MON-905 A Case of Cushing’s Disease with Glucocorticoid Positive-Feedback

Background: Although paradoxical response of cortisol (F) during high dose dexamethasone (Dex) suppression test (DST) is observed in a part of ectopic ACTH syndrome, few reports have been shown in Cushing’s disease (CD). It suggests a presence of glucocorticoid (GC)-driven positive-feedback loop. However, the underlying mechanism remains elusive. Here we present a case of CD showing clear clinical and pathophysiological evidences of GC positive-feedback using ex vivo 3-dimensional (D) culture method. Case: A 62-year-old woman manifested typical Cushing’s symptoms, including moon face, central obesity, hypertension, hypokalemia, and vertebral fractures. Endocrinological data were consistent with a diagnosis of CD; morning plasma ACTH 299 pg/mL, serum F 28 μg/dL, midnight serum F 43 μg/dL, and 24hr urinary free cortisol 988 μg/day. CRH test showed a slight increase in plasma ACTH levels (1.4 fold), and pituitary MRI revealed a 14 mm macroadenoma invading into the left cavernous sinus. Interestingly, both 1 mg and 8 mg DST showed a paradoxical increase in serum cortisol levels (27.7→64.7μg/dL and 17.17→35.68μg/dL, respectively). These data indicated a presence of positive-feedback response to GC in the tumor. Indeed, after the initiation of metyrapone (1,000 mg/day) administration for the treatment of hypercortisolemia, plasma ACTH levels were decreased to 147.5 pg/mL accompanied with the decrease in serum F levels to 4.12 μg/dL. Moreover, pituitary tumor obviously shrank during the metyrapone treatment. Thereafter, we undertook transsphenoidal surgery and plasma ACTH and serum F levels decreased to 35.8 pg/mL and 7.6μg/dL, respectively. ex vivo studies: To prove the presence of the positive feedback response and explore the underlying mechanisms, we performed a primary culture experiment using the tumor and applied 3D culture method. The resected tumor tissue was enzymatically digested, dispersed and embedded into the Matrigel. Then cells were treated with Dex (0.1-10 nM), and ACTH concentrations were measured after 72 hrs. Interestingly, ACTH levels significantly increased by 10 nM Dex treatment at 72 h (129 %, p <0.01), indicating a paradoxical response to Dex in the tumor ex vivo. Conclusions: To our knowledge, this is the first case of CD who showed clinically obvious GC positive-feedback that was proved by ex vivo 3D primary culture cell models. Notably, tumor shrinkage was observed during the metyrapone treatment, suggesting that GC positive-feedback mechanisms also involve tumor proliferation. Further investigation is required for elucidating the underlying mechanisms.