Crohn's Disease with Granulomatous Interstitial Nephritis as an Extraintestinal Complication from the Time of the Diagnosis.

Granulomatous interstitial nephritis (GIN) has been reported in <0.5% of patients with inflammatory bowel disease, and most cases of GIN are drug-induced. A 13-year-old boy was referred for the evaluation of abdominal pain, diarrhea, and weight loss. The patient was diagnosed with non-drug-induced GIN and Crohn's disease based on total colonoscopy and a biopsy of the colon and kidney. Both tissues contained macrophages and increased epithelial expression of IκBζ, a protein involved in the nuclear factor kappa-light-chain-enhancer of activated B cells pathway. There may be more patients with GIN complicated by Crohn's disease than expected, and macrophages may be involved in the pathogenesis.