[Difficulties in the differential diagnosis of hyponatremia presenting with severe neuropsychiatric symptoms].

Hyponatremia is the most frequent eletrolyte imbalance in hospitalized geriatric patient. The accompanying signs and symptoms can run a wide range and, therefore, these patients are usually admitted to various departments, i.e. neurology and/or traumatology first. Directed laboratory investigations demonstrate severe hyponatremia. Differential diagnosis can be very difficult and complex in the clinical settings. Firstly, spurious forms of hyponatremia have to be excluded, then the underlying cause should elucidated based on the patients hydration status and serum osmolarity. Hyponatremia can be divided into hyper-, hypo- and normovolemic forms. Moreover, it can be further classified as hypo-, iso- and hyperosmolar hyponatremias. The differentiation between renal and extrarenal salt wasting forms is hinged on the urine sodium concentration. Syndrome of inappropriate antidiuretic hormone secretion is the most common cause of normovolemic, hypoosmolar forms (named also as Schwartz-Bartter syndrome). The authors aimed to shed light on the often insurmountable difficulties of the diagnosis, differential diagnosis and appropriate treatment of this very frequent electrolyte imbalance by presenting a clinical case report. Their purported aim reflects upon the wide array of ethiopathogenesis of hyponatremia: various endocrine, renal diseases, inappropriateness of antidiuretic hormone secretion as well as the role of different medications (e.g. diuretics). This fine-tuned and intricate physiology of sodium metabolism could fortuitously be overturned by these mechanisms.