Idiopathic syndrome of inappropriate antidiuretic hormone secretion possibly related to advanced age.

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) as a cause of hypotonic hyponatremia is well recognized. The syndrome is commonly associated with cranial and thoracic infectious disease or malignancy. An idiopathic form of the syndrome has been reported, but poorly documented. Our patient, an 88-year-old man without any associated disease, had SIADH confirmed by a standard water load test. The pattern of antidiuretic hormone release corresponded to the "vasopressin leak" pattern. A review of ten cases of "idiopathic" SIADH showed that each of these cases has been associated with neuropsychiatric or other medical disturbances. We conclude that idiopathic inappropriate antidiuresis does exist and is a discrete category of SIADH. Data suggest that advanced age may be a risk factor for this disease. This syndrome may account for the increased susceptibility to hyponatremia among older patients.