MON-409 Ectopic ACTH Syndrome with a Pituitary Mass

Background: The ectopic ACTH syndrome comprises 10% of Cushing’s syndrome cases. It is associated with an array of both highly malignant and more indolent tumors. Clinical features develop rapidly in ectopic ACTH syndrome. Distinguishing ectopic ACTH production from pituitary ACTH secretion is essential in determining appropriate management and may be challenging in the case of an occult neuroendocrine tumor. Clinical Case: A 46 year-old male presented to the ER after his PCP identified hypokalemia to 1.6 mmol/L (3.5- 5.0 mmol/L). He endorsed two weeks of proximal muscle weakness, lower extremity edema, a retro-orbital headache, and 10lb weight loss. Exam revealed mild facial fullness and pitting edema to the knees. No supraclavicular or dorsal cervical adiposity, violaceous abdominal striae or hyperpigmentation was observed. His blood pressure was elevated at 177/92 and an EKG revealed sinus bradycardia at a rate of 44 bpm. An 8AM cortisol was elevated at 67.4 mcg/dL (2.5-19.5 mcg/dL). ICU admission for blood pressure control and IV potassium supplementation was required. There was concern for Cushing’s disease given an inappropriately elevated ACTH level of 159.3 pg/mL (6-50 pg/mL). However, ectopic ACTH was highly suspected given the rapid development of symptoms and a smoking history of roughly 60 pack yrs. A CT of the chest, abdomen, and pelvis revealed no findings suspicious for malignancy. An MRI brain revealed a 19mm sellar and suprasellar mass atop the pituitary extending superiorly in the supra-diaphragmatic region adjacent to the pituitary stalk with a thickened, enhancing infundibulum. The patient required 60meq TID of oral KCl at discharge. Insulin dependent DMII rapidly developed in the weeks following discharge. An 8mg dexamethasone suppression test was performed with a baseline 8AM cortisol of 88 mcg/dL. Post dexamethasone, 8AM cortisol was 62 mcg/dL. Although these results were not consistent with the 50% reduction in cortisol levels expected by a pituitary adenoma in response to high dose dexamethasone administration, a trans-sphenoidal hypophysectomy was undertaken per patient preference. A pale discohesive tissue was identified intra-operatively which stained for ACTH, consistent with a corticotroph macroadenoma. An Indium-111 pentetreotide scan was negative for evidence of a somatostatin receptor expressing neoplasm. Two months after surgery, early-afternoon cortisol decreased to 7.5 mcg/dL. The patient’s insulin dependence gradually resolved as did his hypokalemia, edema, weakness, and weight loss. Conclusion: We describe an unusual case wherein clinical features of the ectopic ACTH syndrome developed over the course of two weeks in a lifelong smoker. Despite failing an 8mg dexamethasone test, a corticotroph macroadenoma was discovered. There was no identifiable source of ectopic ACTH on an octreotide scan despite a highly suggestible presentation.