[Severe idiopathic hyponatremia caused by ADH inappropriate secretion in the elderly]

We report on seven elderly patients with severe hyponatremia (plasma sodium < 125 meq/l). All were symptomatic for central nervous system disturbances, weakness, nausea/vomiting and met clinical and laboratory criteria for the diagnosis of inappropriate secretion of antidiuretic hormone (SIADH). Investigations performed to determine the etiology of the syndrome gave negative results, so that the form was considered to be idiopathic. TC scans or MNR showed brain atrophy and/or chronic ischemic lesions. According to the scant series found in the literature, we believe that aging itself may be a risk factor for SIADH. Lowering of the osmolal threshold and/or reduced receptors sensitivity to osmotic stimula, induced by ischemic changes in the hypothalamic region, can represent the underlying mechanisms.