[A case of drug-induced syndrome of inappropriate secretion of antidiuretic hormone].

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is characterized by hyponatremia, plasma hypo-osmolality, a urine sodium concentration >30-40 mmol/L, normal acid-base balance, a normal plasma potassium concentration and, frequently, hypouricemia. There are different types of SIADH: idiopathic, iatrogenic, and forms caused by central nervous system or lung disorders, neoplasia and major surgical interventions. Drug-induced SIADH is becoming the most frequent cause of hyponatremia encountered in clinical practice. Here we report the case of a 60-year-old man in a coma (I-II) and with very severe hyponatremia (99 mmol/L) due to SIADH induced by fluphenazine and amitriptyline, which he had been taking since many years as antidepressant drugs. SIADH became very quickly more severe due to the recent administration of cisplatin. There was rapid improvement of the clinical symptoms after withdrawal of the drugs involved and correction of hyponatremia. In conclusion, in rare cases like the present one hyponatremia related to SIADH may be so severe as to represent a true clinical emergency. The administration of drugs known to cause hyponatremia should be avoided, if possible; otherwise, very careful monitoring of the plasma sodium concentration is mandatory to avoid severe neurological complications which may lead to the death of the patient.