Severe hyponatremia due to hypopituitarism with adrenal insufficiency: Report on 28 cases

Severe hyponatremia due to hypopituitarism and adrenal insufficiency can be life-threatening. In our experience, the diagnosis of hypopituitarism in hyponatremic patients is often overlooked. In a retrospective study we screened the files of 185 patients with severe hyponatremia (<130 mmol/l) that had been seen in our endocrinological unit in order to describe the clinical spectrum of patients with hyponatremia and hypopituitarism. In 139 cases it was possible to clearly ascribe the patients to the pathophysiological groups of 1) primary sodium deficiency, 2) edematous disorders, and 3) normovolemic disorders including the Syndrome of Inappropriate ADH Secretion (SIADH). 28 patients with severe „normovolemic hyponatremia“ (mean serum sodium: 116±SD 7 mmol/l) had hypopituitarism and secondary adrenal insufficiency as shown by basal cortisol measurements and dynamic tests of adrenal function. In 25 cases of this group hypopituitarism (mostly due to empty sella, Sheehan’s Syndrome and pituitary tumors) had not been recognised previously, and in 12 cases recurrent hyponatremia during previous hospital admissions (up to four times) could be documented. The most frequently occurring clinical signs were missing or scanty pubic and axillary hair, pale and doughy skin and small testicles in the men. Frequent symptoms like nausea and vomiting, confusion, disorientation, somnolence or coma were similar to those in 91 patients with SIADH. In most patients with hyponatremic hypopituitarism, plasma ADH levels were inappropriately high, probably due to a failure of endogenous cortisol to suppress the hormone in a stressful situation. All patients recovered after low-dose hydrocortisone substitution. Most patients had other pituitary hormone deficiencies and were appropriately substituted subsequently. Hypopituitarism including secondary adrenal insufficiency seems to be a frequently overlooked cause of severe hyponatremia. A high level of suspicion is the best way to recognise the underlying disorder. Treatment with hydrocortisone is very effective.