A Challenging Case of Cushing's Syndrome Due to Ectopic Hormone Secretion

Adrenocorticotropic hormone (ACTH)-dependent Cushing's syn-drome secondary to an ectopic source is an uncommon condition. Hypercortisolism due to ectopic ACTH syndrome is usually rapidly progressive, and excess cortisol levels can lead to severe clinical manifestations, potentially life-threatening. We present the case of a 67-year-old woman who presented to the endocrinological evalu-ation for severe hypokalemia and massive edema of the upper and lower limbs. Hormonal investigations showed elevated plasma total cortisol, 24-h urinary free cortisol, and unsuppressed cortisol fol-lowing 1 mg and 8 mg dexamethasone suppression test, high level of ACTH suggestive for ACTH-dependent Cushing's syndrome. Calcitonin and chromogranin A levels were also elevated. Head magnetic resonance imaging (MRI) evaluation revealed a pitui-tary microadenoma. However, in the context of the onset of severe symptoms in the short term and the association of chronic hypoka-lemia with the failure of plasma cortisol suppression and the very high value of ACTH, a Cushing's syndrome with ectopic secretion of ACTH was suspected. Neck and abdomen computed tomogra-phy (CT) scan showed a heterogeneous nodular mass of 14 x 13 mm in size with macrocalcifications in the right thyroid lobe and bilateral adrenal enlargement, confirming the diagnosis of ectopic ACTH syndrome, with thyroid nodule being the likely source of ectopic ACTH secretion. Due to hypokalemia refractory to treat-ment, severe hypercortisolism in the conditions of unavailability of steroidogenesis inhibitors, emergency bilateral adrenalectomy was performed. Diagnosis of ectopic ACTH syndrome is challenging and requires a multidisciplinary approach. Thyroid evaluation is im-portant to identify a possible source of ectopic secretion of ACTH in the context of medullary thyroid carcinoma (MTC).