DIabetes for 2nd BDS students pathology every thing about it

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Diabetes Mellitus - Complete Pathology Notes for 2nd BDS

Source: Robbins & Kumar Basic Pathology + Robbins & Cotran Pathologic Basis of Disease

1. DEFINITION

Diabetes mellitus (DM) is a group of metabolic disorders characterized by hyperglycemia, resulting from defects in insulin secretion, insulin action, or most commonly, both. Chronic hyperglycemia causes damage to the kidneys, eyes, nerves, and blood vessels.

2. EPIDEMIOLOGY

Over 37 million Americans (11% of population) have diabetes
~1.4 million new cases diagnosed per year in the USA
Leading cause of: end-stage renal disease, adult-onset blindness, nontraumatic lower-limb amputations

3. CLASSIFICATION

Type	Old Name	Key Feature
Type 1 DM (T1D)	Juvenile-onset / Insulin-dependent	Absolute insulin deficiency (autoimmune destruction of β-cells)
Type 2 DM (T2D)	Adult-onset / Non-insulin-dependent	Insulin resistance + relative insulin deficiency
Gestational DM	-	Onset during pregnancy
Monogenic / Secondary DM	MODY, etc.	Genetic defects, pancreatitis, drugs

4. DIAGNOSIS (ADA / WHO Criteria)

Test	Diabetes	Prediabetes
Fasting plasma glucose	≥126 mg/dL	100-125 mg/dL
Random plasma glucose	≥200 mg/dL (with symptoms)	-
2-hr OGTT	≥200 mg/dL	140-199 mg/dL
HbA1c	≥6.5%	5.7-6.4%

Note: All tests (except symptomatic random glucose) must be confirmed on a separate day.

5. TYPE 1 DIABETES (T1D)

Pathogenesis

T1D is an autoimmune disease resulting in the destruction of pancreatic β-cells. Key steps:

Genetic predisposition: ~90% of T1D patients carry HLA-DR3 and/or HLA-DR4 alleles. Polymorphisms in the insulin gene promoter also predispose.
Environmental triggers: Viral infections (Coxsackievirus B, CMV) may initiate autoimmunity by:
- Directly infecting and destroying β-cells
- Inducing an immune response that cross-reacts with β-cell antigens (molecular mimicry)
Autoimmune destruction: CD4+ and CD8+ T lymphocytes infiltrate the islets (insulitis). Autoantibodies to:
- Glutamic acid decarboxylase (GAD)
- Insulin
- Islet cell antigens (IA-2)
Progressive loss of β-cells → absolute insulin deficiency

Morphology (Microscopic)

Insulitis: Lymphocytic infiltration of the islets of Langerhans
Reduction in islet size and number
Selective loss of β-cells (α-cells remain intact)
In end-stage disease: islets appear fibrosed and atrophic

6. TYPE 2 DIABETES (T2D)

Pathogenesis - Two Key Defects

A. Peripheral Insulin Resistance

Cells (especially muscle, liver, adipose tissue) fail to respond to insulin
Obesity (especially abdominal/visceral fat) is the major risk factor
Adipokines (from fat cells) and free fatty acids impair insulin signaling
Insulin receptors and post-receptor signaling are defective

B. β-Cell Dysfunction (Relative Insulin Deficiency)

Initially: β-cells compensate by secreting more insulin (hyperinsulinemia)
Over time: β-cells become exhausted; insulin secretion declines
Amyloid deposition in islets further impairs function

Role of Obesity

Obesity (especially central/visceral fat) leads to:

Elevated free fatty acids → lipotoxicity of β-cells
Adipokines (leptin, adiponectin resistance, resistin) promoting insulin resistance
Chronic low-grade inflammation (TNF-α, IL-6 from adipose tissue)

Morphology (Microscopic)

Amyloid (islet amyloid polypeptide / amylin) deposits in the islets - most characteristic finding
Reduction in number and size of islets (less dramatic than T1D)
No insulitis (no lymphocytic infiltration)
β-cell mass is reduced (by ~20-65%)

7. NORMAL INSULIN PHYSIOLOGY (Review)

Produced by β-cells of the islets of Langerhans (pancreas)
Stimulated by: glucose, amino acids, GLP-1, GIP
Key effects:
- Liver: Promotes glycogen synthesis; inhibits gluconeogenesis
- Muscle: Promotes glucose uptake (via GLUT-4) and glycogen synthesis
- Adipose: Promotes lipogenesis; inhibits lipolysis
- All tissues: Promotes protein synthesis

