Recurrent Hyponatremia With Central Endocrine Dysfunction: A Diagnostic Challenge

A 55-year-old man with a history of chronic hyponatremia presented with recurrent nausea, vomiting, and severe hyponatremia. Initial evaluation revealed features consistent with the syndrome of inappropriate antidiuretic hormone secretion (SIADH), including hypotonic hyponatremia with inappropriately concentrated urine. Further workup demonstrated concurrent central hypothyroidism and hypogonadotropic hypogonadism, prompting neuroimaging. MRI identified a 1.7 cm suprasellar cystic mass compressing the pituitary infundibulum. The patient underwent transsphenoidal cyst drainage, resulting in the resolution of hyponatremia and normalization of pituitary function. This case highlights the importance of evaluating structural pituitary pathology in patients with hyponatremia and multiple endocrine abnormalities, demonstrating how compressive lesions can mimic idiopathic SIADH. The rapid postoperative normalization of sodium and hormonal axes underscores the reversibility of such deficits with timely intervention.