Hyponatremia and pituitary adenoma: think twice about the etiopathogenesis

Pituitary adenomas may be the cause of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), although few cases have so far been reported. We described a case of hypotonic hyponatremia in a 76-yr-old man with a pituitary macroadenoma. He had a recent history of two syncopal attacks which had occurred in the last two months. Baseline assessment demonstrated a sodium serum level of 114 mEq/l. Clinically, the patient appeared euvolemic. Thyroid and adrenal function testing did not show any abnormality. Plasma and urinary osmolality (238 and 186 mOsm/kg, respectively) were in agreement with the diagnosis of SIADH. Accordingly, 3% hypertonic saline solution was started, followed by water intake restriction when natremia reached 126 mEq/l. A computed tomography (CT) scan of the chest revealed the presence of a 2-cm lesion in the azygos-esophageal recess. Because the nature of the lesion appeared uncertain, antibiotic therapy was initiated. After one month, a new CT scan did not show any evidence of the mediastinic mass. Sodium serum level was within the normal range (141 mEq/l) and remained stable thereafter, without fluid restriction. This case very well demonstrates that, in the presence of hyponatremia due to SIADH, more frequently associated co-morbidities (ie mediastinic diseases) have to be searched, even in the presence of a possible, yet rare, cause of this syndrome (ie pituitary adenoma).