THU015 Unilateral Adrenal Hyperplasia Causing ACTH-independent Hypercortisolism

Disclosure: N. Mogar: None. M.A. McConnell : None. R. Yu: None. J.E. Weinreb: None. Background: Adrenal cortical hyperplasia is defined radiographically as a non-malignant growth or enlargement of the adrenal glands. Adrenal hyperplasia is most commonly bilateral, with unilateral adrenal hyperplasia occurring less frequently. Unilateral adrenal hyperplasia has been associated with primary hyperaldosteronism, and there are only a few case reports describing unilateral adrenal hyperplasia associated with ACTH-independent hypercortisolism. Clinical Case: A 56-year-old man with sleep apnea was incidentally found to have a 4.6 cm left adrenal nodule found on computed tomography (CT) chest imaging. Adrenal CT revealed a heterogeneous 4.6 x 3.3 x3.7 cm left adrenal mass with internal calcifications and a portion of the mass measuring 38 Houndsfield units (HU). His 8AM serum cortisol level was 19.80 mcg/dL (5-23 mcg/dL). No ACTH level was collected; however, a serum DHEA-S level was 55 mcg/dL (32-240 mcg/dL). After low dose dexamethasone suppression test (LDDS), the serum cortisol level was elevated at 2.3 mcg/dL (<1.8 mcg/dL). Repeat LDDS revealed a cortisol level of 2.9 mcg/dL. A 24-hour urine free cortisol level was 27.2 mcg/24h (4-50 mcg/24h). Testing for pheochromocytoma and hyperaldosteronism was negative. The patient had no historical or physical signs of Cushing’s syndrome and no signs of malignancy. Due to concerning features on adrenal CT imaging (tumor size >4 cm, internal calcifications, and HU >10), the patient underwent unilateral adrenalectomy. The patient did not receive intraoperative corticosteroids and remained normotensive post-operatively. However, his post-operative 8AM cortisol level was <0.2 mcg/dL (5-23 mcg/dL) on two separate occasions. He was discharged on a short course of hydrocortisone, with eventual recovery of his hypothalamic-pituitary-adrenal (HPA) axis. Pathology revealed a diagnosis of cortical adrenal hyperplasia. Conclusion: The presence of postoperative hypocortisolemia demonstrates that this patient had ACTH-independent hypercortisolism. This case report would be one of few describing the rare diagnosis of unilateral adrenal hyperplasia associated with ACTH-independent hypercortisolism and would add to the sparse literature currently available on this condition. Additionally, this case report highlights the clinical significance of mild autonomous cortisol secretion (MACS); despite only having an unsuppressed cortisol level following LDDS, this patient was found to have a suppressed HPA axis after unilateral adrenalectomy requiring corticosteroids. Early identification and treatment of MACS and treatment of adrenal insufficiency following adrenalectomy is essential to prevent adverse events. Presentation: Thursday, June 15, 2023