Interstitial Nephritis Following an Acute Acetaminophen Overdose

Background: Acute tubular necrosis (ATN) is the recognized injury responsible for renal dysfunction that may occur with an acetaminophen (APAP) overdose. We report a case in which acute interstitial nephritis (AIN) was responsible. Case Report: A 17-yr-old healthy female presented 2 days after ingesting nearly 15 grams of APAP, some in the formulation Tylenol PM (APAP/diphenhydramine). She initially had normal vitals and was tender to palpation in the RUQ. Initial lab testing: APAP 12.8 mcg/mL, AST 16023 U/L, INR 2.7, BUN 13 mg/dL, and Cr 0.7 mg/dL. Admission urinalysis (UA) revealed 27 RBCs/hpf, 20 WBCs/hpf, and no casts. IV N-acetylcysteine was begun and her liver dysfunction peaked the following day (AST 20921 U/L, INR 5.8) before progressive resolution. However, the patient developed a fever (without rash or eosinophilia), oliguric renal failure, and on the 2nd day of hospitalization hemodialysis (HD) was initiated (peak Cr 8.4 mg/dL prior to HD). A renal biopsy performed after 8 sessions of HD revealed AIN with tubular degeneration, interstitial edema, and mixed inflammatory cell infiltration with numerous eosinophils. Additional workup included a normal renal US, no growth of urine and blood cultures, a negative HIV test, and normal ANA. Steroid administration was begun and 3 weeks following the overdose, her renal function was normal. Case Discussion: Renal dysfunction in the setting of acute APAP poisoning has been well described as stemming from ATN. Occasionally, in the setting of hepatic failure, the hepatorenal syndrome may also occur, a diagnosis of exclusion characterized by a normal UA and biopsy. AIN may be associated with fever, rash, eosinophilia, and urine eosinophils, RBC's, WBC's, and WBC casts. AIN has only rarely been associated with APAP use, and to our knowledge never in the setting of acute overdose or in association with diphenhydramine. The identification of AIN in this case impacted management, as unlike ATN, AIN may benefit from steroid treatment Conclusion: We report a case of AIN following an acute APAP overdose. Recognition that it was not ATN led to specific treatment with steroids.