Primary Diffuse Large B-Cell Lymphoma of the Rectum in a Non-Immunosuppressed Patient with Ulcerative Colitis.

Introduction: The incidence of primary colorectal lymphoma in the gastrointestinal tract is very low, the rectum being infrequently affected. The development of this entity in inflammatory bowel disease patients usually occurs in a context of immunosuppression-based therapy, with only a few case reports describing its development in patients presenting no known risk factors. Moreover, the clinical presentation of primary colorectal lymphomas may be difficult to distinguish from an acute flare of ulcerative colitis (UC). Case Presentation: We present a case of non-Hodgkin lymphoma of the rectum in a 42-year-old male with a 7-year history of UC and no previous exposure to immunomodulatory agents. He presented with a history of mucous diarrhoea, tenesmus, proctalgia and weight loss, refractory to optimized therapy. A lower gastrointestinal endoscopy was performed revealing a circumferential ulcerated lesion of the rectum, from which histopathological analysis established the diagnosis of a non-Hodgkin diffuse large B-cell lymphoma (DLBCL). Discussion/Conclusion: The present case suggests the existence of alternative mechanisms for the development of DLBCL in UC patients. The clinical presentation mimicking an acute flare of UC posed a diagnostic challenge, highlighting the complexity behind the management of UC patients.