Diabetic Nephropathy (Diabetic Kidney Disease)

Definition and Epidemiology

• Harrison's Principles of Internal Medicine, 22E, p. 3267-3268
• Brenner and Rector's The Kidney, p. 3381

Pathogenesis

• Harrison's, p. 3268
• Brenner and Rector's The Kidney, p. 3381

Pathology

1. Glomerular Lesions (most important)

• Detectable by electron microscopy within a few years of DM onset, often before any functional change
• Thickening occurs along the entire capillary length

• Increase in mesangial matrix + mesangial cell proliferation + BM thickening
• Present in most patients with >10 years of disease

• Ball-like laminated matrix deposits in the glomerular periphery
• Seen in ~15-30% of long-term diabetics
• Virtually pathognomonic of diabetes (distinguishes it from diffuse form)
• Major contributor to renal dysfunction; when severe, causes nephrotic syndrome

Nodular glomerulosclerosis (Kimmelstiel-Wilson lesion), PAS stain - Robbins Basic Pathology

2. Vascular Lesions

• Hyaline arteriolosclerosis affects both afferent AND efferent arterioles - efferent involvement is virtually unique to diabetes
• Renal atherosclerosis as part of systemic macrovascular disease
• Vascular compromise → ischemia → diffuse cortical scarring (nephrosclerosis) → finely granular cortical surface

3. Tubular and Interstitial Lesions

• Thickening of tubular basement membranes
• Pyelonephritis (both acute and chronic) - more severe in diabetics
• Necrotizing papillitis (papillary necrosis) - much more prevalent in diabetics
• Robbins & Kumar Basic Pathology, p. 751

Natural History / Stages

Natural history of diabetic nephropathy - Harrison's 22E, Fig. 417-3

• Once marked albuminuria and GFR reduction occur, pathologic changes are likely irreversible
• Harrison's, p. 3268

Screening and Diagnosis

• Screen with both UACR (spot urine) and eGFR - some patients have GFR decline without albuminuria
• Type 1 DM: Screen 5 years after diagnosis, then annually
• Type 2 DM: Screen at time of diagnosis, then annually
• ADA defines albuminuria as UACR >30 mg/g (persistently elevated on 2-3 occasions over 3-6 months)
  • Moderate: 30-299 mg/g creatinine
  • Severely elevated: ≥300 mg/g creatinine
• Confirm elevated UACR on 2-3 occasions (rule out: exercise, fever, UTI, CHF, hyperglycemia, hypertension)
• Routine urinalysis does not detect low-level albuminuria

Concurrent findings to monitor:

• Type IV RTA (hyporeninemic hypoaldosteronism) → hyperkalemia + acidemia - exacerbated by ACEi/ARBs/MRAs
• Radiocontrast nephrotoxicity risk is elevated; ensure adequate hydration pre/post procedure
• Harrison's, p. 3268-3269

Treatment

1. Glycemic Control

• Reduces rate of albuminuria onset and progression in both T1D and T2D
• Less effective once moderate albuminuria is established
• Glucose-lowering adjustments by eGFR:
  • Sulfonylureas and metformin: contraindicated in advanced CKD
  • SGLT2 inhibitors: not effective with eGFR <20 mL/min/1.73 m²
  • GLP-1 agonists and DPP-4 inhibitors: may require dose adjustment
• 10 years of normoglycemia (via pancreas transplantation) can reverse mesangial lesions

2. Blood Pressure Control

• Target: <130/80 mmHg (possibly lower if high ASCVD or CKD progression risk)
• If BP >150/90 mmHg: start with two antihypertensive agents
• Lifestyle: weight loss, sodium restriction, DASH-style diet, exercise, smoking cessation

3. RAAS Blockade (cornerstone)

• ACEi or ARB: first-line for any patient with DM + albuminuria or CKD
  • Reduces albuminuria and slows GFR decline in T1D and T2D
  • Both classes considered equivalent
  • Use ARB as alternative if ACEi causes cough/angioedema
  • Titrate to maximum tolerated dose
  • A rise in serum creatinine up to 30% is acceptable
  • Dose goal in overt proteinuria (UACR >300 mg/g): reduce UACR by ≥30%
  • Monitor serum K⁺ closely
  • Do not combine ACEi + ARB (no added benefit, increased harm)

