Apparent idiopathic hyponatremia in an ambulatory geriatric population

The purpose of this descriptive analysis is to demonstrate that among older patients with hyponatremia, there is a subset with apparent hyponatremia of the syndrome of inappropriate antidiuretic hormone secretion (SIADH) type, which appears associated with the aging process. A retrospective chart review was done to identify patients with hyponatremia and to classify them into non-SIADH, SIADH, and idiopathic categories.

The participants were the ambulatory population of The Mount Sinai Hospital's outpatient geriatric clinic. Pertinent data generated during the antecedent 24 months were collected from outpatient charts and included sets of laboratory values (consisting of one sodium, glucose, BUN and creatinine level), age, sex, race, clinical history, present diagnosis, medications, and prescribed diets for each patient in the total population.

Patients demonstrating hyponatremia with serum sodium levels of less than 135 mEq/L were identified from the total population and were further divided into SIADH and non-SIADH etiologies. The SIADH patients were then subdivided into known etiology SIADH and apparent idiopathic SIADH. In an ambulatory geriatric population of 405 subjects, 46 had hyponatremia, with SIADH the apparent cause in 27. Of the SIADH population, seven patients were considered to have idiopathic SIADH. An apparent predilection for development of this syndrome was observed among non-black patients and the old old.

The results support the hypothesis that aging is a risk factor for the development of SIADH-like hyponatremia in a subset of older patients who do not have an apparent underlying etiology. Thus, aging may be an independent etiology for the development of hyponatremia.