Improvement of Severe Colon Stricture after Rituximab Therapy for Concomitant Mucosa-associated Lymphoid Tissue Lymphoma in a Patient with Ulcerative Colitis.

Colorectal strictures are uncommon in patients with ulcerative colitis (UC). An extranodal marginal zone B-cell lymphoma of mucosa- associated lymphoid tissue (MALT) lymphoma is rarely involved in the colon but may be associated with inflammatory bowel diseases. A 41-year-old female with a six-year history of UC presented with a severe stricture of the sigmoid colon that prevented the passage of a colonoscope. A histological examination revealed non-specific inflammation and fibrosis without dysplasia or cancer. Despite conventional treatment, including mesalazine and azathioprine for one year after that visit, the stricture persisted. In addition, diffuse, edematous exudative inflammation and multiple shallow ulcers were observed in the distal rectum, revealing a MALT lymphoma testing positive for CD20, CD43, CD5, and Bcl-2, but negative for CD3, CD10, CD23, and cyclin-D1. Four weekly doses of rituximab were administered. Follow-up colonoscopy performed one month after treatment revealed slight improvement in the rectal lesion without remnant histological evidence of a MALT lymphoma. In addition, the stricture showed marked improvement, and the colonoscope could pass easily through the stricture site. This is the first case report on an improvement of a severe sigmoid colon stricture in a patient with UC after rituximab treatment for a concomitant rectal MALT lymphoma.