• Two core defects:
  1. Peripheral insulin resistance (skeletal muscle, liver, adipose tissue) - the first detectable abnormality
  2. Progressive beta-cell failure - compensatory hyperinsulinemia eventually gives way to insufficient insulin secretion
• Genetic factors: >400 genetic variants identified; major risk genes include TCF7L2, KCNJ11, PPARG, SLC30A8.
• Environmental activators (from Table 34-4 of Family Medicine textbook):
  • Advanced age (DNA methylation changes, chronic inflammation)
  • Obesity - especially visceral/central adiposity
  • Physical inactivity
  • Obstructive sleep apnea and sleep disorders (circadian misalignment affects glucose-insulin metabolism)
  • Mental illness (depression, schizophrenia) - linked to inflammation, inactivity, and dopaminergic pathways
  • Second-hand smoke exposure (induces adipocyte hypertrophy, insulin resistance, chronic pancreatic inflammation)
  • History of physical/sexual abuse (Nurses' Health Study II - moderate physical abuse: 26% higher diabetes risk)
  • Late chronotype (skipping breakfast, high caloric intake at dinner)

Textbook of Family Medicine 9e, p. 968

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5. PATHOGENESIS

Normal Glucose Homeostasis

• Insulin: lowers glucose by stimulating uptake in skeletal muscle/fat, suppressing hepatic glucose output, limiting lipolysis
• Glucagon: raises glucose via hepatic glycogenolysis and gluconeogenesis
• Counterregulatory hormones (catecholamines, cortisol, growth hormone): activated when glucose drops >20 mg/dL
• The body stores ~450 g glucose; brain requires 125 g/day; liver contributes 50% via glycogenolysis and 30% via gluconeogenesis

Pathogenesis of Type 1 DM

Genetic predisposition (HLA + non-HLA genes)
        ↓
Environmental trigger (virus, dietary antigen)
        ↓
Immune activation → T-cell-mediated insulitis (CD8+ cytotoxic T cells destroy beta cells)
        ↓
Progressive beta-cell loss (asymptomatic for years)
        ↓
~80-90% beta-cell destruction → clinical onset (hyperglycemia, polyuria/polydipsia)
        ↓
Absolute insulin deficiency → uninhibited lipolysis → FFA → ketogenesis → DKA risk

• Insulin deficiency leads to unrestrained hepatic gluconeogenesis and glycogenolysis
• Loss of insulin causes lipolysis → free fatty acids → hepatic ketone body production (acetoacetate, beta-hydroxybutyrate, acetone)
• This is the metabolic basis of diabetic ketoacidosis (DKA)

Pathogenesis of Type 2 DM

Genetic susceptibility + Obesity/Lifestyle factors
        ↓
Peripheral insulin resistance (skeletal muscle, liver, adipose)
        ↓
Compensatory hyperinsulinemia (beta-cells work harder)
        ↓
Glucotoxicity + Lipotoxicity → progressive beta-cell exhaustion and apoptosis
        ↓
Relative then absolute insulin insufficiency → frank hyperglycemia
        ↓
"Glucose toxicity" cycle: hyperglycemia further impairs insulin secretion

• Increased circulating free fatty acids (from adipose tissue) impair insulin signaling via protein kinase C and IRS-1 phosphorylation
• Adipokine imbalance: decreased adiponectin, increased TNF-alpha, IL-6, resistin
• Ectopic fat deposition in liver (hepatic steatosis) and muscle

• GLP-1 (glucagon-like peptide-1) is normally released by intestinal L-cells in response to meals and potentiates insulin secretion
• In T2DM, both the secretion of GLP-1 and the beta-cell response to GLP-1 are impaired ("incretin defect")

• GLUT4 (insulin-sensitive glucose transporter in muscle and fat) is impaired at rest in T2DM but is enhanced by muscle contractions during exercise - this is the basis for exercise as therapy

