Difficult Locating Diagnosis in a Case of Cushing's Syndrome Due to Bronchial Carcinoid: Case Report and Literature Review

  Objective  To explore the localization diagnosis method of Cushing's syndrome caused by ectopic adrenocorticotropic hormone (ACTH) syndrome due to bronchial carcinoid.

  Methods  Based on the clinical data, we retrospectively analyzed the process and method of localization diagnosis in a 49-year-old female patient with Cushing's syndrome which was difficult to localize the etiology.

  Results  The patient had been misdiagnosed as Cushing's disease, for which she had accepted transsphenoidal pituitary surgery. The symptoms of Cushing's syndrome persisted after the pituitary surgery. After six months' follow-up and treatment with ketoconazole for several weeks, chest CT revealed that the size of one small nodule(about 5 mm in diameter) in the right lung didn't change for 9 months. The somatostatin receptor scintigraphy and fluorodeoxyglucose-positron emission tomography (FDG-PET) could not confirm that the pulmonary nodule was the tumor producing ACTH. The results of inferior petrosal sinus sampling confirmed that the etiology was ectopic ACTH syndrome. After removing the right middle lobe of the lung through thoracoscopic surgery, plasma ACTH, serum cortisol, and 24-hour urinary free cortisol were reduced to normal. The nodule was histologically diagnosed as a typical bronchial carcinoid containing immune-reactive ACTH as shown in immunohistochemical staining.

  Conclusions  Inferior petrosal sinus sampling may be important for localizing the lesion of ectopic ACTH production, which, combined with different imaging techniques, should be considered in patients suspected for ectopic ACTH syndrome. Exploratory surgery may be sometimes needed.