Hyponatremia as the Initial Presentation of Rathke's Cleft Cyst-Related Hypopituitarism.

Rathke's cleft cyst (RCC) is a benign sellar lesion that is frequently detected incidentally, while symptomatic cases are uncommon. Endocrine dysfunction may occur due to compression of the pituitary gland, but profound hyponatremia as the initial manifestation of RCC-related hypopituitarism is rare and may delay diagnosis. We report the case of a 76-year-old woman who presented with persistent dizziness and severe euvolemic hyponatremia. Further endocrine assessment demonstrated secondary adrenal insufficiency, central hypothyroidism, hypogonadotropic hypogonadism, and mild hyperprolactinemia. Magnetic resonance imaging revealed an RCC with mild suprasellar extension and pituitary stalk deviation. The patient was treated with hydrocortisone followed by levothyroxine, resulting in clinical improvement and normalization of sodium levels. Although transsphenoidal surgery was recommended, she declined operative management and remained clinically stable with hormone replacement therapy during six months of follow-up. This case highlights that RCC-related hypopituitarism should be considered in patients presenting with unexplained euvolemic hyponatremia, even in the absence of headache, visual disturbances, or other classical sellar symptoms. Early endocrine evaluation and pituitary imaging are essential to establish the diagnosis, initiate appropriate hormone replacement, and prevent recurrent hyponatremia and potentially life-threatening adrenal insufficiency.