Thallium-201 Scintigraphy Was Useful in Diagnosing Ectopic ACTH Syndrome Due to Bronchial Carcinoid

Initial investigations of a 70-year-old woman with clinical Cushing's syndrome, including overnight dexamethasone suppression test, CRH test, and pituitary MRI, suggested the presence of ectopic ACTH production. Thoracic computed tomography (CT) scan revealed a mass measuring 7mm in the right lung, but it was thought to be an incidental opacity, leaving the source of ectopic ACTH undetermined for several years. During this period, although the size of the lung opacity did not change remarkably, serum cortisol levels became elevated to 43μg/dl, and the patient's symptoms worsened. T1-201 SPECT demonstrated intense accumulation in the right lung. The mass was surgically resected using thoracoscopy to investigate it as the focus of ACTH production. Histological and immunohistochemical examination confirmed that the area of intense T1-201 uptake was an ACTH-producing bronchial carcinoid. Plasma ACTH and cortisol levels decreased immediately after the surgery. In conclusion, this case demonstrated T1-201 scintigraphy as a useful tool in identifying the location of an ACTH-producing bronchial carcinoid.