Atypical Carcinoid Tumor of the Mediastinum Presenting as Ectopic Cushing’s Syndrome

Abstract

Introduction: Ectopic Cushing’s syndrome (ECS) refers to Cushing’s syndrome (CS) that results from extra-pituitary secretion of adrenocorticotropic hormone (ACTH). Neuroendocrine tumors (NETs) are a rare cause of ECS, and their presence in the anterior mediastinum only represents 2-4% of all cases. We report a rare case of ECS in a patient with an atypical mediastinal carcinoid tumor. Case Presentation: A 38-year-old male with a history of depression presented with generalized weakness, fatigue, and myalgia for one month. A one-week history of nausea and slight shortness of breath was reported. Physical exam and vital signs were unremarkable. Labs revealed hyperglycemia, hypokalemia, and metabolic alkalosis. A random serum cortisol was 47.7 mcg/dL (normal: 3-21 mcg/dL) and a 24-hour urine free cortisol was 7405 mcg/24 hours (normal: 3.5-45 mcg/24 hours). The morning serum cortisol after 8 mg dexamethasone at midnight, was 58.7 mcg/dL. Serum aldosterone and plasma renin activity were both undetectable. CT of the chest showed an anterior mediastinal mass measuring 9.0 x 10.3 x 6.1 cm accompanied by two large mediastinal lymph nodes. A PET CT confirmed the anterior mediastinal mass, which showed mild heterogeneous uptake and no evidence of metastatic disease. Core biopsy of mediastinal mass showed grade II neuroendocrine tumor/atypical carcinoid. Potassium, Spironolactone, Ketoconazole, and Metyrapone were used to control hypokalemia and hypercortisolemia. Trimethoprim-sulfamethoxazole (TMP-SMX) was started for Pneumocystis pneumonia prophylaxis. The patient underwent complete resection of the anterior mediastinal mass, thymectomy, and mediastinal lymph nodes dissection. Histopathology confirmed an atypical carcinoid in the mediastinal mass with negative margins. The rest of the thymus tissue and lymph nodes were negative for malignancy. ACTH and cortisol levels dropped significantly after surgery and the patient was discharged on oral hydrocortisone and TMP-SMX. At 4 weeks follow-up in the clinic, the patient was feeling much better and reported complete resolution of symptoms. Discussion: ECS caused by an atypical carcinoid tumor is an extremely rare finding. Mediastinal NETs tend to have a poor prognosis due to their metastatic tendency and recurrence rates. Due to limited evidence in the medical literature, there’s much uncertainty and controversy regarding the best treatment of NETs. Standardized guidelines for the management of these atypical tumors are not well established. The primary mode of treatment is surgical resection of the ACTH-secreting tumor. However, in cases of advanced and metastatic tumors, surgical resection might not be sufficient and medical therapy with adrenal enzyme synthesis inhibitors may be needed. The use of neoadjuvant chemotherapy and/or radiotherapy remains unclear.