diabetic glomerulosclerosis

**Pathophysiology** - Chronic hyperglycemia causes non-enzymatic glycation of proteins, forming advanced glycation end products (AGEs). It also activates the polyol pathway, PKC, and TGF-β. - Glycation of the GBM and mesangial matrix leads to GBM thickening and mesangial expansion with increased matrix deposition. - Nonenzymatic glycosylation of the efferent arteriole (more than the afferent) raises intraglomerular pressure. This causes early hyperfiltration (increased GFR), then hyaline arteriolosclerosis and progressive loss of GFR. - Loss of GBM charge selectivity (loss of heparan sulfate) and podocyte injury cause albuminuria.

**Histology** - Early: GBM thickening, mesangial expansion (visible on EM). - Diffuse mesangial sclerosis. - Nodular glomerulosclerosis (Kimmelstiel-Wilson lesions): eosinophilic, PAS-positive nodules in the mesangium. This is pathognomonic, though not the most common pattern. - Hyaline arteriolosclerosis of both afferent and efferent arterioles. This is more severe than in hypertension, where mainly the afferent is affected. - Other findings: capsular drop lesions, fibrin caps.

**Clinical course** 1. Hyperfiltration and renal hypertrophy (high GFR). 2. Silent phase with GBM thickening. 3. Microalbuminuria (30–300 mg/day or ACR 30–300 mg/g), the earliest clinical sign. Screen at diagnosis in T2DM and 5 years after diagnosis in T1DM, then annually. 4. Overt proteinuria and nephrotic syndrome (proteinuria, hypoalbuminemia, edema, hyperlipidemia), with HTN. 5. Progressive CKD leading to ESRD (typically 10–20+ years after onset of T1DM). - Diabetic retinopathy usually coexists. Absence of retinopathy in T1DM should prompt a search for another cause of renal disease.

**Management** - Tight glycemic control (HbA1c goal ~<7%) and BP control (<130/80). - ACE inhibitors or ARBs are first-line for renoprotection. They dilate the efferent arteriole and lower intraglomerular pressure. Monitor K⁺ and creatinine. - SGLT2 inhibitors (e.g., empagliflozin, dapagliflozin) slow CKD progression and reduce CV risk. They work partly by restoring tubuloglomerular feedback and constricting the afferent arteriole. - Finerenone (nonsteroidal MR antagonist) and GLP-1 agonists show additional renal and CV benefit. - Statins, a low-protein/low-salt diet, and avoiding nephrotoxins (NSAIDs, contrast). - Dialysis or transplant for ESRD.

**High-yield associations** - Leading cause of ESRD in the US. - Nephrotic syndrome in adults: diabetic nephropathy is the most common cause overall, and FSGS is the most common primary cause. - Differential for nodular glomerulosclerosis: amyloidosis (Congo red, apple-green birefringence), light chain deposition disease, MPGN, and idiopathic nodular glomerulosclerosis (smokers, HTN). - Type IV RTA (hyporeninemic hypoaldosteronism) is a common associated finding, causing hyperkalemia. - Can cause hyperkalemia with ACE inhibitors and reduced insulin clearance, so hypoglycemia risk rises as GFR falls. - Urinalysis: protein; fatty (oval fat body) casts in nephrotic range.