[Life-Threatening Hyponatremia by Chemotherapy in a Patient with Non-Hodgkin's Lymphoma].

Cyclophosphamide and vincristine are known to be the chemotherapeutic agents most frequently associated with hyponatremia. Here, we report the case of a 69-year-old man with non-Hodgkin's lymphoma who developed severe hyponatremia during chemotherapy. The Japanese man was diagnosed with diffuse large B-cell lymphoma, and underwent chemotherapy treatment with THP-COP (cyclophosphamide, pirarubicin, vincristine, and prednisolone). In the first course of chemotherapy, he developed hyponatremia (nadir 109 mEq/L) and his urinary N-acetyl-β-D-glucosaminidase (NAG) level had increased. After the second courses of chemotherapy with rituximab, pirarubicin, and prednisolone, without cyclophosphamide and vincristine, he had developed light hyponatremia (nadir 130 mEq/L). However, after the third and fourth courses of chemotherapy with rituximab, pirarubicin, prednisolone, and cyclophosphamide, he had developed a medium level of hyponatremia (nadir 124-125 mEq/L) and his NAG level had increased further. The possible mechanism of this phenomenon is due to renal tubular damage by cyclophosphamide. We conclude that extra caution is necessary if a patient develops severe hyponatremia following chemotherapeutic treatment with cyclophosphamide and vincristine.