Persistent malnutrition caused by Nihonkaiense diphyllobothriasis diagnosed during treatment of malignant lymphoma

A 72-year-old man with ileocecal lymphadenopathy was found to have Epstein-Barr virus-positive diffuse large B-cell lymphoma using open biopsy, and an ileostoma was created. R-CHOP-like chemotherapy was initiated, but his malnutrition did not improve. After 3 cycles of chemotherapy, a 2-m-long Cestoda was removed from the stoma and was identified as Diphyllobothrium nihonkaiense using mitochondria cytochrome c oxidase subunit 1 targeted polymerase chain reaction analysis. Although D. nihonkaiense infections are asymptomatic, the ileostomy was thought to have exacerbated the malabsorption in this patient. Parasitic infections are rare; however, they should be added to the differential diagnosis of malnutrition of unknown cause during chemotherapy for hematological malignancies.