Diagnosis of fibrillary glomerulonephritis suggests possible atypical familial Mediterranean fever in a patient with ulcerative colitis.

Fibrillary glomerulonephritis (FGN) is a rare glomerular disease that typically presents in middle age, and reports in young adults are uncommon. Herein, we describe the case of a 22-year-old woman with ulcerative colitis who was referred for evaluation of persistent proteinuria and microscopic hematuria. Kidney biopsy showed mild mesangial hypercellularity with increased mesangial matrix on light microscopy. Electron microscopy revealed randomly oriented, nonbranching microfibrils measuring approximately 20 nm in diameter within the mesangial areas. Immunohistochemistry for DnaJ heat shock protein family member B9 (DNAJB9) was positive in the glomeruli, confirming the diagnosis of FGN. Given the unusually young onset, the clinical course, and the presence of intestinal inflammatory lesions, an autoinflammatory disorder, specifically atypical familial Mediterranean fever (FMF), was suspected. Therapy with an angiotensin II receptor blocker was initiated for proteinuria, and colchicine was subsequently added while mesalazine was tapered. After treatment, urinary protein excretion decreased, and endoscopic and histologic bowel inflammation improved. This case highlights three practical points: DNAJB9 immunostaining is useful to establish FGN when classic ultrastructural features are present, FGN can occur in young adults, prompting evaluation for underlying systemic or autoinflammatory conditions, and in patients with intestinal lesions resembling inflammatory bowel disease, consideration of FMF may lead to colchicine therapy that benefits renal and gastrointestinal manifestations.