An unusual cause of syndrome of inappropriate antidiuretic hormone secretion.

A 22-year-old woman was admitted to intensive care with severe hyponatraemia. She suffered from lower abdominal pain, vomiting and irritability since one week. Physical findings showed euvolemia and an altered mental status with severe agitation and slurred speech. Abdominal examination was painful but there were no signs of peritonitis. Laboratory data were compatible with the diagnosis of syndrome of inappropriate secretion of antidiuretic hormone. Since patient was in a premenstrual phase, recently started to take an oral contraceptive and since no abnormalities were seen on an abdominal CT scan, the presentation was considered suggestive of an acute porphyria attack. A urinary sample indicated markedly increased levels of delta-aminolevulinic acid, porphobilinogen and uroporphyrin. A low activity of the porphobilinogen deaminase enzyme confirmed the diagnosis of acute intermittent porphyria. The present case demonstrates the need for a high level of suspicion in order to diagnose this disorder in unexplained syndrome of inappropriate antidiuretic hormone secretion and prevent life-threatening complications.