A case of ectopic ACTH syndrome: diagnostic difficulties caused by intermittent hormone secretion

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Abstract
A patient with a thymic carcinoid tumor causing ectopic ACTH syndrome is presented. The case illustrates the rapid development of the clinical and laboratory findings often associated with ectopic secretion of ACTH, including severe proximal myopathy, emotional lability, and hypokalemic alkalosis. Interpretation of conventional tests of pituitary-adrenal function was complicated by intermittent secretion of ACTH by the tumor. The results of selective venous sampling for ACTH ruled out pituitary ACTH hypersecretion and were suggestive of a thymic source; computerized tomography of the chest localized the tumor. In vivo and in vitro investigations confirmed excessive ACTH production by the tumor, and surgical resection plus radiotherapy has resulted in resolution of the syndrome. The diagnostic problems created by intermittent secretion of ACTH by these tumors and the pre-operative and post-operative medical management of these patients are discussed.