Nephrology · USMLE Step 1 and Step 2

Acute Interstitial Nephritis song

Acute Interstitial Nephritis - Causes & Findings, as a song. Hear the short teaser here. The full song is on YouTube and Spotify.

Acute Interstitial Nephritis

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Key points in this song10

Acute interstitial nephritis (AIN) is most commonly caused by drugs, with NSAIDs, penicillins, cephalosporins, sulfonamides, rifampin, and proton pump inhibitors being classic culprits.
The classic triad of AIN includes fever, rash, and eosinophilia, but this full triad is present in fewer than one-third of cases; its absence does not exclude the diagnosis.
Urinalysis in AIN classically shows WBC casts, sterile pyuria, and eosinophiluria (detected with Hansel stain), distinguishing it from glomerulonephritis, which shows RBC casts.
AIN presents as acute kidney injury with elevated BUN and creatinine, but is typically non-oliguric and associated with a relatively bland urinalysis compared to glomerular disease.
Methicillin (a penicillin analogue) is the prototype drug associated with AIN via a type IV (T-cell–mediated) hypersensitivity reaction, not type I.
Sarcoidosis is a classic non-drug cause of AIN and should be suspected when AIN is accompanied by hypercalcemia, bilateral hilar lymphadenopathy, or elevated ACE levels.
Renal biopsy showing interstitial lymphocyte and eosinophil infiltration with tubular injury but intact glomeruli and vessels is the gold standard for confirming AIN.
Management requires immediate withdrawal of the offending agent; corticosteroids are used in refractory or biopsy-confirmed cases to accelerate renal recovery.
Prolonged or untreated AIN can progress to chronic tubulointerstitial nephritis with irreversible interstitial fibrosis and tubular atrophy, leading to chronic kidney disease.
NSAID-induced AIN is unique in that it may present without the classic allergic features (no rash or eosinophilia) and can be accompanied by nephrotic-range proteinuria due to concurrent minimal change disease.