FRI255 Polyglandular Autoimmune Syndrome Type 2 Presenting With Severe Hyponatremia

Disclosure: A. West: None. A.N. Davis: None. A. Warner: None. S. Salcin: None. Introduction: Polyglandular autoimmune syndrome type 2 (PAS-2) is a polygenic autoimmune syndrome which presents with two or more specific autoimmune manifestations. The combination of Addison’s disease and Hashimoto’s thyroiditis has been referred to as Schmidt Syndrome. Treatment of hypothyroidism without recognition of concomitant adrenal insufficiency may result in exacerbation of adrenal insufficiency (AI). We present a case of PAS-2 presenting with severe hyponatremia. Case: A 28-year-old male presented to an outside hospital with fatigue and weakness. His sodium was 121mEq/L and TSH >356mcIU/mL, and he was admitted for management of hyponatremia. He was started on oral levothyroxine, urea tablets, and fluid restriction. In the weeks following discharge, the patient had worsening fatigue, weakness, dizziness, nausea, and weight loss, and he presented to our ED. His vital signs were stable without tachycardia or hypotension. He was lethargic but fully oriented. Hyperpigmented areas of the tongue and nose were noted. Laboratory evaluation revealed sodium 111mEq/L, potassium 4.5mEq/L, TSH 43.56 (0.4-4.7mcIU/mL), and free T4 of 1.12 (0.58-1.76ng/dL). He was admitted to the medical intensive care unit for management of severe hyponatremia. Repeat sodium was 112mEq/L with serum cortisol 4.57mcg/dL. Hypertonic saline was given without improvement in hyponatremia. Cortisol level was determined to be inappropriately normal in the setting of severe hyponatremia. Cosyntropin stimulation test was performed with baseline, 30 minute, and 60 minute cortisol levels of 5.31, 6.17, and 6.26, respectively, consistent with AI. ACTH level was not obtained due to the blood sample being hemolyzed. Other results include positive 21-hydroxylase antibody, TPO antibody >900 IU/mL, and undetectable GAD 65 antibody. He received IV stress dose steroids with resolution of his symptoms and his hyponatremia. Oral hydrocortisone replacement therapy was started prior to discharge. Discussion: Patients with one autoimmune endocrinopathy are at risk of developing a second one. Our patient’s hyponatremia was initially attributed to his hypothyroidism without recognition of concomitant AI. Early diagnosis of AI is important prior to initiation of levothyroxine, as treatment of hypothyroidism may exacerbate AI. The sodium level in our patient worsened from 121mEq/L at the previous admission to 111mEq/L when he presented to our hospital, related to worsening of his AI while being treated for his hypothyroidism. Timely diagnosis of associated AI requires high index of suspicion in such patients, particularly in patients with signs or symptoms which may overlap with hypothyroidism, such as hyponatremia in our patient. AI should be considered in any patient who presents with hyponatremia, even those who lack other classic features such as hypotension, hyperkalemia, and hypoglycemia. Presentation: Friday, June 16, 2023