Textbook of Family Medicine 9e, pp. 968-970

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6. PATHOLOGY

Pancreatic Histopathology

• Insulitis: In T1DM, islets show dense lymphocytic infiltration predominantly by CD8+ T cells; seen early in the disease course; in established T1DM the islets are atrophic and devoid of beta-cells
• IAPP (amylin) deposition: In T2DM, amyloid derived from IAPP co-secreted with insulin accumulates in islets; this contributes to progressive beta-cell dysfunction and apoptosis

Vascular Pathology (basis of chronic complications)

1. Microvascular: Thickening of capillary basement membranes - the hallmark of diabetic microangiopathy. Seen in retina, kidney glomeruli, and peripheral nerves.
2. Macrovascular: Accelerated atherosclerosis due to:
   • Advanced glycation end-products (AGEs)
   • Oxidative stress
   • Endothelial dysfunction
   • Dyslipidemia (high TG, low HDL)
   • Hypertension
3. Diabetic nephropathy histology:
   • Diffuse glomerulosclerosis (most common) - diffuse increase in mesangial matrix
   • Nodular glomerulosclerosis - Kimmelstiel-Wilson nodules (PAS-positive nodular deposits in the mesangium) - pathognomonic
   • Arteriolar hyalinosis (afferent > efferent)
   • Tubular atrophy, interstitial fibrosis in advanced disease

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7. CLINICAL FEATURES

Symptoms of Acute Hyperglycemia (the "classic triad")

• Polyuria - osmotic diuresis from glucosuria (when glucose exceeds renal threshold ~180 mg/dL)
• Polydipsia - compensatory response to osmotic diuresis and dehydration
• Polyphagia - cellular "starvation" despite hyperglycemia (in T1DM especially)
• Weight loss - urinary caloric loss + muscle protein catabolism (T1DM > T2DM)
• Fatigue and weakness
• Blurred vision - from osmotic changes in lens water content (reversible with glycemic control)
• Frequent infections - vaginitis, fungal skin infections, recurrent UTIs, boils, impaired wound healing

Type 1 vs Type 2 Clinical Presentation

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8. LABORATORY FEATURES AND DIAGNOSIS

ADA Diagnostic Criteria (any one criterion is sufficient)

Pre-Diabetes Thresholds

Key Laboratory Tests in Management

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9. COMPLICATIONS

Acute Complications

A. Diabetic Ketoacidosis (DKA) - primarily T1DM

• Precipitants: Infection (most common), insulin omission, new-onset T1DM, surgery/trauma, MI
• Pathophysiology: Absolute insulin deficiency → unrestrained lipolysis → FFA → hepatic ketogenesis (acetoacetate, beta-hydroxybutyrate) → anion gap metabolic acidosis
• Clinical triad: Hyperglycemia + ketonemia + metabolic acidosis
• Symptoms: Nausea, vomiting, abdominal pain, Kussmaul respiration (deep rapid breathing), fruity breath (acetone), altered consciousness
• Lab: Glucose >250 mg/dL, pH <7.3, bicarbonate <18 mEq/L, elevated ketones, anion gap >12
• Treatment: IV fluids, IV insulin infusion, potassium replacement (critical - hypokalemia kills)

B. Hyperosmolar Hyperglycemic State (HHS) - primarily T2DM (elderly)

• Glucose often >600 mg/dL, severe dehydration, no/minimal ketosis (enough insulin to prevent ketogenesis)
• Hyperosmolality → obtundation, seizures
• High mortality (~15%)

C. Hypoglycemia

• Most common acute complication, especially with insulin or sulfonylurea therapy
• Glucose <70 mg/dL (<54 mg/dL for Level 2 hypoglycemia)
• Symptoms: tremor, sweating, palpitations, confusion, seizures, coma
• In T1DM with "hypoglycemia unawareness," counterregulatory response is blunted - silent and dangerous

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Chronic Complications

Microvascular Complications (due to hyperglycemia-driven basement membrane thickening)

