Differential diagnosis of hyponatremia induced by cisplatin-containing chemotherapy: syndrome of inappropriate secretion of antidiuretic hormone (SIADH) or renal salt wasting syndrome (RSWS)

Hyponatremia due to syndrome of inappropriate antidiuretic hormone secretion (SIADH) or gastrointestinal loss of sodium is sometimes seen during chemotherapy. However, hyponatremia due to renal salt wasting syndrome (RSWS) can rarely occur during cisplatin-containing chemotherapy. We report a case of a 65-year-old man with recurrent oropharynx cancer treated with cisplatin, docetaxel and 5-fluorouracil-containing chemotherapy who suffered from acute-onset consciousness disturbance due to hyponatremia just after administration of cisplatin. His serum sodium level was 109mmol/L, urinary sodium was 132mmol/L, and the urinary output in 6 h was 3700 mL. In other words, he had hyponatremia, hypernatriuria and the excessive urinary excretion of sodium; the diagnosis of RSWS was made. The patient was treated with supplement of sodium and isotonic solution with careful monitoring of serum sodium level. He responded to the treatment well and recovered from the hyponatremia episode in a few days without any complications. Because treatment for hyponatremia caused by SIADH or RSWS was totally different, i. e. water depletion for SIADH and sodium supplies for RSWS, it is important to make a correct diagnosis for hyponatremia seen during chemotherapy. In this report, we present a precise clinical data of RSWS patients and also summarize the key diagnostic features of RSWS which can help to differentiate from other hyponatremia syndromes.