Acute interstitial nephritis is most commonly caused by drug-induced hypersensitivity and presents with which combination of findings?

• A. Hemodynamic instability and hyaline casts
• B. Nephrotic-range proteinuria with lipiduria
• C. Obstructive uropathy with hydronephrosis
• D. Eosinophilic infiltration with fever, rash, eosinophilia, and sterile pyuria with WBC casts

Answer: (D)

Drug-induced hypersensitivity causes inflammation in the kidney interstitium, with eosinophils infiltrating the tissue and tubulitis. This leads to a recognizable set of findings: fever and rash from an allergic reaction, eosinophilia in the blood, and urinary signs of sterile pyuria with white blood cell casts due to interstitial inflammation and tubular involvement. Eosinophiluria is a helpful clue, often detected with a special stain, and together with the systemic allergic features, it points to acute interstitial nephritis rather than other kidney problems. The timing after exposure to common culprit drugs (like certain antibiotics, NSAIDs, or diuretics) supports the diagnosis. In contrast, the other scenarios reflect prerenal states (hemodynamic instability with hyaline casts), nephrotic syndrome (heavy proteinuria with lipiduria), or post-renal obstruction (hydronephrosis), which don’t match this interstitial inflammatory pattern. Management centers on stopping the offending drug and, if needed, short-term steroids to hasten recovery.