4. SGLT-2 Inhibitors (transformative modern addition)

• Recommended with eGFR >20 mL/min/1.73 m² in type 2 DM + CKD (with any level of albuminuria), added to ACEi/ARB
• Reduce CKD progression and cardiovascular events
• Mechanism: reduce intraglomerular pressure, reduce glucotoxicity, reduce tubular workload
• Caution in T1DM/insulin-deficient T2DM: risk of euglycemic DKA

5. Finerenone (Nonsteroidal MRA)

• Reduces cardiovascular risk in type 2 DM + CKD
• More selective and less hyperkalemia risk than spironolactone/eplerenone
• Monitor K⁺ closely; avoid dual MRA + high-dose RAASi

6. GLP-1 Receptor Agonists

• Semaglutide specifically improves kidney outcomes and reduces cardiovascular death in type 2 DM + CKD
• Also reduces body weight and blood pressure

7. Lipid Management

• ASCVD is the leading cause of death in patients with DN - treat dyslipidemia aggressively (statins)

8. Dietary Protein Restriction

• ADA recommends: 0.8 g/kg/day protein in patients with diabetic kidney disease

9. Nephrology Referral Indications

• eGFR <30 mL/min/1.73 m²
• Albuminuria >300 mg/g creatinine
• Atypical features: hematuria, rapidly declining renal function

10. Renal Replacement Therapy

• Preemptive (pre-dialysis) kidney transplantation from living donor should be considered approaching ESKD
• For T1DM or insulin-deficient T2DM: simultaneous pancreas-kidney (SPK) transplant from deceased donor is an option
• SPK prevents recurrence of diabetic nephropathy in the allograft
• Hemodialysis in DM: more complications (hypotension from autonomic neuropathy, difficult vascular access, accelerated ASCVD)
• Harrison's 22E, p. 3268-3270

Summary Table: Key Drug Therapies

Recent Evidence Update

• Harrison's Principles of Internal Medicine, 22E (2025) - Chap. 417
• Robbins & Kumar Basic Pathology - Chap. 18
• Brenner and Rector's The Kidney - Chap. 80 and 6
• Goldman-Cecil Medicine - Chap. 109

Symptoms of Diabetic Nephropathy

Stage-by-Stage Symptoms

Stage I - Hyperfiltration (onset)

• No symptoms
• GFR elevated (>150 mL/min), kidneys enlarge
• Blood pressure: normal (in T1DM); may already be elevated in 10-25% of T2DM patients
• Transient microalbuminuria may appear under stress (exercise, illness, poor glycemic control) but disappears at rest
• Kidney enlargement detectable on imaging but not clinically apparent

Stage II - Silent/Structural (years 0-5)

• Completely asymptomatic
• GFR ~150 mL/min (still elevated or normalizing)
• Normal albumin excretion (<30 mg/day) on standard testing
• Structural damage (GBM thickening, mesangial expansion) is already occurring at the microscopic level
• Blood pressure: normal

Stage III - Incipient Nephropathy / Microalbuminuria (~5-10 years)

• Still largely asymptomatic - detected only by laboratory screening
• Fixed microalbuminuria (30-300 mg/day; UACR 30-299 mg/g)
• GFR ~125 mL/min (still relatively preserved)
• Blood pressure begins to rise - often the first detectable clinical sign in T1DM
• In T2DM, pre-existing hypertension becomes harder to control
• Commonly associated with other microvascular signs: proliferative retinopathy, peripheral neuropathy - their co-presence supports the diagnosis
• Microalbuminuria is a risk marker for cardiovascular disease even at this stage

Stage IV - Overt Nephropathy (~10-15 years)

• A subset of T2DM patients develops progressive CKD without nephrotic-range proteinuria - an atypical presentation

Stage V - Uremia / ESKD (>15-20 years)

Associated / Concurrent Symptoms (all stages)

• Diabetic retinopathy - visual blurring, floaters, reduced vision (virtually always present with overt nephropathy; its absence should prompt reconsideration of the diagnosis)
• Peripheral neuropathy - numbness, tingling, burning pain in feet ("glove-and-stocking" distribution)
• Autonomic neuropathy - postural hypotension, gastroparesis (bloating, nausea), erectile dysfunction, neurogenic bladder
• Recurrent UTIs / pyelonephritis - flank pain, dysuria, fever (diabetics are more susceptible, and papillary necrosis can occur - presenting as hematuria + colicky pain)
• Hyperkalemia - muscle weakness, palpitations (from Type IV RTA / hyporeninemic hypoaldosteronism, worsened by ACEi/ARBs)

Key Clinical Rule

Diabetic nephropathy = "a disease found on a test, not from a complaint."