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Difficulty: MediumFormulating a Differential Diagnosis

Match each clinical presentation of acute kidney injury with the most likely underlying diagnosis.

  • A hospitalized patient develops progressive oliguria three days after an episode of severe hypotension; urinalysis demonstrates muddy brown granular casts.Acute tubular necrosis
  • A patient develops a fever, maculopapular rash, and acute kidney injury two weeks after starting a proton pump inhibitor; urinalysis shows white blood cell casts.Acute interstitial nephritis
  • A young adult presents with hemoptysis, edema, and acute kidney injury; urinalysis reveals dysmorphic red blood cells and red blood cell casts.Acute glomerulonephritis
  • An elderly patient develops acute kidney injury, livedo reticularis, and blue toes a few days after undergoing percutaneous coronary intervention.Atheroembolic renal disease

Answer

The presentations map to their underlying pathophysiologic mechanisms: hypotension with muddy brown casts is acute tubular necrosis; PPI use with rash and WBC casts is acute interstitial nephritis; hemoptysis with RBC casts is acute glomerulonephritis; and post-catheterization livedo reticularis is atheroembolic renal disease.
Each clinical vignette contains pathognomonic historical and laboratory features that distinguish the specific etiology of intrinsic acute kidney injury from overlapping conditions.

Step-by-Step Solution

1
Evaluate the clinical history and urinalysis for the patient with prior hypotension.
Severe hypotension suggests ischemia. Muddy brown granular casts indicate acute tubular necrosis.
Ischemic injury to the renal tubules leads to shedding of necrotic epithelial cells into the urine, forming these classic casts.
2
Analyze the patient with a rash and fever after starting a proton pump inhibitor.
The triad of fever, rash, and WBC casts post-medication points to acute interstitial nephritis.
Proton pump inhibitors, NSAIDs, and antibiotics are classic triggers for hypersensitivity reactions in the renal interstitium.
3
Assess the presentation of hemoptysis and dysmorphic RBCs.
Pulmonary hemorrhage combined with nephritic urinary sediment suggests a pulmonary-renal syndrome like Goodpasture syndrome.
Glomerular inflammation allows RBCs to cross into the urine, becoming dysmorphic and clumping into casts.
4
Interpret the post-catheterization signs of livedo reticularis and blue toes.
These physical findings strongly indicate atheroembolic renal disease.
Catheter manipulation can mechanically dislodge cholesterol plaques from the aorta, causing microemboli to the kidneys and distal extremities.

Key Concept

Formulating a differential diagnosis for acute kidney injury using patient history, medication exposures, and diagnostic urine microscopy findings.
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Formulating a Differential Diagnosis

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