8. MORPHOLOGY OF DIABETES (Summary Table)

Organ/Tissue	Findings
Pancreas - T1D	Insulitis; reduced islets; β-cell loss; leukocyte infiltration
Pancreas - T2D	Islet amyloid deposits (amylin); slight reduction in β-cells
Blood vessels (macro)	Accelerated atherosclerosis
Small vessels (micro)	Microangiopathy - basement membrane thickening
Kidney	Diffuse/nodular glomerulosclerosis (Kimmelstiel-Wilson lesion); tubular glycogen (Armanni-Ebstein lesion); arteriolar hyalinosis
Eye	Retinal microaneurysms, neovascularization, exudates; cataracts; glaucoma
Nerves	Segmental demyelination; Schwann cell injury
Skin	Carbuncles, necrobiosis lipoidica diabeticorum

9. LONG-TERM (CHRONIC) COMPLICATIONS

The diagram below shows the systemic complications of diabetes:

Long-term complications of diabetes - Robbins Basic Pathology

A. Diabetic Macrovascular Disease

Mechanism: Accelerated atherosclerosis
Consequences:
- Myocardial infarction (most common cause of death)
- Stroke / cerebral vascular infarcts
- Peripheral vascular disease → gangrene of lower limbs

B. Diabetic Microangiopathy

Mechanism: Basement membrane thickening of capillaries and small vessels
Caused by AGEs, PKC activation, polyol pathway disturbances

Retinopathy:

Microaneurysms (earliest lesion), dot-blot hemorrhages
Hard exudates (lipid deposits)
Cotton-wool spots (soft exudates = microinfarcts)
Neovascularization (proliferative retinopathy)
Leading cause of adult-onset blindness

Nephropathy:

Diffuse glomerulosclerosis: Diffuse increase in mesangial matrix and BM thickening (most common)
Nodular glomerulosclerosis (Kimmelstiel-Wilson lesion): Pathognomonic - ovoid/spherical deposits of laminated matrix in mesangium
Afferent AND efferent arteriolar hyalinosis (efferent hyalinosis is virtually diagnostic of diabetes)
Armanni-Ebstein lesion: glycogen accumulation in tubular epithelial cells
Increased susceptibility to pyelonephritis and necrotizing papillitis

Neuropathy:

Peripheral neuropathy: segmental demyelination, axonal damage
Autonomic neuropathy: impaired sweating, postural hypotension, bladder dysfunction, impotence, GI dysmotility

C. Mechanisms of Chronic Complications (4 Main Pathways)

1. Advanced Glycation End Products (AGEs)

Formed by non-enzymatic glycation of proteins
AGEs bind RAGE receptors → release TGF-β (fibrosis), VEGF (neovascularization), ROS
Cross-link extracellular matrix → trap LDL → accelerate atherosclerosis
Trap albumin in capillary walls → basement membrane thickening

2. Protein Kinase C (PKC) Activation

Intracellular hyperglycemia → ↑DAG → activates PKC
Downstream: ↑VEGF (retinopathy), ↑TGF-β (fibrosis, basement membrane deposition)

3. Polyol Pathway

In insulin-independent tissues (lens, nerves, kidney): excess glucose → sorbitol (via aldose reductase)
Sorbitol accumulates → osmotic damage, ↓myoinositol, ↓Na+/K+ ATPase activity → nerve dysfunction (neuropathy), cataract

4. Hexosamine Pathway

Excess glucose → glucosamine-6-phosphate → modifies transcription factors
Leads to abnormal gene expression and cellular dysfunction

10. ACUTE COMPLICATIONS

Complication	Type	Features
Diabetic Ketoacidosis (DKA)	T1D mainly	Absolute insulin deficiency → unregulated lipolysis → fatty acids → ketones (β-hydroxybutyrate, acetoacetate) → metabolic acidosis, Kussmaul breathing, fruity breath
Hyperosmolar Hyperglycemic State (HHS)	T2D mainly	Extreme hyperglycemia (>600 mg/dL), severe dehydration, no significant ketoacidosis (residual insulin prevents lipolysis)
Hypoglycemia	Both types	Excess insulin/oral agents; can cause loss of consciousness

DKA Mechanism:

No insulin → ↑glucagon → ↑gluconeogenesis, ↑glycogenolysis
↑lipolysis → ↑free fatty acids → ↑ketogenesis in liver
Ketones = organic acids → metabolic acidosis
Osmotic diuresis → dehydration, electrolyte loss

