The syndrome of inappropriate antidiuretic hormone secretion as a cause of hyponatremia in cystic fibrosis.

The syndrome of inappropriate secretion of antidiuretic hormone was observed in two patients with cystic fibrosis during acute exacerbation of chronic pulmonary disease. It was diagnosed by the accepted clinical and laboratory criteria and confirmed in one case by values for immunoreactive vasopressin that were inappropriately high for plasma osmolality. The severe hyponatremia was corrected by fluid restriction, alone or combined with intravenous treatment with diuretic and hypertonic saline solution. In addition, there was simultaneous therapy of the pulmonary disease. SIADH thus must be added to salt loss as a cause of hyponatremia in CF, and may be more common than realized in patients with CF and severe pulmonary disease.