The Cushing syndrome induced by bronchial carcinoid tumors

To define the clinical spectrum of bronchial carcinoid tumors in patients presenting with the Cushing syndrome, to evaluate the role of chest radiographs and computed tomography in their diagnosis, to review the characteristic histologic features, and to determine patient outcome.

Retrospective analysis of consecutive patients.

A referral-based medical center.

Fifteen consecutive patients with the Cushing syndrome evaluated at the Mayo Clinic with histologically proven bronchial carcinoid tumors.

Clinical, radiographic, and histologic features.

The Cushing syndrome was the initial clinical presentation, and bronchial carcinoid tumors were found later in all 15 patients. The diagnosis of carcinoid tumor was proved histologically in all cases. Ten biopsies showed typical carcinoid tumors, three were histologically atypical, and three were metastatic. Corticotropin was detected by immunostaining in seven of these tumors. Biochemical analysis showed marked elevations of circulating corticotropin with a mean serum value of 156 +/- 58 pmol/L (normal, 4 to 22 pmol/L). Additional clinical features included hypokalemia in six patients and glucocorticoid response to either high-dose dexamethasone or metyrapone in 6 of 13. These hormonally active carcinoid tumors were frequently radiographically occult, with 10 of 15 patients initially having normal chest radiographs. Computed tomography was successful in locating carcinoid tumors in five patients with negative chest radiographs evaluated after 1980. All five remaining patients with normal chest radiographs evaluated before 1980 eventually developed nodular lesions on standard chest radiography from 1 to 10 years later. Ten patients achieved complete remission and two patients, partial remission of the Cushing syndrome after surgical resection. Three patients continued to have symptomatic glucocorticoid excess due to metastatic disease.

Although uncommon, the Cushing syndrome may be the initial clinical manifestation of an otherwise indolent bronchial carcinoid tumor. Radiographic imaging of occult lesions can be successfully accomplished with computed tomography. Surgical resection is curative in most patients with this disorder.