De Novo Colitis Associated With Rituximab in 21 Patients at a Tertiary Center

Rituximab, a monoclonal antibody directed against the CD20 antigen on B lymphocytes, is commonly used in the treatment of hematologic malignancies and rheumatologic disorders.1,2 It acts to rapidly deplete the B lymphocyte population through multiple mechanisms, leading to dysregulation of the immune system.3 Rituximab has been associated with numerous adverse gastrointestinal effects including diarrhea and bowel perforation, and recent reports have associated rituximab with the development of de novo inflammatory bowel disease (IBD).4,5 To our knowledge, there have been no reports of microscopic colitis (MC) associated with rituximab therapy. We aimed to identify patients with rituximab-associated colitis, and to better characterize the clinical features and disease course of these patients.