A reappraisal of the utility of somatostatin receptor scintigraphy in patients with ectopic adrenocorticotropin Cushing's syndrome

Ectopic ACTH hypersecretion is a rare cause of Cushing's syndrome. Bronchial carcinoids are the most common neoplasms causing the occult ectopic ACTH syndrome (EAS). Localization of these tumors is often difficult. The diagnostic utility of somatostatin receptor scintigraphy (SRS) in EAS has been studied in a limited number of patients with conflicting results. Herein we report our experience with 12 consecutive cases. Histological confirmation was obtained in nine patients, the majority being bronchial carcinoids. Among the seven patients with histologically confirmed bronchial carcinoids, SRS was performed in six patients. In three patients SRS correctly localized a bronchial carcinoid tumor at presentation. In the remaining three it became positive after 8, 22, and 27 months during follow-up. In two patients SRS was positive without any finding in the corresponding conventional imaging study. In two patients positive computed tomography/ magnetic resonance imaging preceded SRS localization. There was no false positive SRS. Among three patients with highly suspected EAS, SRS was positive in one. Both patients with EAS due to medullary thyroid carcinoma had focal positive uptake. In summary, in this study a substantial number of patients had positive tumor localization by SRS. Therefore, SRS is a useful tool in the evaluation of patients with EAS.