[A case of renal salt wasting syndrome progressing to severe hyponatremia after gemcitabine-cisplatin chemotherapy].

Renal impairment with a decreased glomerular filtration rate is a classical nephrotoxicity associated with cisplatin (CDDP). Renal salt wasting syndrome (RSWS), which is characterized by water and salt wasting, is a rare nephrotoxicity associated with CDDP. This syndrome shares many similarities with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Thus, it is important to differentiate between RSWS and SIADH because the treatment of one affects the pathogenesis of the other. Here, we report a case of RSWS after chemotherapy with CDDP. A 72-year-old man with bladder urothelial carcinoma (cT2N0M0) was admitted to our hospital for the first cycle of neoadjuvant chemotherapy with CDDP and gemcitabine. He was administered intravenous fluids on day 2 before chemotherapy. Five days later, he developed nausea, dysorexia, delirium, hyponatremia (serum sodium level 115 mEq/l), and renal dysfunction. Thus, we administered a normal saline infusion. Over the next 6 days, his serum sodium level increased to 137 mEq/l, and we stopped normal saline infusion. Three days after discontinuation of saline infusion, his serum sodium level again decreased to 128 mEq/l, and the next day, his systolic blood pressure dropped gradually between 70 and 80 mmHg. Therefore, we resumed the normal saline infusion, and after 3 days, his serum sodium level increased to 135 mEq/l and systolic blood pressure ranged between 110 and 130 mmHg. On the basis of dehydration and high urinary sodium excretion at the onset of chemotherapy, we diagnosed this clinical condition as RSWS. We abandoned neo-adjuvant chemotherapy, and performed total cystectomy and ileal conduit. Since 4 months after surgery, he has been free from recurrence and metastasis.