Severe Hyponatremia Due to Cisplatin-induced Syndrome of Inappropriate Secretion of Antidiuretic Hormone

We report a rare case of severe hyponatremia due to cisplatin-induced syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in a 74-year-old male with a history of squamous cell carcinoma of the tongue who presented with a five days history of worsening confusion. He was found to have severe hyponatremia. His clinical and laboratory findings were consistent with hyponatremia due to SIADH. He was treated with fluid restriction and salt tablets after which his serum sodium markedly improved. Drugs including diuretics, antidepressants, antipsychotics are well known to cause hyponatremia. Cisplatin is a very common antineoplastic drug for solid tumors. Clinicians need to have prompt recognition of this rare side effect of cisplatin to prevent life-threatening hyponatremia.