Methotrexate (MTX), the first-line drug for rheumatoid arthritis, rarely causes malignant lymphomas, which have been reported as MTX-associated lymphoproliferative disorders (MTX-LPD). Herein, report a case of MTX-LPD in the ileum with fistula formation in the small bowel and rectum. At the end of January 2023, an 81-year-old man who had been taking MTX for rheumatoid arthritis since the age of 73 years complained of abdominal pain and was diagnosed with intestinal obstruction at a previous hospital. In the early February 2023, the patient was referred to our hospital for further examination and treatment. A computed tomography scan revealed a thickened terminal ileum wall and enlarged mesenteric lymph nodes. A retrograde double-balloon endoscopy (DBE) detected circumferential ulcerative lesions at the terminal ileum with deep depressions in parts of the ulcer base. In addition, submucosal tumor-like lesions with central depressions were observed in the rectum. Retrograde contrast imaging under DBE confirmed the presence of fistulae between the ileum and rectum. A biopsy of the ulcerative lesion revealed hyperplasia of germinal center cell-like cells, and immunohistochemistry demonstrated CD20 and CD79a positivity, but CD5, CD10, and cyclin D1 negativity. Ki-67 positivity was 90%, indicating B-cell lymphoma. Based on histopathological findings and patient's history, the patient was suspected to have MTX-LPD, resulting in ileal and high anterior rectal resection. Histopathological examination of the resected specimen revealed large atypical lymphocyte proliferation. Immunohistochemistry confirmed CD20 and CD79a positivity;CD5, CD10, and cyclin D1 negativity;a Ki-67 positivity rate of 70%;and Epstein-Barr virus-encoded small RNA in situ hybridization negativity, confirmming the MTX-LPD diagnosis, presenting as diffuse large B-cell lymphoma. Postoperatively, the patient was monitored with MTX discontinuation, and no recurrence occurred. The clinical course remained consistent with MTX-LPD.

A 66-year-old man was admitted to the hospital and diagnosed with mediastinal emphysema after an abnormal chest X-ray during physical examination. During hospitalization, an intestinal obstruction was observed to be caused by barium used during gastric cancer screening. Colonoscopy demonstrated stenosis and perforation due to sigmoid colon diverticulitis. Hartmann surgery was performed, and the patient was discharged on the 58th day. Therefore, colon perforation should be considered as a cause of mediastinal emphysema, and organic stenosis may occur with intestinal obstruction caused by barium.