Endocrine Abstracts

JOINT1536

Introduction: Ectopic Cushing’s syndrome (ECS) accounts for 15% of all endogenous Cushing’s syndromes and 10-20% of ACTH-dependent Cushing’s syndromes. Medullary thyroid carcinoma (MTC) is a rare cause of ectopic ACTH secretion in patients with ACTH-dependent Cushing’s syndrome, described in less than 1% of MTC cases.

Summary: We present the case of a 68-year-old patient with pronounced hypokalemia and weakness, initially attributed to hypercortisolemia due to Cushing’s syndrome (previously diagnosed as an adrenal incidentaloma). Based on very high basal and suppressed ACTH levels and high basal calcitonin value of 2239. 00 pg/mL, ectopic secretion of ACTH was supposed and neck and chest imaging was performed. The imaging revealed a multinodular goiter with cervical lymphadenopathy and neoplastic change in the left lung. Additionally, a percutaneous lung biopsy of the detected lung tumor confirmed the suspicion of metastatic MTC. In preoperative treatment, severe hypokalemia was corrected with high doses of potassium administered both orally and parenterally until the introduction of ketoconazole (200 mg three times daily). Ketoconazole reduced cortisol levels, and hypokalemia was corrected without evidence of hepatotoxicity. A PET/CT scan using 18F-FDG showed moderately increased accumulation of 18F-FDG (SUV max 1. 7) in nodules in the right thyroid lobe (21 mm in diameter), with further intensification of 18F-FDG uptake (SUV max 2. 1) in the upper lobe of the left lung at the junction of S3 and S4. The patient underwent combined surgery, including a total thyroidectomy and atypical resection of the upper lobe of the left lung (OPIII U-VATS). Postoperatively, ketoconazole was discontinued, and cortisol levels remained normal. Serum potassium levels normalized without the need for potassium replacement therapy.

Conclusion: The expected therapeutic effect of the surgery was achieved in terms of the prompt resolution of ectopic ACTH secretion from the metastatic medullary carcinoma and the control of hypercortisolism effects, which were life-threatening for the patient. Postoperatively, ketoconazole was discontinued, while maintaining normal cortisol levels and serum potassium values without the need for potassium supplementation. Monitoring of calcitonin levels continues, with an assessment for the potential use of targeted therapy with tyrosine kinase inhibitors.