ODP624 A case of Cushing disease demonstrated rapid deterioration of clinical findings and marked hypercortisolemia

INTRODUCTION: In cases of ACTH-dependent Cushing syndrome, the differentiation between Cushing disease and the ectopic ACTH syndrome (EAS) can sometimes be challenging. Herein we report on a case of Cushing disease who showed clinical features resembled EAS caused by malignant neoplasms and required a detour for the diagnosis. CLINICAL CASE: A 49-year-old Japanese woman presented a rapid exacerbation of muscle weakness of her limbs, leg edema and moon face from two months ago. She did not have any past medical history, hypertension, diabetes mellitus, or osteoporosis. Her serum K was 2.6 mEq/L, ACTH level was 151 pg/mL, serum cortisol level was 36.6 μg/dL, and urinary free cortisol (UFC) level was 4250 μg/day. Serum cortisol after 1 mg dexamethasone suppression test (DST) showed 41.9 μg/dL and that after 8 mg DST was 14.1 μg/dL. A pituitary MRI demonstrated a poor enhancement area with a clear margin of 10 mm in diameter in her dorsal side of the pituitary gland. She was diagnosed with ACTH-dependent Cushing syndrome and metyrapone was initiated. Soon she developed severe cough with infiltrative shadows on her lungs two days later. Her respiratory condition deteriorated rapidly, and she was urgently transferred to our hospital and intubated one week later. She had complicated pneumocystis carinii, nocardia pneumonia, and severe respiratory failure based on immunodeficiency due to hypercortisolemia. She was treated with systemic management in the intensive care unit, infection treatment and dose adjustment of metyrapone. Her condition improved and she was extubated on the 8th day. Although she had the pituitary tumor, EAS caused by a malignant neoplasm was suspected because of a combination of rapid clinical deterioration, marked hypercortisolemia and hypokalemia. However gastrointestinal tract survey, 18F-PET/CT and somatostatin receptor scintigraphy did not show any significant lesions. Finally, selective inferior petrosal sinus sampling (IPSS) demonstrated over secretion of ACTH from the pituitary gland. ACTH decreased to an undetectable level and hydrocortisone was supplemented after transsphenoidal surgery. No recurrence was observed in 1 year of follow-up. Pathological findings showed a densely granulated type of ACTH-producing adenoma without Crooke's change. KI-67 index were 4.7%, which was higher than that in general ACTH producing pituitary adenomas. CONCLUSION: We experienced Cushing disease with the rare clinical course. This case suggests that although a step-by-step approach is often adopted to make a differential diagnosis of patients with ACTH-dependent Cushing's syndrome, ultimately IPSS is required. Because her KI-67 index showed 3 or higher despite the gentle tumor behavior, careful follow-up is required. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.