• Leading cause of end-stage renal disease (ESRD) in developed countries
• Stages: Hyperfiltration (increased GFR) → microalbuminuria → macroalbuminuria → declining GFR → ESRD
• Key histologic lesion: Kimmelstiel-Wilson nodular glomerulosclerosis
• Screening: Annual UACR and eGFR
• Treatment: ACE inhibitors/ARBs (reduce proteinuria and slow progression); SGLT-2 inhibitors (renoprotective)

• Most common cause of new-onset blindness in working-age adults
• Stages:
  • Non-proliferative (NPDR): Microaneurysms, hemorrhages, hard exudates, cotton-wool spots, venous beading
  • Proliferative (PDR): Neovascularization (new fragile vessels that bleed) → vitreous hemorrhage, traction retinal detachment → blindness
  • Diabetic macular edema (DME): Can occur at any stage; causes central vision loss
• Screening: Annual dilated fundus exam
• Treatment: Laser photocoagulation (PDR), anti-VEGF injections (DME)

• Most common complication overall
• Types:
  • Distal symmetric polyneuropathy (DSP): "Glove-and-stocking" distribution; burning, tingling, numbness; loss of vibration/position sense; impaired ankle reflexes
  • Autonomic neuropathy: Gastroparesis (delayed gastric emptying → nausea, postprandial hypoglycemia, erratic glucose control), orthostatic hypotension, cardiac denervation (resting tachycardia, silent MI), erectile dysfunction, neurogenic bladder, sudomotor dysfunction (anhidrosis)
  • Focal/multifocal neuropathies: Cranial nerve palsies (CN III most common - pupil-sparing), diabetic amyotrophy (lumbosacral plexopathy)

Macrovascular Complications (accelerated atherosclerosis)

• Leading cause of death in diabetic patients
• T2DM patients have 2-4x increased risk of coronary artery disease (CAD), MI, stroke
• Women with DM lose their natural sex-related cardioprotection; have 6x greater CVD death risk
• Hypoglycemia in patients with ASCVD triggers proinflammatory, procoagulant, and proatherothrombotic responses (increases platelet aggregation, PAI-1, intravascular neutrophil activation)
• GLP-1 receptor agonists and SGLT-2 inhibitors have demonstrated direct cardiovascular benefit beyond glucose lowering

• PAD + neuropathy + infection = the triad driving lower limb amputations
• Diabetic foot: Charcot neuroarthropathy, non-healing ulcers, osteomyelitis

• Ischemic stroke risk 2-4x higher in DM
• Lacunar infarcts more common due to small vessel disease

Other Complications

• Infections: Impaired neutrophil function, poor microvascular perfusion; susceptibility to TB, fungal infections (mucormycosis in DKA), emphysematous pyelonephritis
• Cataracts: Osmotic lens changes; occur earlier and more frequently
• Glaucoma: Increased risk
• Non-alcoholic fatty liver disease (NAFLD/MASH): Closely linked to T2DM and insulin resistance

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10. PROGRESSION

Natural History of Type 1 DM

Pre-diabetes stage (months to years):
  ↓ Silent autoimmune destruction
  ↓ Positive autoantibodies (GAD, ICA, IAA)
  ↓ Normal glucose → impaired first-phase insulin secretion
  ↓
Clinical onset (~80-90% beta-cell loss):
  ↓ Polyuria, polydipsia, weight loss, DKA
  ↓
"Honeymoon period" (weeks to months):
  ↓ Partial beta-cell recovery; reduced insulin requirements
  ↓
Established T1DM:
  ↓ Complete insulin dependence
  ↓ Lifelong risk of hypoglycemia and DKA
  ↓
Chronic complications (typically after 10+ years of hyperglycemia):
  Retinopathy → Nephropathy → Neuropathy → CVD

