Levothyroxine as an Unusual Cause of Acute Interstitial Nephritis

Introduction: Acute interstitial nephritis (AIN), a common cause of acute kidney injury (AKI), is accompanied by histologic findings of interstitial inflammation, edema, and tubulitis. We report a patient who presented with AIN after starting levothyroxine, a medication used to treat hypothyroidism. Case Description: A 79-year-old male with a history of hypothyroidism and chronic kidney disease (CKD) presented with a two-week history of a painless, urticarial rash and intermittent diarrhea after starting levothyroxine. Laboratory findings were significant for a serum creatinine of 3.57 mg/dL, potassium of 5.6 mmol/L, CO2 of 11 mmol/L, and peripheral eosinophilia (eosinophils 12%). Serologic work-up showed normal levels of C3, C4, antinuclear antibodies, antineutrophil cytoplasmic antibodies, rheumatoid factor, and anti-glomerular basement membrane antibodies. Serum and urine protein electrophoresis was normal; however, urinalysis showed trace proteinuria. Renal ultrasound revealed echogenic kidneys consistent with CKD. The patient was diagnosed with AIN, and started on treatment for the AIN with IV Solu-Medrol (500 mg) for three days. He was discharged on a prednisone taper. The patient’s AKI, metabolic acidosis, and rash improved following IV steroids. He was switched from Mylan Levothyroxine to Armor Thyroid for thyroid supplementation at discharge. Discussion: Levothyroxine is a rare cause of AIN. AIN should be considered in cases of unexplained AKI, especially after new medication administrations. This case emphasizes the importance of considering levothyroxine as a cause of AKI and AIN. In addition, the offending agent should be discontinued upon a diagnosis of drug-induced AIN.