The Search for Occult Ectopic Acth-producing Tumors

Cushing's syndrome due to an autonomously functioning adrenal adenoma or to an ACTH-secreting pituitary adenoma can be confidently diagnosed, especially with recent advances in cross-sectional imaging (CT of adrenal, MRI of pituitary) and biochemical testing (IRMA ACTH assay, petrosal sinus sampling, CRH test). The occult ectopic ACTH syndrome remains the major unsolved clinical problem in Cushing's syndrome. Review of 40 cases seen at the NIH and the world literature reveals that occult bronchial carcinoid tumors are the responsible tumor in over half the cases. These tumors are often confused with “pituitary” Cushing's syndrome by classic endocrinologic studies. A diagnostic algorithm is suggested, emphasizing the value of magnetic resonance imaging for detecting small central bronchial carcinoid tumors.