FRI262 Can Selective Serotonin Reuptake Inhibitors Unmask Underlying Polyglandular Autoimmune Syndrome Type II?

Disclosure: S. Dehghani: None. S. Kalik: None. J. Zaidan: None. A. Nisar: None. Background: Patients with chronic use of SSRIs are at increased risk of developing hyponatremia secondary to SIADH but a full work up to exclude other etiologies might still be warranted if patient has risk factors. Clinical Case: 63-year-old female with past medical history of rheumatoid arthritis and hypothyroidism secondary to Hashimoto thyroiditis presented to the hospital for evaluation of syncopal episodes associated with dizziness, loss of consciousness and weight loss. She was started three weeks prior to presentation on Escitalopram 10 mg for mild depression. On exam she had orthostatic hypotension, she looked tanned but there was no buccal or palmar pigmentation. Admission blood work showed Na level of (111 mmol/L, n:135-145 mmol/L), Potassium of (5.7 mmol/L, n: 3.5-5 mmol/L), Creatinine of (0.8 mg/dL, n:0.7-1.5 mg/dL). Urine Sodium was (59 mEq/L, n: 20 mEq/L) and Urine osm (306 mOsm/Kg, n:50-1200 mOsm/kg). TSH was normal and 8 AM cortisol level was (6.0 ug/dL, n: 6.0-18.4 ug/dL). Initially Hyponatremia was attributed to SIADH secondary to use of Selective Serotonin Reuptake inhibitors, however her autoimmune comorbidities, orthostatic hypotension and physical exam findings warranted more work up to rule out Adrenal insufficiency. The 250 mcg Cosyntropin Stimulation test was done with baseline cortisol of (4.6 ug/dL, n: 6-18.4 ug/dL) and cortisol at 30 minutes and 60 minutes of (5.2 ug/dL and 5.1 ug/dL respectively) confirming failure to respond to ACTH and diagnosis of adrenal insufficiency. She denied taking exogenous steroids. Later her ACTH came back very high (956 pg/mL, n:7-63 pg/mL), aldosterone was (5.3 ng/dL, n<23 ng/dL), plasma renin activity was high at (20.095 ng/mL/hr, n:0.1-1.3ng/mL/hr) and anti-adrenal antibodies were positive confirming the diagnosis of Addison disease. Patient was started on IV hydrocortisone with slow resolution of hyponatremia and symptoms. She was discharged on maintenance hydrocortisone and fludrocortisone. Given the presence of Hashimoto thyroid disease and Rheumatoid arthritis, patient was diagnosed as having polyglandular autoimmune Syndrome type II. Conclusion: The signs and symptoms of adrenal insufficiency are often nonspecific, resulting in long delays in diagnosis or even misdiagnosis. Hyponatremia is one of the manifestations of adrenal insufficiency which can be inevitably missed or misdiagnosed with syndrome of inappropriate antidiuretic hormone (SIADH) as both can manifest as euvolemic hyponatremia and inappropriate urinary Na concentration. This case demonstrates the importance of thorough investigation of underlying etiologies of patients with symptomatic hyponatremia who are also at risk SIADH secondary to SSRIs use. Presentation: Friday, June 16, 2023