A Case of Methotrexate-Associated Lymphoproliferative Disorders of Anorectal Lesion

A 70-year-old male patient was admitted to our hospital complaining of anal pain. Endoscopic examination revealed an ulcerative lesion with necrotic tissue in the lower rectum and anal canal. Computed tomography revealed a thick wall of the lower rectum, and no mass lesion was detected in the liver, lung or lymph nodes. Pathological examination of a biopsy from the rectal ulcerative lesion showed lymphoid infiltration (group 2). Immunohistochemically, diffuse large B cell lymphoma (DLBCL) was confirmed using samples taken from the rectal biopsy. No reactivation of Epstein-Barr virus was present in Epstein-Barr virus encoded RNA (EBER) in in situ hybridization of tumor cells. The patient had been treated with methotrexate (MTX) due to rheumatoid arthritis (RA) for 5 years. We discontinued administration of MTX. The endoscopic findings after cessation of MTX gradually improved and the rectal ulcer completely healed and disappeared. Since that time, the patient has had no recurrence. The final diagnosis was methotrexate-associated lymphoproliferative disorder (MTX-LPD). Case reports of MTX-LPD in anorectal lesions are very rare in Japan.