Prompt efficacy of tolvaptan in treating hyponatremia of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) closely associated with rupture of a gastric artery aneurysm.

A 78-year-old man with abdominal pain was diagnosed with a rupture of a gastric artery aneurysm. The serum Na level promptly decreased from 135 to 110 mmol/L within several days. Brain magnetic resonance angiography revealed severe vasoconstriction of the cerebral basilar artery and anterior cerebral artery. There was neither dehydration nor edema. The plasma arginine vasopressin level was 3.3 pg/mL, despite hypoosmolality. These findings indicated a diagnosis of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) derived from severe vasoconstriction of the cerebral arteries. The administration of 7.5 mg of tolvaptan rapidly increased the serum Na level from 123 to 138 mmol/L within the first 24 hours, thereafter continuously maintaining a normal level. Treatment with tolvaptan corrected the patient's dilutional hyponatremia.