Symptomatic Syndrome of Inappropriate Antidiuretic Hormone Secretion in Pituitary Apoplexy: A Case Report and Literature Review

ABSTRACT Objective: We present a case and a review of relevant literature demonstrating that pituitary apoplexy rarely presents with syndrome of inappropriate antidiuretic hormone secretion (SIADH)-induced hyponatremia. We discuss management strategies, including consideration of pituitary surgery in the absence of visual disturbance if conservative management fails to control profound hyponatremia. Methods: Case report with literature review. Results: A previously healthy, 32-year-old female with a history of regular menses presented with fatigue, lethargy, severe headache, and intractable nausea with emesis. At presentation she was clinically euvolemic with intact visual fields and had hypoosmolar hyponatremia with serum sodium 109 mmol/L, serum osmolality 232 mOsm/kg, urine sodium 114 mmol/L, and urine osmolality 374 mOsm/kg. Her thyroid-stimulating hormone concentration was low normal, with a free thyroxine concentration of 0.6 ng/dL and a random serum cortisol measurement of 8.7μmg/dL. Pituitary magnetic resonance imaging revealed a macroadenoma potentially harboring a hemorrhagic component. Administration of hypertonic saline eliminated her symptoms within hours; however, she remained profoundly hyponatremic despite 72 hours of oral fluid restriction and treatment with glucocorticoids and levothyroxine. The patient underwent transsphenoidal resection, which resulted in an intraoperative rise in serum sodium and postoperative diabetes insipidus. Conclusion: Although hyponatremia as a consequence of central adrenal or thyroid insufficiency is prevalent in pituitary apoplexy, SIADH-associated hyponatremia in apoplexy is rare. If conservative approaches fail, treatment of pituitary apoplexy-induced SIADH with severe hyponatremia includes acute medical management of hyponatremia. Definitive strategies can be considered to control hyponatremia. In the few previously reported cases, SIADH was eliminated or improved by surgery; however, the risks of surgery may outweigh the benefits, as the present patient developed postoperative diabetes insipidus. Abbreviations: SIADH = syndrome of inappropriate antidiuretic hormone secretion TSH = thyroid-stimulating hormone T4 = thyroxine