6853 A Curious Case of MACS

Abstract Disclosure: M. Dillon: None. A. Syeda: None. V. Kantorovich: None. Introduction: Mild autonomous cortisol secretion (MACS) is characterized by biochemical evidence of mild hypercortisolemia inducing metabolic comorbidities without any obvious phenotypic stigmata of Cushing’s syndrome (CS). This case highlights the challenges faced in the diagnosis and management of MACS. Case: A 76-year-old female with past medical history of class II obesity (BMI 31.83 kg/m2), type 2 diabetes mellitus, hypertension, hyperlipidemia, osteoporosis and chronic kidney disease stage IIIb was diagnosed with MACS after an overnight 1 mg dexamethasone suppression test (DST) showed unsuppressed 8 AM cortisol of 2.4 mcg/dL (<1.8 mcg/dL). Dexamethasone level was appropriate at 355 ng/dL (180-550 ng/dL), ACTH was <5 pg/mL (6-50 pg/mL) and DHEA-S was normal. Late night salivary cortisol (LNSC) levels were elevated to 0.12 mcg/dL (< 0.09 mcg/dL). The 24-hour urine cortisol level was normal. Baseline 8 AM cortisol level was 17 mcg/dL and ACTH was 19 pg/mL. Abdominal CT scan showed a 1 cm left adrenal nodule of 25 HU density and a normal right adrenal with no atrophy. Phaeochromocytoma and primary hyperaldosteronism work up was negative. She started on Mifepristone 300 mg daily and titrated up to 600 mg daily. She presented to our institution one month later with 1 week of nausea, vomiting and muscle weakness. Laboratory studies revealed acute kidney injury with creatinine of 6.69 mg/dL (baseline Cr 1.5 mg/dL) and rhabdomyolysis with creatinine kinase level of 12,819 U/L (24-173 U/L) and urine myoglobin level of 888 ng/mL (0-13 ng/mL). It was evident that her catastrophic presentation was from development of adrenal insufficiency in the setting of Mifepristone glucocorticoid receptor blockade. The drug was discontinued immediately. She was treated with intravenous hydration and intermittent diuretics. Over 10 days, her clinical status gradually improved and creatinine decreased to baseline levels. Discussion: MACS is a challenging diagnosis as cortisol levels are affected by several variables including obesity, drugs, and poorly controlled diabetes. Hence, a meticulous evaluation is mandated before confirming the diagnosis. Our patient’s baseline cortisol and ACTH levels were normal, and her DST and LNSC levels were mildly elevated. Unilateral cortisol producing adenoma causes contralateral gland atrophy due to suppressed ACTH. This was not evident in our patient, thus making the diagnosis questionable. Adrenalectomy is the treatment of choice in MACS with adrenal adenoma. Off label medical management with Mifepristone, a glucocorticoid receptor antagonist, is being pursued in select cases and was trialed due to our patient's age and surgical risk. Mifepristone is approved for the treatment of hyperglycemia due to CS. The data supporting its use in MACS is sparse. Therefore, it is important to be aware of associated risks of Mifepristone when advising patients. Presentation: 6/3/2024