Adrenal adenoma ACTH-secreting

ACTH-dependent Cushing s syndrome is usually caused by overproduction of ACTH by the pituitary gland, causing adrenal hyperplasia (Cushing s disease). Pituitary adenomas account for about 80% of these cases. Ectopic ACTH-secreting tumors and nonneoplastic corticotropin hypersecretion are responsible for the remaining 20% of cases. 

Cushing s disease (caused by a pituitary ACTH-secreting adenoma) or Cushing s syndrome from an adrenal tumour is normally treated by surgical removal of the primary lesion where possible. Cases of ectopic ACTH syndrome associated with carcinoma of the bronchus cannot be treated surgically, and often benefit from medical therapy to control adrenal steroid excess. 

Metyrapone is commonly used in tests of adrenal function. The blood levels of 11-deoxycortisol and the urinary excretion of 17-hydroxycorticoids are measured before and after administration of the compound. Normally, there is a twofold or greater increase in the urinary 17-hydroxycorticoid excretion. A dose of 300-500 mg every 4 hours for six doses is often used, and urine collections are made on the day before and the day after treatment. In patients with Cushing s syndrome, a normal response to metyrapone indicates that the cortisol excess is not the result of a cortisol-secreting adrenal carcinoma or adenoma, since secretion by such tumors produces suppression of ACTH and atrophy of normal adrenal cortex. 

Primary adrenal adenoma (Cushing s syndrome) Pituitary adenoma secreting ACTH (Cushing s disease) Exogenous cortisol therapy Excessive licorice ingestion Bartter s syndrome (defective renal CL reabsorption)... 

This is a condition which results from a pituitary adenoma, occuring after total adrenalectomy for Cushing s disease, due to bilateral adrenal hyperplasia. ACTH and MSH may be secreted in response to increased secretion of CRF by the hypothalamus and this results in skin pigmentation. The increased secretion of CRF may be an attempt to maintain the high levels of cortisol that existed before the operation. 

The low dose dexamethasone suppression test (qv) is an example of such a test. Dexamethasone is a powerful cortisol analogue which is capable of suppressing ACTH production and therefore cortisol secretion. In Cushing s syndrome, however, the cortisol levels do not fall, e.g. due to pituitary disease (when the feedback mechanism is insensitive) or due to adrenal carcinoma or adenoma when cortisol secretion is auto-nonomous. 

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