APPARENT IDIOPATHIC HYPONATREMIA IN AN AMBULATORY GERIATRIC POPULATION

OBJECTIVES: The purpose of this descriptive analysis is to demonstrate that among older patients with hyponatremia, there is a subset with a pparent hyponatremia of the syndrome of inappropriate antidiuretic hor mone secretion (SIADH) type, which appears associated with the aging p rocess. A retrospective chart review was done to identify patients wit h hyponatremia and to classify them into non-SIADH, SIADH, and idiopat hic categories. DESIGN: The participants were the ambulatory populatio n of The Mount Sinai Hospital's outpatient geriatric clinic. Pertinent data generated during the antecedent 24 months were collected from ou tpatient charts and included sets of laboratory values (consisting of one sodium, glucose, BUN and creatinine level), age, sex, race, clinic al history, present diagnosis, medications, and prescribed diets for e ach patient in the total population. RESULTS: Patients demonstrating h yponatremia with serum sodium levels of less than 135 mEq/L were ident ified from the total population and were further divided into SIADH an d non-SIADH etiologies. The SIADH patients were then subdivided into k nown etiology SIADH and apparent idiopathic SIADH. In an ambulatory ge riatric population of 405 subjects, 46 had hyponatremia, with SIADH th e apparent cause in 27. Of the SIADH population, seven patients were c onsidered to have idiopathic SIADH. An apparent predilection for devel opment of this syndrome was observed among non-black patients and the old old. CONCLUSIONS: The results support the hypothesis that aging is a risk factor for the development of SIADH-like hyponatremia in a sub set of older patients who do not have an apparent underlying etiology. Thus, aging may be an independent etiology for the development of hyp onatremia.