11. CLINICAL FEATURES

Classic Triad ("3 Polys")

Polyuria - osmotic diuresis from glycosuria (glucose exceeds renal threshold ~180 mg/dL)
Polydipsia - secondary to water loss
Polyphagia - cellular starvation despite hyperglycemia (cells cannot uptake glucose)

Other Features

Weight loss (especially T1D - catabolism)
Fatigue, blurred vision
Recurrent infections (impaired leukocyte function, high glucose supports microbial growth)

HbA1c (Glycated Hemoglobin)

Reflects average blood glucose over past 2-3 months (lifespan of RBC)
Formed by non-enzymatic glycation of Hb-A by glucose
Target in diabetic management: <7%
Diagnostic of DM: ≥6.5%

12. GESTATIONAL DIABETES MELLITUS (GDM)

Glucose intolerance first recognized during pregnancy
Due to placental hormones (hPL, progesterone, cortisol) causing insulin resistance
Risk: macrosomia, neonatal hypoglycemia, increased risk of T2D later in both mother and child
Screening: 24-28 weeks gestation with 50g GCT, confirmed with 75g OGTT

13. MONOGENIC / SECONDARY DIABETES

MODY (Maturity-Onset Diabetes of the Young)

Autosomal dominant mutations in single genes affecting β-cell function
MODY 2: Glucokinase gene mutation (glucose sensor defect)
MODY 3: HNF-1α mutation (most common MODY)

Secondary Causes:

Pancreatitis / pancreatectomy
Hemochromatosis (iron deposits destroy islets - "bronze diabetes")
Cushing's syndrome (↑cortisol → insulin resistance)
Acromegaly (↑GH → insulin resistance)
Drug-induced (glucocorticoids, thiazide diuretics, protease inhibitors)

14. ORAL / DENTAL RELEVANCE FOR BDS STUDENTS

Diabetes has important implications for dental practice:

Oral Feature	Mechanism
Periodontal disease (most common oral complication)	Microangiopathy of periodontal vessels + impaired leukocyte function + altered collagen metabolism → severe, rapidly progressing periodontitis
Xerostomia (dry mouth)	Autonomic neuropathy of salivary glands; dehydration
Increased caries	Reduced salivary flow; high glucose in saliva
Oral candidiasis	Immunosuppression + high salivary glucose
Poor wound healing	Microangiopathy + impaired neutrophil function + neuropathy
Burning mouth syndrome	Peripheral neuropathy
Tooth mobility	Alveolar bone loss from severe periodontitis
Acetone breath	DKA - recognizable in dental chair as fruity/acetone odor

Key dental management point: Never perform elective dental procedures if blood glucose is >200 mg/dL. Risk of hypoglycemia during dental visits (stress-induced, missed meals). Always have glucose source available.

15. COMPARISON: T1D vs T2D

Feature	Type 1 DM	Type 2 DM
Age of onset	Usually <30 yrs (juvenile)	Usually >40 yrs (but rising in youth)
Body habitus	Normal / thin	Obese (80%)
Onset	Abrupt	Insidious
Insulin levels	Very low / absent	Normal or elevated initially
C-peptide	Absent	Present
Autoantibodies	Present (anti-GAD, anti-insulin)	Absent
HLA association	HLA-DR3, DR4	Weak HLA association
Pathology	Insulitis, β-cell destruction	Islet amyloid, insulin resistance
Ketoacidosis	Common	Rare
Treatment	Insulin mandatory	Diet, exercise, oral agents, ± insulin

16. QUICK EXAM BUZZWORDS

Kimmelstiel-Wilson nodules = nodular glomerulosclerosis in T2D (pathognomonic)
Insulitis = lymphocytic infiltration of islets = T1D
Islet amyloid (amylin/IAPP deposits) = T2D
Armanni-Ebstein lesion = glycogen in tubular cells = uncontrolled DM
RAGE = receptor for AGEs
Efferent arteriolar hyalinosis = virtually diagnostic of DM (different from hypertension which only affects afferent)
HbA1c ≥6.5% = diagnostic
MODY = Maturity Onset Diabetes of the Young
DKA = T1D; HHS = T2D
Sorbitol = polyol pathway → cataract + neuropathy

Sources: Robbins & Kumar Basic Pathology (9780323790185), Robbins & Cotran Pathologic Basis of Disease (9780443264528)

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