Rituximab (RTX), an anti-CD20 monoclonal antibody used in treatment of hematologic and rheumatologic disease, depletes systemic and intestinal B-cells. Diarrhea is seen in ~15% of people. Case reports associated RTX with de novo inflammatory bowel disease (IBD). We aim to characterize clinical features and course of RTX-induced colitis. Methods: A retrospective cohort study of all patients with new-onset diarrhea after RTX at Mayo Clinic from 01/2006 to 06/2017. Those with diarrhea, concurrent/recent use of RTX in past year, and colon biopsy were included. Diagnosis of IBD or microscopic colitis (MC) before RTX or age<18 were excluded. Demographics, indication of RTX, colitis type and other variables were summarized as median and interquartile range (IQR) or percentage and proportions. Data was analyzed using JMP. Results: 460 patients (57% female, median age 57 years [IQR 43-68]) with RTX, diarrhea, and histology were evaluated. Of these, 23 (73.9% female, median age 63 years [IQR 38-72]) were identified RTX-induced colitis (Table 1): 60.8% IBD(8/23 CD, 6/23 UC) and 39.2%MC. Median daily bowel movements was 5 [IQR 3-14]. Most common symptoms along diarrhea were abdominal pain (65.2%) and weight loss (56.5%). Median time from first RTX dose to diarrhea was 20.3 months [IQR 11.3-76.5]. CD19 depletion was noted in all 11 who were tested at time of GI evaluation. Median of 3 months [IQR 4.6-25.2] diarrhea prior to initial GI evaluation. Among those with IBD, 85.7% (12/14) received IBD-directed therapy: 2 biologic monotherapy, 3 immunomodulators, 2 combo (biologic and immunomodulator), 3 5-ASA, and 2 budesonide. 2 required IBD-related surgery. RTX was stopped in 22/23 after diagnosis of RTX-induced colitis with complete improvement in symptoms in 13/22.Conclusion: RTX-induced colitis is rare but clinically significant. In our cohort, 5% with new onset diarrhea after RTX who underwent endoscopic evaluation had colitis. Diarrhea resolved in 60% after stopping RTX.
