A 58-year-old man from rural India presents with progressive renal insufficiency. He has a 15-year history of poorly controlled hypertension and type 2 diabetes mellitus. Serum creatinine is 3.2 mg/dL, and urinalysis shows 3+ proteinuria with no active urinary sediment. What is the most common histopathological finding in his kidneys?

## Histopathology of Diabetic Nephropathy **Key Point:** Nodular glomerulosclerosis (Kimmelstiel-Wilson lesion) is the pathognomonic and most common histological finding in diabetic nephropathy, seen in 25–50% of patients with long-standing diabetes and proteinuria. ### Clinical Context This patient has: - Long-standing type 2 diabetes (15 years) - Poorly controlled hypertension - Significant proteinuria (3+) - Preserved urinary sediment (no RBC casts or dysmorphic RBCs) - Elevated creatinine indicating advanced CKD The absence of active urinary sediment rules out crescentic or rapidly progressive glomerulonephritis, pointing toward a chronic, non-inflammatory process — diabetic nephropathy. ### Stages of Diabetic Nephropathy (Pathological) | Stage | Histology | Clinical Features | |-------|-----------|-------------------| | I | Glomerular basement membrane thickening | Hyperfiltration; normal GFR | | II | Nodular glomerulosclerosis (early) | Microalbuminuria; GFR ↑ | | III | Nodular glomerulosclerosis (advanced) | Overt proteinuria; GFR declining | | IV | Global glomerulosclerosis + tubular atrophy | Heavy proteinuria; CKD Stage 4–5 | | V | Complete glomerular sclerosis | ESRD | **High-Yield:** Kimmelstiel-Wilson nodules are **PAS-positive, diastase-resistant** hyaline deposits in the glomerular mesangium, visible on light microscopy and electron microscopy. ### Microscopic Features of Diabetic Nephropathy 1. **Light Microscopy:** - Nodular mesangial expansion (Kimmelstiel-Wilson lesion) - Diffuse mesangial thickening - Basement membrane thickening (30–40 nm; normal ~350 nm) - Hyaline arteriolosclerosis in afferent and efferent arterioles 2. **Electron Microscopy:** - Thickened glomerular basement membrane (GBM) - Mesangial expansion with electron-dense material - Effacement of podocyte foot processes **Clinical Pearl:** Diabetic nephropathy is the only major kidney disease where **nodular glomerulosclerosis** is the hallmark finding. Its presence on biopsy confirms diabetic kidney disease.