Natural History of Type 2 DM

Insulin resistance (years before diagnosis):
  ↓ Compensatory hyperinsulinemia - euglycemia maintained
  ↓ Beta-cell "overstress" begins
  ↓
Pre-diabetes (IFG and/or IGT):
  ↓ 5-10% per year progress to frank T2DM
  ↓ High risk of CVD even at this stage
  ↓
Early T2DM:
  ↓ Post-prandial hyperglycemia (first-phase insulin secretion lost)
  ↓ Metformin + lifestyle usually sufficient
  ↓
Progressive T2DM:
  ↓ Fasting hyperglycemia (basal insulin secretion impaired)
  ↓ Multiple oral agents required
  ↓ Incretin therapy (GLP-1 RAs) / SGLT-2 inhibitors
  ↓
Advanced T2DM:
  ↓ Near-complete beta-cell failure → insulin therapy required
  ↓ Chronic complications established
  ↓
End-stage complications:
  ESRD (dialysis/transplant), blindness, amputations, ASCVD events

• Microvascular complications by 37%
• MI risk by 14%
• Stroke risk by 12%

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Summary Table: Key Distinguishing Features

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• Harrison's Principles of Internal Medicine, 22nd Edition (2025) - Chapters 415-417, pp. 3227-3292
• Textbook of Family Medicine, 9th Edition - Chapter 34, pp. 964-974
• Recent reviews: Aamodt & Powers, Diabetes Obes Metab (2025, PMID 40734585) on T1DM pathophysiology and classification

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DIABETES MELLITUS

PA 31.5 - Comprehensive Notes: Pathology | Medicine | Pharmacology

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PART 1: PATHOLOGY

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1.1 Pancreatic Pathology

Normal Islets of Langerhans

• Beta (β) cells (~60-70%): secrete insulin and amylin (IAPP)
• Alpha (α) cells (~20-25%): secrete glucagon
• Delta (δ) cells (~5%): secrete somatostatin
• PP cells: secrete pancreatic polypeptide

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Type 1 DM - Pancreatic Histopathology

1. Environmental trigger (viral, dietary) activates antigen-presenting cells
2. Autoantigens presented: GAD65, IA-2, pro-insulin peptides
3. CD8+ T cells infiltrate islets (insulitis)
4. Beta cells destroyed via: perforin/granzyme pathway, Fas-FasL apoptosis, cytokine release (TNF-α, IL-1β, IFN-γ)
5. Clinical disease appears only after ~80-90% loss

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Type 2 DM - Pancreatic Histopathology

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1.2 Vascular Pathology - The Basis of All Chronic Complications

Mechanism 1: Advanced Glycation End-Products (AGEs)

• Glucose non-enzymatically glycates proteins → AGEs
• AGEs cross-link collagen in vessel walls → increased stiffness, decreased elasticity
• AGEs bind RAGE receptors → NF-κB activation → inflammation, oxidative stress
• AGEs on GBM displace heparan sulfate → lose negative charge → proteinuria

Mechanism 2: Polyol Pathway (Aldose Reductase)

• Excess glucose → sorbitol (via aldose reductase) → fructose
• Sorbitol accumulates intracellularly (osmotic stress) → pericyte loss in retinal vessels
• Depletes NADPH → decreased glutathione → oxidative damage
• Important in retinopathy, neuropathy, cataracts

Mechanism 3: Protein Kinase C (PKC) Activation

• Diacylglycerol (DAG) accumulates with high glucose → activates PKC
• PKC activation → increased VEGF (neovascularization), increased permeability, decreased NO production, increased ET-1 (vasoconstriction)

Mechanism 4: Hexosamine Pathway

• Excess glucose enters hexosamine pathway → glucosamine → O-GlcNAc modification of proteins
• Alters gene expression → increased TGF-β, PAI-1 → fibrosis and thrombosis

Two types of vascular disease:

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1.3 Diabetic Nephropathy (Pathology in Detail)

