Most patients with adrenocorticotropin-de-pendent Cushing's syndrome prove to have discrete corticotroph adenomas on pathologic examination. Occasionally, however, such patients will have corticotroph hyperplasia with no signs of a coexisting adenoma. In most large surgical series, the incidence of corticotroph hyperplasia in Cushing's Syndrome is between 1 and 10%. Most Patients present with clinical and laboratory findings similar to those in patients with corticotroph adenomas, although some have marked elevations in urinary cortisol levels and/or lack of response to high-dose dexamethasone. In the few cases that include treatment results, hypophysectomy appears to lead to clinical remissions, although long-term follow-up is not available for most cases. At least some cases of Cushing's syndrome and corticotroph hyperplasia are secondary to ectopic corticotropin-releasing hormone (CRH) production. Although such tumors can be cliniclly evident on presentation, they can also be occult, leading to pitutary exploration for presumed corticotroph adenomas. Therefore, serum CRH levels should be measured in patients with Cushing's syndrome and corticotroph hyperplasia. If these levels are elevated, a careful search should be performed for possible ectopic sources of CRH.
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