MD Renal and Urinary Systems 5 — Questions and Answers
Question 1: A patient with multiple myeloma develops acute kidney injury. Light chain casts in tubules are noted on biopsy. What is this condition called?
- Amyloid nephropathy
- Cast nephropathy (myeloma kidney) (Correct answer)
- Light chain deposition disease
- Cryoglobulinemic nephritis
Correct answer: Cast nephropathy (myeloma kidney)
Cast nephropathy (myeloma kidney) occurs when monoclonal light chains precipitate with Tamm-Horsfall protein in tubules, causing obstruction and AKI.
Question 2: A patient on tacrolimus after a renal transplant develops a rising creatinine. Biopsy shows tubular vacuolization and arteriolar hyalinosis. What is the cause?
- Acute rejection
- Calcineurin inhibitor nephrotoxicity (Correct answer)
- BK polyomavirus nephropathy
- Chronic antibody-mediated rejection
Correct answer: Calcineurin inhibitor nephrotoxicity
Calcineurin inhibitors (tacrolimus, cyclosporine) cause nephrotoxicity manifesting as tubular vacuolization and arteriolar hyalinosis on biopsy.
Question 3: Which glomerular disease is associated with Heymann nephritis in rats and is the most common cause of nephrotic syndrome in adults?
- Focal segmental glomerulosclerosis
- Membranous nephropathy (Correct answer)
- Minimal change disease
- Membranoproliferative GN
Correct answer: Membranous nephropathy
Membranous nephropathy, caused by anti-PLA2R antibodies forming subepithelial immune complexes, is the leading cause of nephrotic syndrome in non-diabetic adults.
Question 4: A patient has metabolic acidosis with a normal anion gap, hyperchloremia, and urine pH persistently above 5.5 despite acidemia. Which type of RTA is this?
- Type I (distal) RTA (Correct answer)
- Type II (proximal) RTA
- Type III RTA
- Type IV RTA
Correct answer: Type I (distal) RTA
Type I (distal) RTA is characterized by inability to acidify urine (pH >5.5) due to defective H+ secretion in the collecting duct, causing hyperchloremic metabolic acidosis.
Question 5: Free water clearance (CH2O) is negative in a patient. What does this indicate?
- Patient is excreting dilute urine relative to plasma
- Patient is excreting concentrated urine and retaining free water (Correct answer)
- Patient has diabetes insipidus
- Patient's GFR is below normal
Correct answer: Patient is excreting concentrated urine and retaining free water
Negative free water clearance means the kidney is excreting urine more concentrated than plasma, retaining free water (as in SIADH or normal ADH response to dehydration).
Question 6: A 25-year-old with hematuria and sensorineural hearing loss has a family history of renal failure. Biopsy shows thinning and splitting of the GBM in a 'basket-weave' pattern. What is the diagnosis?
- Thin basement membrane disease
- Alport syndrome (Correct answer)
- IgA nephropathy
- Anti-GBM disease
Correct answer: Alport syndrome
Alport syndrome (X-linked, COL4A5 mutation) presents with hematuria, sensorineural deafness, and ocular abnormalities with characteristic GBM lamellation on EM.
Question 7: A patient has hyponatremia, inappropriately concentrated urine (>100 mOsm/kg), and normal volume status with no edema or dehydration. Serum uric acid and BUN are low. What is the diagnosis?
- Cerebral salt wasting
- Hypothyroidism
- SIADH (Correct answer)
- Psychogenic polydipsia
Correct answer: SIADH
SIADH presents with euvolemic hyponatremia, concentrated urine despite low serum osmolality, and dilute serum markers (low BUN, uric acid) due to water retention.
MD Renal and Urinary Systems 5
A patient with multiple myeloma develops acute kidney injury.
Light chain casts in tubules are noted on biopsy.
What is this condition called?