A 61-year-old woman started on allopurinol two weeks ago presents with rising creatinine, fever, and a maculopapular rash. Urinalysis shows white blood cell casts. Which finding on renal biopsy would confirm the suspected diagnosis?
- A Interstitial edema with lymphocytes, macrophages, plasma cells, and prominent eosinophils sparing the glomeruli ✓
- B Amorphous eosinophilic material in vessel walls staining positive with Congo red
- C Necrotizing granulomas centered on the medulla with acid-fast bacilli
- D Patchy cortical infarction with fibrinoid necrosis of arcuate arteries
Correct answer: A. Interstitial edema with lymphocytes, macrophages, plasma cells, and prominent eosinophils sparing the glomeruli
Explanation
Drug-induced acute interstitial nephritis classically presents about one to two weeks after starting a new drug with fever, rash, arthralgia, and eosinophilia, plus sterile pyuria and WBC casts. Biopsy shows a patchy interstitial inflammatory infiltrate rich in T cells, macrophages, plasma cells, and eosinophils with tubulitis, while glomeruli are spared until late. Granulomatous interstitial nephritis lacks the eosinophil-predominant picture of drug hypersensitivity.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.