Internal Medicine Exam Nephrology and Kidney Injury 2 — Questions and Answers
Question 1: A 58-year-old man with CKD stage 3b has a serum potassium of 6.2 mEq/L and ECG changes including peaked T-waves. Which intervention should be given FIRST?
- Sodium polystyrene sulfonate
- IV calcium gluconate (Correct answer)
- Sodium bicarbonate
- Furosemide
Correct answer: IV calcium gluconate
IV calcium gluconate stabilizes the cardiac membrane and is the first-line treatment for hyperkalemia with ECG changes.
Question 2: A patient on long-term lithium therapy presents with polyuria (5 L/day) and dilute urine despite water deprivation. Urine osmolality fails to rise with exogenous ADH. What is the diagnosis?
- Central diabetes insipidus
- Nephrogenic diabetes insipidus (Correct answer)
- Primary polydipsia
- SIADH
Correct answer: Nephrogenic diabetes insipidus
Lithium causes nephrogenic diabetes insipidus by blocking ADH action on collecting duct V2 receptors, so exogenous ADH has no effect.
Question 3: A 72-year-old woman receives IV contrast for a CT scan. Her baseline creatinine is 1.8 mg/dL. Creatinine rises to 2.6 mg/dL at 48 hours. Which finding best distinguishes contrast-induced nephropathy from pre-renal azotemia?
- Urine sodium > 40 mEq/L (Correct answer)
- BUN:creatinine ratio > 20
- Rapid recovery within 24 hours
- Response to IV fluids
Correct answer: Urine sodium > 40 mEq/L
A urine sodium >40 mEq/L indicates tubular dysfunction (FENa >1%), consistent with intrinsic AKI such as contrast nephropathy rather than pre-renal azotemia.
Question 4: A 35-year-old woman with SLE develops new proteinuria (3.5 g/day) and hematuria. Renal biopsy shows diffuse proliferative glomerulonephritis with subendothelial deposits. Which WHO/ISN class is this?
- Class II (mesangial)
- Class III (focal proliferative)
- Class IV (diffuse proliferative) (Correct answer)
- Class V (membranous)
Correct answer: Class IV (diffuse proliferative)
Diffuse proliferative lupus nephritis with subendothelial deposits involving >50% of glomeruli is classified as ISN/RPS Class IV and carries the worst prognosis.
Question 5: A 45-year-old man with hypertension takes an ACE inhibitor. His serum creatinine rises from 1.0 to 2.1 mg/dL within one week of starting the drug. Renal artery duplex shows high-grade bilateral stenosis. What is the mechanism of AKI?
- Direct tubular toxicity of ACE inhibitor
- Loss of efferent arteriolar tone reducing GFR (Correct answer)
- Immune-mediated glomerulonephritis
- Contrast nephropathy from the duplex study
Correct answer: Loss of efferent arteriolar tone reducing GFR
ACE inhibitors block angiotensin II-mediated efferent arteriolar constriction; in bilateral renal artery stenosis this drops glomerular filtration pressure critically.
Question 6: A 62-year-old man with myeloma presents with AKI, hypercalcemia, and anemia. Urinalysis shows no blood or protein by dipstick but urine protein electrophoresis reveals a spike. Which cast type is pathognomonic on renal biopsy?
- Granular casts
- Waxy broad casts
- Myeloma (Bence Jones) casts (Correct answer)
- Red blood cell casts
Correct answer: Myeloma (Bence Jones) casts
Myeloma kidney shows large, fractured eosinophilic casts composed of light chains (Bence Jones protein) surrounded by giant cells in tubular lumina.
Question 7: A 28-year-old man presents with hematuria and deafness since childhood. Electron microscopy of his renal biopsy shows thinning and splitting of the glomerular basement membrane in a 'basket-weave' pattern. What is the inheritance pattern of this condition?
- Autosomal dominant
- Autosomal recessive
- X-linked (most common form) (Correct answer)
- Mitochondrial
Correct answer: X-linked (most common form)
Alport syndrome most commonly results from X-linked mutations in COL4A5 encoding type IV collagen, causing nephritis, sensorineural deafness, and ocular abnormalities.
Internal Medicine Exam Nephrology and Kidney Injury 2
A 58-year-old man with CKD stage 3b has a serum potassium of 6.2 mEq/L and ECG changes including peaked T-waves.
Which intervention should be given FIRST?