Internal Medicine Exam Nephrology and Kidney Injury 4 — Questions and Answers
Question 1: A 60-year-old man with gout and CKD has a serum uric acid of 11 mg/dL. He starts allopurinol and develops a severe desquamating rash with hepatitis. Which HLA allele is strongly associated with allopurinol hypersensitivity syndrome?
- HLA-B*57:01
- HLA-B*58:01 (Correct answer)
- HLA-B*15:02
- HLA-A*31:01
Correct answer: HLA-B*58:01
HLA-B*58:01 is strongly associated with allopurinol-induced severe cutaneous adverse reactions, particularly in patients of Asian descent.
Question 2: A 45-year-old HIV-positive man on tenofovir develops proximal tubular dysfunction with glucosuria (normal serum glucose), phosphaturia, and aminoaciduria. What syndrome does this represent?
- Distal renal tubular acidosis
- Fanconi syndrome (Correct answer)
- Bartter syndrome
- Liddle syndrome
Correct answer: Fanconi syndrome
Tenofovir causes mitochondrial toxicity in proximal tubules, leading to Fanconi syndrome with generalized proximal tubular dysfunction.
Question 3: A 55-year-old woman develops oliguric AKI after prolonged hypotension during cardiac surgery. Urine microscopy shows muddy-brown granular casts. Urine sodium is 55 mEq/L and FENa is 3.2%. What is the mechanism?
- Glomerulonephritis from immune complex deposition
- Ischemic acute tubular necrosis (Correct answer)
- Pre-renal azotemia from volume depletion
- Obstructive nephropathy from surgical ligation
Correct answer: Ischemic acute tubular necrosis
Ischemic ATN follows prolonged hypoperfusion, manifesting as muddy-brown granular casts, high urine sodium (>40 mEq/L), and FENa >1% due to tubular injury.
Question 4: A 38-year-old woman with hypertension refractory to three medications has a serum potassium of 2.8 mEq/L and metabolic alkalosis. Aldosterone-to-renin ratio is 40 (ng/dL)/(ng/mL/hr). CT shows a 1.8 cm left adrenal adenoma. What is the best next step?
- Start spironolactone empirically
- Perform adrenal vein sampling (Correct answer)
- Proceed directly to left adrenalectomy
- Obtain MRI of the adrenals
Correct answer: Perform adrenal vein sampling
Adrenal vein sampling is required before surgery to confirm unilateral aldosterone hypersecretion, as CT can miss contralateral disease or misidentify non-functioning adenomas.
Question 5: A 30-year-old man with no past history develops cola-colored urine, periorbital edema, and hypertension 3 weeks after a streptococcal pharyngitis. C3 is low, C4 is normal. Renal biopsy would most likely show:
- Subepithelial (humps) deposits on electron microscopy (Correct answer)
- Mesangial IgA deposits on immunofluorescence
- Linear IgG along GBM on immunofluorescence
- Subendothelial deposits with wire-loop lesions
Correct answer: Subepithelial (humps) deposits on electron microscopy
Post-streptococcal GN shows subepithelial hump-shaped deposits on electron microscopy and granular IgG/C3 on immunofluorescence, with selective C3 consumption.
Question 6: A 65-year-old man with CKD stage 4 has serum bicarbonate of 16 mEq/L. He has muscle wasting and accelerated bone disease. What is the most appropriate treatment for his metabolic acidosis?
- Dietary protein restriction alone
- Oral sodium bicarbonate supplementation (Correct answer)
- Urgent dialysis initiation
- Potassium citrate only
Correct answer: Oral sodium bicarbonate supplementation
Oral sodium bicarbonate supplementation slows CKD progression, preserves muscle mass, and reduces bone disease by correcting the acidosis-driven protein catabolism.
Question 7: A 50-year-old man with Wegener granulomatosis (GPA) presents with hematuria, proteinuria, and rising creatinine. Renal biopsy shows a pauci-immune crescentic glomerulonephritis. Which antibody is most likely positive?
- Anti-GBM antibody
- ANA and anti-dsDNA
- c-ANCA (PR3-ANCA) (Correct answer)
- p-ANCA (MPO-ANCA)
Correct answer: c-ANCA (PR3-ANCA)
GPA (Wegener's) is associated with c-ANCA targeting proteinase 3 (PR3), while microscopic polyangiitis is more commonly p-ANCA/MPO-positive.
Internal Medicine Exam Nephrology and Kidney Injury 4
A 60-year-old man with gout and CKD has a serum uric acid of 11 mg/dL.
He starts allopurinol and develops a severe desquamating rash with hepatitis.
Which HLA allele is strongly associated with allopurinol hypersensitivity syndrome?