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Difficulty: HardNephrology

Match each clinical and laboratory presentation with the most likely underlying nephrological etiology.

  • A 62-year-old man with fatigue, back pain, and hypercalcemia develops acute kidney injury. Urinalysis reveals trace protein on standard dipstick but is strongly positive on the sulfosalicylic acid (SSA) test.Multiple myeloma cast nephropathy
  • A 35-year-old man develops gross hematuria two days after the onset of a viral upper respiratory infection. Urinalysis shows dysmorphic red blood cells. Serum C3 and C4 complement levels are normal.IgA nephropathy
  • A 45-year-old woman with a history of Sjögren syndrome presents with profound muscle weakness. Laboratory studies show a serum potassium of 2.12.1 mEq/L, bicarbonate of 1414 mEq/L, and a normal serum anion gap. Urine pH is 6.56.5 and the urine anion gap is positive.Type 1 (distal) renal tubular acidosis
  • A 45-year-old man with a mechanical aortic valve and prolonged fever presents with new petechiae and acute kidney injury. Urinalysis reveals red blood cell casts. Serum C3 and C4 complement levels are decreased.Infective endocarditis-associated glomerulonephritis
  • A 50-year-old woman receiving intravenous piperacillin-tazobactam for pneumonia develops a diffuse maculopapular rash and acute kidney injury. Urinalysis demonstrates white blood cell casts and sterile pyuria.Drug-induced acute interstitial nephritis

Answer

Presentation 1 matches Multiple myeloma cast nephropathy. Presentation 2 matches IgA nephropathy. Presentation 3 matches Type 1 (distal) renal tubular acidosis. Presentation 4 matches Infective endocarditis-associated glomerulonephritis. Presentation 5 matches Drug-induced acute interstitial nephritis.
Each clinical presentation is matched based on pathognomonic findings: myeloma cast nephropathy shows a dipstick-SSA protein discrepancy; IgA nephropathy presents with synpharyngitic hematuria and normal complement; Type 1 RTA presents with NAGMA, hypokalemia, and a positive urine anion gap; endocarditis-associated GN presents with hypocomplementemia and RBC casts; and AIN presents with an allergic triad and WBC casts.

Step-by-Step Solution

1
Analyze the urinalysis protein discrepancy and clinical signs in presentation 1.
Trace dipstick but strongly positive SSA test, combined with hypercalcemia and back pain, indicates the presence of monoclonal light chains.
This is a classic pathognomonic finding for multiple myeloma cast nephropathy.
2
Evaluate the timing of hematuria relative to infection and complement levels in presentation 2.
Hematuria is concurrent with a viral infection (synpharyngitic) and C3/C4 levels are normal.
These specific findings distinguish IgA nephropathy from post-infectious glomerulonephritis, which typically occurs weeks later and presents with low C3 levels.
3
Assess the acid-base and electrolyte derangements in presentation 3.
Patient has a normal anion gap metabolic acidosis, profound hypokalemia, alkaline urine (pH 6.56.5), and a positive urine anion gap in the setting of Sjögren syndrome.
This points to a failure of distal tubular acid secretion, confirming Type 1 (distal) renal tubular acidosis.
4
Identify the systemic syndrome and correlating renal findings in presentation 4.
Fever, a mechanical valve, petechiae, acute kidney injury, RBC casts, and low complement levels.
This constellation is diagnostic of infective endocarditis complicated by immune-complex mediated glomerulonephritis.
5
Correlate the clinical triad and medication history in presentation 5.
Recent piperacillin-tazobactam use followed by a diffuse rash, acute kidney injury, and WBC casts.
This represents an allergic inflammatory response characteristic of drug-induced acute interstitial nephritis.

Key Concept

Differentiation of nephrological etiologies using classic clinical presentations, timing of symptoms, complement levels, acid-base profiles, and specific urinalysis findings.
Estimated Time:2m 30s
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Topics

Nephrology

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