Epidemiology of DN

• Single most common cause of chronic kidney disease and ESRD in the US and worldwide
• ~40% of all diabetics develop nephropathy
• Majority have T2DM (due to higher prevalence vs T1DM)

Histologic Stages

• Sensitive indicator for presence of diabetes
• GBM composition altered: loss of heparan sulfate → negative charge lost → protein filtration begins
• Correlates poorly with clinical nephropathy alone

• Accumulation of extracellular matrix in the mesangium
• Driven by TGF-β, CTGF, AGEs, glomerular hypertension
• Leads to mesangial sclerosis

• Diffuse increase in mesangial matrix throughout all glomeruli
• Most common histologic lesion; does not exclusively indicate DN

• Eosinophilic, PAS-positive nodular deposits in the mesangium
• Located at the periphery of the glomerular lobule
• Pathognomonic for diabetic nephropathy - but present in only ~25% of DN cases
• Strong correlation: presence of KW nodules ↔ presence of retinopathy (>90% in T1DM)
• Differential: amyloidosis, light-chain deposition disease (but DN nodes are PAS+, Congo red-)

• Hyaline arteriolosclerosis - afferent AND efferent arterioles (efferent > afferent involvement is specific for DM)
• Fibrin cap lesions, capsular drop lesions (less common but specific)

• Tubulointerstitial fibrosis and tubular atrophy
• Glomerular obsolescence
• Armanni-Ebstein lesion: glycogen accumulation in tubular epithelial cells (seen with uncontrolled hyperglycemia)

Immunofluorescence

• Non-specific linear IgG staining along GBM ("linear staining" - not immune complex)
• No immune deposits on electron microscopy (distinguishes from lupus nephritis)

Glomerular Hemodynamic Changes (Pathogenesis of Progression)

• Hyperglycemia activates RAAS → increased angiotensin II → efferent arteriolar vasoconstriction → increased intraglomerular pressure
• Hyperglycemia upregulates SGLT1 and SGLT2 in proximal tubule → decreased NaCl delivery to macula densa → decreased TGF signal → afferent arteriolar dilation → further glomerular hyperfiltration
• Glomerular hypertension → GBM injury, increased matrix production → sclerosis

Natural History of Diabetic Nephropathy

Onset of DM
    ↓ (1-2 years)
GBM thickening + glomerular hyperfiltration (↑ GFR)
    ↓ (5-10 years)
Microalbuminuria (30-300 mg/24h or UACR 30-300 mg/g)
    ↓ (5-10 more years)
Macroproteinuria (>300 mg/24h) + declining GFR
    ↓
Nephrotic-range proteinuria (up to 25 g/24h)
    ↓
ESRD (dialysis/transplant)

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1.4 Diabetic Retinopathy (Pathology)

Core Pathologic Process

• Loss of pericytes (polyol pathway) → microaneurysm formation (earliest lesion)
• Increased vascular permeability → hard exudates (lipid/protein deposits)
• Retinal ischemia → cotton-wool spots (nerve fiber layer infarcts)
• VEGF upregulation → neovascularization (pathologic new vessel formation)

Classification of Diabetic Retinopathy (Goldman-Cecil / Kanski)

• Diabetic retinopathy is largely asymptomatic even with severe PDR
• Visual loss occurs with: vitreous hemorrhage, traction retinal detachment, DME
• Diplopia: acute CN III or VI mononeuropathy (common in DM - ischemic, pupil-sparing for CN III)

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1.5 Diabetic Neuropathy (Pathology)

Pathologic Mechanisms

1. Polyol pathway: Sorbitol accumulation in Schwann cells → osmotic injury → segmental demyelination
2. AGEs on myelin proteins → structural damage
3. Microangiopathy of vasa nervorum: Ischemia of endoneurial blood vessels → axonal degeneration
4. Oxidative stress + inflammation → nerve fiber loss

