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Macroprolactinoma Presenting With Hyponatremia; A Rare Case Report


 Background: Hyponatremia is a common electrolyte abnormality, investigating the etiology can be challenging to the clinician, especially when the cause has rarely been associated with hyponatremia. Macroprolactinoma has rarely been reported as a cause of hyponatremia. We are reporting a case of macroprolactinoma presenting with hyponatremia.
 Care Report: A 67 year old female previously healthy female, presented with a fall due to syncopal episode. Patient reported lightheadedness for a week prior to presentation. On physical examination, patient had bilateral periorbital ecchymoses, and swelling of the nose. Remaining of physical exam was unremarkable. Lab work showed hyponatremia with high urine osmolality and high urine sodium, consistent with syndrome of inappropriate antidiuretic hormone (SIADH). CT head showed Intrasellar soft tissue mass represents a pituitary macroadenoma. Pituitary hormonal workup showed high prolactin: 2,808 ng/mL, the rest of pituitary profile was normal, including pituitary-adrenal axis evaluation. Pituitary MRI confirmed a large pituitary macroadenoma measuring 1.7 x 2.9 x 2.5 cm, which displaces and compresses the optic chiasm and invades the right cavernous sinus. She was treated with fluid restriction and salt tablets with improvement of sodium level to normal. Cabergoline 0.25 mg twice a week was started with improvement of prolactin level to 156 ng/mL over 9 months period.
 Discussion: Pituitary macroadenoma rarely associated with hyponatremia, and when reported it is usually secondary to hypopituitarism (low ACTH or low TSH). However, there are few cases reported of SIADH related hyponatremia in the presence of normal pituitary function. Although the exact mechanism of exaggerated production of arginine vasopressin (AVP) is not fully understood, the likely theory thought to be related to the mechanical pressure on the axonal terminal of AVP neurons by the large pituitary tumor.
 Conclusion: Hyponatremia due to SIADH has been linked in few cases with nonfunctioning pituitary adenoma. Only two cases found in the literature reporting SIADH secondary to prolactin producing pituitary adenoma, with our case being the third reported case.