[Ectopic Adrenocorticotropic Hormone-producing Pulmonary Carcinoid Tumor Presenting as Cushing Syndrome].

The patient was a 57-year-old female who felt muscle weakness and visited a physician. Hypokalemia was pointed out, and she was referred to our hospital for detailed examination and treatment. Hormone-related tests and imaging were performed, and the patient was diagnosed as Cushing syndrome. Moreover, an ectopic adrenocorticotropic hormone (ACTH)-producing tumor was suspected. The whole body was examined to find a tumor, but no apparent lesion was found, except for a small nodule of 5-mm in size was present in the right middle pulmonary lobe on chest computed tomography (CT). It was decided to perform surgical resection for both diagnosis and treatment. Pathological diagnosis was a typical carcinoid. On immunostaining, ACTH-positive cells were detected, and the lesion was definitely diagnosed as an ectopic ACTH-producing tumor. Since the ACTH level after surgery returned to normal, the lesion was concluded to be completely excised.