A 38-year-old man develops acute kidney injury (creatinine rising from 0.9 to 3.8 mg/dL over 4 days) after starting vancomycin and piperacillin-tazobactam for a soft tissue infection. Urinalysis shows sterile pyuria and white cell casts. Urine eosinophils are positive (Hansel stain). Kidney biopsy would most likely show:
- A Acute tubular necrosis with flattened tubular epithelium and granular casts
- B Mesangial proliferation with IgA deposits
- C Diffuse interstitial infiltrate with eosinophils and tubulitis — acute interstitial nephritis ✓
- D Crescentic glomerulonephritis with fibrinous crescents
Explanation
Drug-induced acute interstitial nephritis (AIN) typically presents 5-10 days after starting the offending drug (antibiotics are a common cause, especially beta-lactams and vancomycin). The classic triad is fever, rash, and eosinophilia, though this is present in <30% of cases. Urinalysis typically shows sterile pyuria, white cell casts (tubulitis), and urine eosinophiluria. Biopsy shows diffuse interstitial edema with mononuclear cell (and eosinophil) infiltration with tubulitis. ATN shows granular/pigmented casts with epithelial cell injury, not eosinophilic infiltration.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.