The maintenance of normal plasma osmolality depends on the interaction of some complex mechanisms that regulates the extracellular fluid and sodium levels, involving antidiuretic hormone (ADH) actions, thirst, and the renin-angiotensin-aldosterone system. The hyponatremia may be caused by salt depletion, dilution mechanisms, or metabolic disturbances and is a frequent occurrence after the pituitary surgery, affecting 9 to 35% of these patients. Its causes can be the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) or, more frequently, the cerebral salt-wasting syndrome (CSWS). The clinical presentation of both syndromes is similar and the differential diagnosis may be difficult. The determination of the volemic state is essential for the diagnosis, since the patients with the SIADH are characterized for being euvolemic or hypervolemic, while those with CSWS are hypovolemic. Several methods are used to detect the volemic state of those patients, such as the determination of plasma and urinary osmolality, water deprivation test, hypertonic load test and the test of the furosemide that can be discriminatory for the SIADH and CSWS. The treatment of polyuric syndromes depends on their etiology, and includes vasopressin analogs (dDAVP), diuretics (chlorothiazide, hydrochlorothiazide and amiloride), and other drugs such as clorpropramide, hydroclorothiazide, clofibrate, glucocorticoids, carbamazepine and indomethacin. The treatment of SIADH needs fluid restriction and/or furosemide to reduce the extracellular volume. In contrast, the treatment of CSWS requires volume replacement with supply of sodium and liquids, and the fludrocortisone can be a good therapeutic alternative. The diagnosis and treatment of these syndromes are discussed in view of the literature.
Antidiuretic hormone; Hyponatremia; Diabetes insipidus; Syndrome inappropriate secretion of antidiuretic hormone; Cerebral salt wasting; Pituitary surgery
