8252 Central Adrenal Insufficiency Masquerading as Syndrome of Inappropriate Antidiuretic Hormone (SIADH): A Case Report

Abstract Disclosure: J.G. Sazon: None. J.L. Reyes: None. J.V. Chua: None. S.A. Kho: None. Hyponatremia, the most common electrolyte imbalance encountered in clinical practice, has various causes and presentation. Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is a frequent hospital-related cause, potentially leading to misdiagnosis with adrenal insufficiency due to shared clinical features which may cause potential deleterious effect. We present a case of a 41-year-old male hyponatremic patient with a two-month history of progressive generalized body weakness and lightheadedness, initially managed as SIADH. Upon admission, the patient persistently showed low serum sodium level (122mmol/L) (NV: 135-145mmol/L), exhibited signs of euvolemic hyponatremia despite fluid restriction, intravenous furosemide, and sodium chloride tablets. Further work-up revealed normocytic normochromic anemia (Hgb 107 g/L) (NV: 120-160g/L), elevated ESR of (31mm/hr) (NV: 0-15mm/hr), low Ft4 (2.97 pmol/L) (NV: 12-22 pmol/L) and normal TSH (2.2 uIU/mL) (NV: 0.27-4.20 uIU/mL). During hospital stay, he experienced an episode of hypotension at 80/50mmHg and hypoglycemia at 65 mg/dL. Investigation revealed adrenal insufficiency secondary to pituitary macroadenoma with apoplexy as showed in magnetic resonance imaging. Patient was started on Prednisone. Pre-operatively, hydrocortisone 100mg IV every 8 hours preoperatively. He underwent transsphenoidal surgery; excising a 2.5cm soft and grayish suprasellar mass. Post-operatively, he was given Prednisone and Levothyroxine resulting in symptom improvement and normal sodium levels.The occurrence of hyponatremia due to adrenal insufficiency is relatively uncommon, emphasizing the need for heightened suspicion when assessing patients with prolonged or recurring hyponatremia. This paper highlight the need to replace glucocorticoid prior supplementation of thyroid hormone in such cases, averting the occurrence of adrenal crisis. This case indicated a mechanism of persistent hyponatremia attributed to secondary adrenal insufficiency, with added therapeutic benefits observed through the use of glucocorticoids and transsphenoidal surgery. Presentation: 6/1/2024