Hyponatremia as the Initial Presentation of Evolving Pituitary Apoplexy

Abstract Pituitary apoplexy (PA) is a known, often under-recognized medical emergency and is characterized by ischemic or hemorrhagic necrosis of the pituitary gland. It is a rare clinical syndrome that occurs in 2-12% of pituitary tumors. Hyponatremia can occur secondary to hypocortisolism (12-40%) or, rarely, to the syndrome inappropriate antidiuretic hormone (ADH) secretion. We present the case of a 69-year-old man who presented with altered mental status on post-operative day 3 from total knee replacement surgery. Initial testing revealed hyponatremia of 124 mmol/L, low serum osmolality of 266 mOsm/kg, and high urine osmolality of 664 mOsm/kg with urine sodium of 179 mmol/L. Head computerized tomography revealed a sellar mass of 1.8 x 2.4 cm. Initial testing revealed low prolactin (0.7 ng/mL), normal TSH (0.458 mcIU/mL) with borderline low free T4 of 0.72 ng/dL. Morning cortisol was 12.7 mcg/dL with ACTH of 8.5 pg/mL. Cosyntropin stimulation test was done revealing baseline cortisol of 5.8 mcg/dL (at midnight), increasing to 25.8 mcg/dL after 30 minutes and to 30.9 mcg/dL 60 minutes after cosyntropin administration. His sodium and mental status initially improved with fluid restriction and salt tablets, for the assumed syndrome of inappropriate ADH secretion. The patient remained hemodynamically stable. On the fourth day, however, his mental status deteriorated. Magnetic resonance imaging revealed expansion of sella with hyperintense mass 2.2 x 2.0 x 2.8 cm with compression of the optic chiasm. He was given stress dose hydrocortisone and levothyroxine and underwent emergency transsphenoidal resection. Biopsy revealed acute hemorrhage within infarcted adenoma. Postoperatively, both the patient’s sodium and mental status improved significantly and he was discharged to home on hydrocortisone and levothyroxine. The main clinical concern in the management of PA remains under-diagnosis at presentation. Prognosis is dependent on management during the acute phase. PA can present as hyponatremia even in the absence of overt hypocortisolism, presumably due to inappropriate ADH secretion. Therefore, PA should be considered as one of the differential diagnoses in hemodynamically stable patients with altered mental status and hyponatremia.