Relationship between adrenal cortex pathology in Cushing's syndrome and its response to the dexamethasone suppression test.

Cushing's syndrome is a severely disabling condition which can cause death if left untreated. Endogenous Cushing's syndrome can be ACTH-dependent or ACTH-independent. The ACTH-dependent type is more common and is usually caused by diffuse hyperplasia on the adrenal cortex. This study investigated the response to low- and high-dose dexamethasone suppression testing of 30 adrenalectomized patients with Cushing's syndrome, average age 37.3 +/- 9.7 years. Twenty-four (79.3%) patients were female, and six (20.7%) were male. Bilateral adrenalectomy was performed in 14 (48.2%) patients and unilateral adrenalectomy (nine and seven right adrenalectomy) in 16 (51.8%). Two of the bilateral adrenalectomies were applied via endoscopic surgical approach. In the histopathological evaluation, diffuse hyperplasia was diagnosed in 13 (44.8%) patients and nodular hyperplasia in eight (26.6%), three macronodular and five micronodular hyperplasia. Adrenal cell adenoma was diagnosed in nine (28.6%) patients. Classic dexamethasone suppression testing was performed on all patients. Plasma levels of cortisol were not significantly decreased after low-dose testing, but plasma levels of cortisol were significantly decreased after high-dose testing in the diffuse hyperplasia group. In summary, due to the pathological changes of the adrenal cortex, dexamethasone suppression testing can differentiate between the two types of Cushing's syndrome.