Histologic Findings

• Segmental demyelination and axonal loss (both myelinated and unmyelinated fibers)
• Thickening of endoneurial vessel walls (microangiopathy of vasa nervorum)
• Intraepidermal nerve fiber density reduced (skin punch biopsy quantifies small fiber loss)
• In autonomic neuropathy: depletion of neurons in autonomic ganglia and denervation of target organs

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PART 2: MEDICINE (Clinical Medicine)

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2.1 Diagnosis of Diabetes Mellitus

ADA Diagnostic Criteria (any ONE criterion = diabetes, confirmed on repeat unless unequivocal symptoms)

• Symptoms of hyperglycemia: polyuria, polydipsia, unexplained weight loss
• In asymptomatic patients, a second confirmatory test is required (unless two different tests simultaneously above threshold)

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2.2 Clinical Evaluation at Diagnosis

History

• Classic triad: Polyuria, polydipsia, polyphagia (more prominent in T1DM)
• Blurred vision (osmotic lens changes - reversible)
• Fatigue, weakness
• Frequent infections (vaginitis, fungal skin, UTI, boils)
• Slow wound healing
• Family history, weight history, sleep history, CVD risk factors

Physical Examination Findings

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2.3 Laboratory Monitoring in Established DM

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2.4 Glycemic Targets (Individualized)

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2.5 Acute Complications - Clinical Management

Diabetic Ketoacidosis (DKA) - Primarily T1DM

• Plasma glucose >250 mg/dL
• Arterial pH <7.3 (or venous pH <7.35)
• Serum bicarbonate <18 mEq/L
• Anion gap >12 (elevated anion gap metabolic acidosis)
• Positive ketones (urine or serum beta-hydroxybutyrate)

• Infection (most common - ~40%)
• Insulin omission/insufficient insulin
• Infarction (MI, stroke)
• Inflammation (pancreatitis)
• Iatrogen (steroids, SGLT-2 inhibitors)
• Initial presentation of T1DM

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Hyperosmolar Hyperglycemic State (HHS) - Primarily T2DM (Elderly)

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Hypoglycemia

• Level 1: 54-70 mg/dL (alert and treat)
• Level 2: <54 mg/dL (significant)
• Level 3: Severe cognitive impairment requiring external assistance

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2.6 Chronic Complications - Clinical Medicine

Diabetic Nephropathy

• T1DM: screen 5 years after diagnosis, then annually
• T2DM: screen at diagnosis, then annually (may already have nephropathy at diagnosis)

• Microalbuminuria (30-300 mg/g UACR): early DN; reversible with intervention
• Macroalbuminuria (>300 mg/g): established DN; progresses over 5-10 years
• Declining eGFR: CKD stages 3-5 → ESRD

• BP <130/80 mmHg - ACEi or ARB as first-line (both reduce proteinuria and slow progression; do NOT combine ACEi + ARB together)
• SGLT-2 inhibitors (empagliflozin, dapagliflozin, canagliflozin): renoprotective independent of glucose lowering; reduce intraglomerular pressure; proven to reduce ESRD and CV events
• Finerenone (selective mineralocorticoid receptor antagonist): reduces albuminuria progression and CV outcomes in CKD + T2DM

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Diabetic Retinopathy

• T1DM: begin 5 years after diagnosis
• T2DM: begin at diagnosis (hyperglycemia pre-dates diagnosis by years)
• Frequency: annually if no retinopathy; every 6 months if NPDR; more frequently if progressing

• Mild/Moderate NPDR: optimize glycemic and BP control, annual monitoring
• Severe NPDR/PDR: panretinal photocoagulation (PRP) - laser ablates ischemic retina to reduce VEGF
• DME: Anti-VEGF injections (ranibizumab, bevacizumab, aflibercept) - superior to focal laser; focal/grid laser for non-central DME

