[Possible contribution of disseminated Mycobacterium shigaense infection to development of splenic marginal zone lymphoma].

A 73-year-old male who underwent splenectomy was diagnosed with splenic non-caseating granuloma in May 201X, and sarcoidosis was disregarded from the differential diagnosis. Owing to the persisting inflammation, the patient was carefully followed up with no treatment. Four months post splenectomy, the patient was hospitalized due to progressive dyspnea. Chest computed tomography revealed an encapsulated pleural effusion and lymphocytic infiltration in the left lower lung, with subclavian and mediastinal lymphadenopathy. Although the patient was treated with antibiotics, his condition showed no improvement; therefore, prednisolone 40 mg was administered, resulting in lung lesion improvement. A re-examination of the tissue obtained from the previously removed spleen revealed splenic marginal zone lymphoma (SMZL), a specific low-grade, small B-cell lymphoma. As a result, the patient was treated with rituximab combined with chemotherapy. During the fifth course of the chemotherapy, a subcutaneous abscess appeared in the cervical region, and Mycobacterium shigaense was isolated from the pus discharge, suggesting that the splenic granulomatous lesion formed due to M.shigaense, and dissemination of the Mycobacterium infection occurred following splenectomy and chemotherapy, when the patient was immunosuppressed. Overall, we consider that SMZL developed because of chronic inflammation resulting from a nontuberculous mycobacterial infection.