[A case of drug-induced granulomatous interstitial nephritis during the long course of Crohn's disease].

A 33-year-old man was diagnosed with Crohn's disease in 2001, and treated with mesalazine and ranitidine. Administration of infliximab was started in 2007 and led to a decrease in the activity of the Crohn's disease. He was referred to our department in the summer of 2011 following rapid progression of renal insufficiency, with serum creatinine levels increasing from 1.5 mg/dL to 4.3 mg/dL within 2 months. On admission, laboratory findings showed signs of inflammation, anemia, proteinuria, and hematuria. Renal biopsy results indicated the diagnosis of granulomatous interstitial nephritis. Neither clinical manifestations nor laboratory findings were suggestive of infectious disease, sarcoidosis, Wegener's granulomatosis or tubulointerstitial nephritis and uveitis. Mesalazine and ranitidine were discontinued in view of reports of drug-induced granulomatous interstitial nephritis. Levels of C-reactive protein immediately decreased, but renal function remained unimproved. Treatment with steroid pulse therapy was then initiated, followed by oral prednisolone at 40 mg/day, and his serum creatinine recovered to 2.3 mg/dL. Mesalazine and/or ranitidine appear to have been responsible for the granulomatous interstitial nephritis. In cases of Crohn's disease showing rapid deterioration of renal function, drug-induced renal disease should be considered, even if the drugs have been taken without apparent problems for a long duration.