MON-067 From Severe Hyponatremia to Pituitary Macroadenoma: A Case of Pan-Hypopituitarism

Abstract Disclosure: M. Asfaw: None. A. Garg: None. P. Chalasani: None. D. Salvi: None. M. Obeidat: None. J. Aschemeyer: None. Introduction Hyponatremia is a common electrolyte disturbance with various causes, including endocrine disorders. Severe hyponatremia without an obvious cause requires further investigation. SIADH, often associated with pituitary adenomas, is a rare but important etiology. This case describes a 67-year-old male with severe hyponatremia, later diagnosed with a pituitary macroadenoma. Clinical Case A 67-year-old male with a history of hypertension and BMI 31.3 presented to the emergency department with a 1-week history of increasing fatigue, confusion, and vomiting. Upon examination, the patient was alert but demonstrated mild confusion. He denied any associated headache, visual changes, or seizures. Vital signs were stable, and there were no signs of volume depletion. He was oriented to person, place, and time, with no focal deficits. Laboratory findings revealed sodium of 115 mmol/L (135-145). His cortisol level was 4.8 mcg/dL (6.7-22.6), raising suspicion for adrenal insufficiency. Serum osmolality was 238 mOsm/kg, while urine osmolality was 393 mOsm/kg, suggesting SIADH. Additionally, TSH was 0.52 mcIU/mL (0.45-5.33), free T4 was 0.48 ng/dL (0.61-1.24), and testosterone was 37 ng/dL (175-781), with DHEA at 32.7 mcg/dL (24-244), indicating hypothyroidism and hypogonadism. These findings were highly suggestive of pan-hypopituitarism due to a pituitary adenoma. MRI revealed a heterogeneously enhancing mass consistent with a pituitary macroadenoma measuring 1.5 x 1.8 x 2.0 cm, displacing the pituitary parenchyma and stalk to the right, with moderate mass effect on the optic chiasm and nerves, especially on the right side. The diagnosis of pituitary macroadenoma causing SIADH and pan-hypopituitarism was confirmed. The mass likely caused adrenal insufficiency, hypothyroidism, hypogonadism, and SIADH, contributing to severe hyponatremia. The patient was managed in the ICU with intravenous fluids to gradually correct the hyponatremia and started on prednisone for adrenal insufficiency. Thyroid hormone and testosterone replacement were initiated. As sodium levels normalized and confusion improved, cortisol levels were monitored, and hormone replacement was adjusted. The neurosurgery team was consulted for possible surgical resection, with follow-up arranged for endocrinology and neurosurgery. Conclusion This case underscores the importance of considering pituitary macroadenomas as a potential cause of severe hyponatremia in patients with unexplained electrolyte disturbances. The SIADH caused by the pituitary mass, along with pan-hypopituitarism, contributed to the patient’s hyponatremia and hormonal deficiencies. Early recognition through lab investigations and MRI enabled timely hormone replacement therapy. This highlights the need for a thorough workup in patients with unexplained hyponatremia and endocrine abnormalities. Presentation: Monday, July 14, 2025