• Retinopathy may paradoxically worsen initially when glycemic control is rapidly improved (rapid HbA1c reduction)
• Retinopathy correlates with nephropathy: >90% of T1DM with nephropathy also have retinopathy; absence of retinopathy in T1DM nephropathy = suspect another diagnosis

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Diabetic Neuropathy

• "Glove and stocking" distribution; starts in feet
• Symptoms: burning, aching, tingling, numbness, hyperesthesia at night
• Signs: reduced vibration (128Hz tuning fork), reduced proprioception, reduced ankle reflexes, reduced pinprick/temperature (small fiber), reduced light touch (Semmes-Weinstein monofilament)
• 10g Semmes-Weinstein monofilament at-risk sites = gold standard screening tool
• Risk of painless ulcers due to sensory loss + Charcot neuroarthropathy

• 1st line: Duloxetine (SNRI) or Pregabalin/Gabapentin (calcium channel modulators)
• 2nd line: Tricyclic antidepressants (amitriptyline - beware cardiac effects, anticholinergic)
• Topical: Capsaicin cream, lidocaine patch
• NOT opioids as first line

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Cardiovascular Disease

• Leading cause of death in DM
• 2-4x increased risk of MI, stroke vs non-diabetics
• Women lose natural cardioprotection; 6x higher CVD mortality than non-diabetic women
• Diabetic cardiomyopathy: structural/functional cardiac dysfunction independent of CAD or HTN
• GLP-1 receptor agonists (liraglutide, semaglutide, dulaglutide): proven CV mortality benefit in T2DM with ASCVD
• SGLT-2 inhibitors (empagliflozin, canagliflozin): reduced CV mortality and heart failure hospitalizations in landmark trials (EMPA-REG, CANVAS, DAPA-HF)

Diabetic Foot

• Triad: neuropathy + ischemia (PAD) + infection → ulceration → amputation
• DM = leading cause of non-traumatic lower limb amputations
• Annual foot exam: monofilament, pulses, inspection for callus/ulcers/deformities
• Charcot neuroarthropathy: Progressive destruction of foot/ankle bones and joints due to repeated unperceived trauma in neuropathic foot; hot, swollen, painless foot; X-ray: "bag of bones"

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PART 3: PHARMACOLOGY

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3.1 Insulin

Physiology Reminder

• Insulin released from beta cells in two phases: first-phase (rapid, minutes, suppresses hepatic glucose output) and second-phase (sustained, hours, promotes peripheral uptake)
• In T1DM: both phases absent
• In T2DM: first-phase lost early; second-phase impaired later

Insulin Preparations (Lippincott Pharmacology)

• Long-acting insulins (glargine, detemir, degludec): never mix with other insulins (alters pharmacodynamic profile)
• NPH can be mixed with regular insulin
• Insulin has NO oral route (degraded by GI proteases); routes: SubQ, IV (regular only), inhaled

• ADA target: HbA1c ≤7% (mean glucose ~154 mg/dL)
• Intensive therapy (≥3 injections/day + frequent SMBG/CGM) significantly reduces microvascular complications vs standard therapy
• Caution: intensive therapy NOT recommended in long-standing DM with significant microvascular complications, advanced age, or hypoglycemia unawareness (increased seizures/coma risk)

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3.2 Oral and Injectable Antidiabetic Agents

A. Biguanides - Metformin ⭐ (First-line T2DM)

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B. Sulfonylureas (Insulin Secretagogues)

• Potentiate hypoglycemia: NSAIDs, warfarin, fibrates (gemfibrozil), fluconazole, MAOIs
• Reduce efficacy: rifampin, thiazides, corticosteroids, oral contraceptives

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C. Meglitinides (Short-acting Insulin Secretagogues)

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D. Thiazolidinediones / TZDs (Insulin Sensitizers)

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E. DPP-4 Inhibitors ("Gliptins")

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F. GLP-1 Receptor Agonists ("Incretin Mimetics")

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G. SGLT-2 Inhibitors ("Gliflozins")

