MON-330 Cushing Syndrome Secondary to Neuroendocrine Lung Carcinoma: To X-Ray or Not to X-Ray?

Introduction Adrenocorticotropic hormone (ACTH) overproduction leads to hypercortisolism and Cushing syndrome (CS). We describe a rare case of ectopic ACTH secretion (EAS) secondary to a primary lung neuroendocrine tumor (NET). Case description A 30-year-old female presented with fatigue, muscle weakness and poor memory. She had associated weight gain, hair loss and amenorrhea. She had a history of recent microprolactinoma treated with Cabergoline. Vital signs were normal aside from mild hypertension. Physical examination revealed facial acne, posterior neck fullness, hirsutism and abdominal striae. Morning cortisol was 53.6 (4.3-22.4mcg/dl) and ACTH was 147 (0-46pg/ml). A midnight salivary cortisol level was 2.54 (<0.09mcg/dL), urine 24-hour cortisol was 4405 (4-55mcg/24h) and potassium was 3.3 (3.5-4.5mmol/L). Her glycosylated hemoglobin was 6.4% and insulin like growth factor was 163 (53-331 ng/ml). A low-dose 1mg and a high-dose 8mg dexamethasone suppression test failed to suppress cortisol confirming EAS. A review of brain magnetic resonance imaging (MRI) from Vietnam at the time of diagnosis and post treatment did not reveal a microprolactinoma indicating possible misdiagnosis. Given the high clinical suspicion for EAS, a chest x-ray was obtained first which identified two left upper lobe lung masses. As such, inferior petrosal sinus sampling (IPSS) was avoided. A computed tomography guided lung biopsy confirmed well-differentiated NET, staining positive for synaptophysin, chromogranin and pancytokeratin. The Ki-67 proliferation index was low <2%. Positron emission tomography showed hypermetabolic activity within the lung masses, left hilum and mediastinal lymph nodes. Octreotide scan showed increased radiotracer uptake within the lung masses and corresponding lymph nodes. She underwent wedge resection of her left upper lobe and was treated with a steroid taper perioperatively. She required intermittent insulin therapy for hyperglycemia. Post-operatively, her ACTH, blood glucose and cortisol normalized. She remains asymptomatic at 6-month follow up. Conclusion ACTH-producing pituitary adenomas result in most cases of ACTH-dependent CS and 10-15% result from EAS. EAS must be suspected if a pituitary adenoma is not visible on MRI. Challengingly, up to 40% of ACTH-dependent CS from a pituitary source may not have a visualizable adenoma and IPSS is invasive. Although bronchopulmonary NETs are usually non-functional and 1-2% cause CS, studies have shown that pulmonary NETs are up to 4cm in size. As such, we began with a simple chest-xray looking for an ectopic source rather than subjecting our patient to IPSS as guidelines suggest. Hypokalemia can be a clue to EAS causing mineralocorticoid receptor activation. Our diagnosis was made and fortunately a well-differentiated localized tumor with low Ki-67 mitotic index yielded the positive outcome seen in our patient.