MON-LB038 Isolated Hypoaldosteronism Due to Autoimmune Adrenalitis in a Patient With Autoimmune Polyglandular Syndrome

BACKGROUND At the initial presentation of autoimmune adrenal insufficiency, most patients present with hormonal deficiencies from all three layers of adrenal cortex. However, isolated aldosterone deficiency causing a true partial adrenal insufficiency in the setting of autoimmune adrenalitis remains underrecognized. CASE REPORT A 67-year old female patient with a known history of diabetes mellitus type 1 since the age of 13 and morphea, presented with progressively worsening symptoms of confusion and hallucinations, fatigue, and loss of appetite over the past 5 years. During this time, she has had frequent and recurrent episodes of mild intermittent hyponatremia with hyperkalemia requiring intravenous fluids and ingested salt tablets, especially when she felt more symptomatic. On her initial evaluation here, she presented with hyponatremia (125 mmol/l, n: 135-145 mmol/l), low osmolality (264 mOsm/kg, n: 275-295 mOsm/kg), and normal potassium level (3.6 mmol/l, n: 3.6-5.2 mmol/l). Further investigations drawn at the same time revealed a low aldosterone (<4 ng/dL), normal renin (5.3 ng/mL/hr, ref 2.9-10.8), normal serum cortisol level (and normal response to Cortrosyn stimulation), though all in the setting of positive antibodies against 21-hydroxylase. Pan-imaging revealed no evidence of malignancy that can be causing ectopic SIADH production. Additional testing showed presence of auto antibodies contributing to pernicious anemia and thyroid disease. Treatment was started with fludrocortisone 0.1 mg tablet daily and she was advised to take the salt tablets only if she has any symptoms. The patient’s symptoms have resolved 8 months since this diagnosis, with normalized sodium and potassium levels. CONCLUSION Autoimmune primary adrenal insufficiency usually affects all three layers of the adrenal cortex, where patients present with deficiencies in cortisol and aldosterone. Isolated hypoaldosteronism has rarely been reported, however because it can cause life-threatening hyponatremia, it is an important entity to recognize. It is important to work up in such patients as they may be in the initial stages of autoimmune Addison’s disease and can progress to developing cortisol deficiency, though the time course to this progression is not well known.