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H. Alpha-Glucosidase Inhibitors

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3.3 Pharmacology Summary Table

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3.4 Stepped Management Algorithm (T2DM - ADA 2024 Framework)

Step 1: LIFESTYLE modification (diet, exercise, weight loss)
    + METFORMIN at diagnosis (unless contraindicated)
         ↓
Step 2: If HbA1c not at target after 3 months:
    Add agent based on PRIORITY DRIVER:
    ┌─ ASCVD present → GLP-1 RA or SGLT-2i (proven CV benefit)
    ├─ Heart failure or CKD → SGLT-2i first
    ├─ Weight loss needed → GLP-1 RA (or tirzepatide)
    ├─ Hypoglycemia avoidance → DPP-4i, GLP-1 RA, SGLT-2i
    └─ Cost priority → Sulfonylurea or TZD
         ↓
Step 3: If still not at target:
    Combine 2-3 agents from different classes
         ↓
Step 4: Consider insulin if:
    - HbA1c very high (>10%) at diagnosis (start immediately)
    - Progressive beta-cell failure despite combination therapy
    - Catabolic features (weight loss, DKA risk)
         ↓
Step 5: Insulin intensification
    Basal insulin → Basal + prandial (basal-bolus regimen)

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• Harrison's Principles of Internal Medicine, 22nd Edition (2025) - Chapters 415-417, 326
• Lippincott Illustrated Reviews: Pharmacology - Chapter 24
• Goldman-Cecil Medicine, International Edition - Chapter 210 (Diabetic Retinopathy classification)
• Comprehensive Clinical Nephrology, 7th Edition - Chapter 31 (Diabetic Nephropathy)
• Kanski's Clinical Ophthalmology, 10th Edition - Chapter on Diabetic RetinopathyHere's a breakdown of what's in each section:

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What Was Added

PART 1 - PATHOLOGY

• Pancreatic histopathology for both T1DM and T2DM side-by-side - insulitis, IAPP amyloid, beta-cell mass changes
• 4 molecular mechanisms of vascular damage: AGEs, polyol pathway (aldose reductase), PKC activation, hexosamine pathway - these are the "why" behind every complication
• Diabetic nephropathy in depth: GBM changes, Kimmelstiel-Wilson nodules (PAS+, pathognomonic), diffuse vs nodular glomerulosclerosis, immunofluorescence findings, the SGLT/RAAS glomerular hemodynamic model, and the full natural history timeline
• Diabetic retinopathy staging: the full 5-stage classification table (mild NPDR → PDR) with the "4-2-1 rule" for severe NPDR
• Diabetic neuropathy histology: segmental demyelination, axonal loss, vasa nervorum microangiopathy

PART 2 - MEDICINE

• ADA diagnostic criteria table with pre-diabetes thresholds
• Full clinical evaluation (history + physical exam findings including acanthosis nigricans, necrobiosis lipoidica)
• Monitoring schedule with targets (HbA1c, UACR, eGFR, lipids, foot exam)
• DKA management - the 4 pillars, resolution criteria, why K⁺ must be replicated before insulin
• HHS vs DKA comparison
• Hypoglycemia classification and the cardiovascular danger of hypoglycemia
• Chronic complication management: nephropathy (ACEi/ARB, SGLT-2i, finerenone), retinopathy (PRP laser vs anti-VEGF), painful neuropathy drugs, autonomic neuropathy by system, CV benefit drugs, Charcot foot

PART 3 - PHARMACOLOGY

• Every drug class: mechanism, HbA1c reduction, weight effect, hypoglycemia risk, adverse effects, contraindications
• Insulin preparation table with onset/peak/duration for each type and clinical rationale
• Euglycemic DKA from SGLT-2 inhibitors explained (easily missed!)
• Landmark trials referenced (EMPA-REG, CREDENCE, LEADER, UKPDS, DCCT)
• ADA 2024 stepped management algorithm with priority-driver decision tree