Localization of ectopic cyclic Cushing's syndrome, which causes life-threatening complications, is challenging. A 70-year-old woman showed cyclic hypokalemia and hyperglycemia and was diagnosed with cyclic ectopic Cushing's syndrome. Although somatostatin-receptor scintigraphy failed to localize the responsible tumor, fluorodeoxyglucose-positron emission tomography (FDG-PET) showed the uptake of tracer in a lung tumor. Lobectomy resulted in remission. The resected adrenocorticotropic hormone (ACTH)-producing neuroendocrine tumor had Ki-67<2% and negative staining for somatostatin receptors. This is the first case assessed both radiological findings and pathological findings in cyclic ectopic Cushing's syndrome. Subsequent FDG-PET is recommended if somatostatin-receptor scintigraphy is negative.
Keywords: ACTH-producing tumor; FDG-PET; cyclic; somatostatin-receptor.