Rituximab-associated colitis with colonic perforation requiring subtotal colectomy in systemic sclerosis.

Rituximab-associated colitis, a rare toxicity that may occur following prolonged latency, has nonspecific features. We report a 42-year-old female with diffuse cutaneous systemic sclerosis and interstitial lung disease whose last rituximab infusion was 195 days before admission. She developed diarrhea and abdominal pain; initial computed tomography revealed no intra-abdominal focus. On day 12, colonoscopy revealed erosions and ulcers from the cecum to the descending colon; cytomegalovirus testing was negative. Symptoms persisted; repeat colonoscopy on day 20 confirmed multifocal ulceration, suggesting cytomegalovirus colitis or severe Crohn's disease. By day 27, computed tomography showed ascending colon thinning, descending colon thickening, and haustral loss like ulcerative colitis. High-dose prednisolone was initiated owing to the inflammatory bowel disease-like process. Although clinical symptoms and inflammatory markers were improved, follow-up computed tomography revealed free air and perforation, necessitating emergency subtotal colectomy with ileostomy. Histology demonstrated ulcers extending to the subserosa, and noncaseating granulomas in the mucosa and submucosa. Immunohistochemistry demonstrated CD3-positive, CD20-negative, and CD4-predominant lymphocytic infiltration. This case highlights that rituximab-associated colitis may mimic inflammatory bowel disease, show prolonged latency, and progress to perforation despite apparent biochemical improvement, warranting early biopsy and careful radiologic follow-up. Rituximab-associated colitis should be considered even months following anti-CD20 exposure.