PSAT037 The Unlikely Suspect - A New Diagnosis of Autoimmune Addison's Disease in an 80-year old Lady

INTRODUCTION: Hyponatremia is a common cause of hospitalization in older adults. Addison's disease (AD), an uncommon cause of hyponatremia, is primary adrenal insufficiency (AI) caused by autoimmune adrenalitis, infections, adrenal hemorrhage, or infiltration. Autoimmune adrenalitis is an uncommon cause of AD after age 60 years. We report an 80 year old patient with hyponatremia who was ultimately diagnosed with autoimmune AD. CASE REPORT: An 80 year-old lady with steroid-controlled asthma, presented to the ER with weakness, imbalance, nausea and vomiting two weeks after a urinary tract infection. Her blood pressure was 96/64 mm Hg with otherwise normal vital signs and unremarkable general examination. Laboratory evaluation revealed hyponatremia (Na 120 mmol/L), hyperkalemia (K 5.7 mmol/L) and acute kidney injury (creatinine 1.2 mg/dl, GFR 43 ml/min/m). Hyperkalemia resolved with intravenous fluids, insulin and dextrose therapy (K 4.7 mmol/L). However, hyponatremia persisted (Na 120-123 mmol/L) despite fluid restriction, normal saline, and salt tablets. Additionally, patient remained hypotensive with blood pressure between 90/40-120/60 mm Hg. Due to concern for AI from prior steroid use, morning cortisol was measured and was low (4.63 mcg/dl). Concurrent ACTH level was elevated (252 pg/ml, range 7.2-63.3 pg/ml). Cosyntropin stimulation test done during hospitalization was abnormal (4.5 mcg/d→6.7 mcg/dl→8 mcg/dl) confirming AD. At outpatient consultation with endocrinology, patient reported nausea and vomiting for 18 months prior to hospitalization, 50 lbs weight loss, weakness, short-term memory loss, and dizziness attributed to vertigo. Symptoms worsened a month prior to patient's hospitalization. Repeat cosyntropin stimulation test remained abnormal (8.5 mcg/dl→9.6 mcg/dl→10 mcg/dl). CAT scan of the abdomen with adrenal protocol was unremarkable for adrenal masses, hemorrhage, infiltration, or metastasis. Surprisingly, 21-hydroxylase antibody testing was positive confirming autoimmune AD. The patient has been on hydrocortisone 15 mg in AM + 5 mg in PM and fludrocortisone 0.1 mg daily for one year now with improvement in symptoms. DISCUSSION: Medications, poor diet, and diabetes are common causes of hyponatremia in the elderly. AD, an uncommon cause of hyponatremia, should be considered in a hospitalized hyponatremic elderly patient. Non-specificity of AD symptoms makes the diagnosis in this age group difficult, often causing delay in appropriate management. Autoimmune AD is characterized by the presence of 21-hydroxylase antibodies. Data on autoimmune AD incidence in the elderly is limited due to rarity. Our patient's autoimmune AD was likely masked due to steroid use for asthma. During COVID-19 pandemic, masking, and social distancing decreased the patient's steroid needs and unmasked AD after the UTI. Our case highlights the importance of considering autoimmune AD as a cause of AI even in the elderly. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.