Cushing Syndrome

Topics: Cortisol, Hypothalamus, Endocrine system Pages: 5 (1456 words) Published: March 20, 2013
Cushing Syndrome

‡ Sometimes called hypercortisolism. ‡ Cushing s syndrome is a hormonal disorder caused by prolonged exposure of the body s tissues to high levels of the hormone cortisol. Causes
Pituitary Adenoma ‡ Pituitary adenomas cause 70 percent of Cushing s syndrome cases, excluding those caused by glucocorticoid use. These benign, or noncancerous, tumors of the pituitary gland secrete extra ACTH. Most people with the disorder have a single adenoma. Ectopic ACTH Syndrome ‡ Some benign or, more often, cancerous tumors that arise outside the pituitary can produce ACTH. This condition is known as ectopic ACTH syndrome. Adrenal Tumors ‡ In rare cases, an abnormality of the adrenal glands, most often an adrenal tumor, causes Cushing s syndrome. Most of these cases involve noncancerous tumors of adrenal tissue called adrenal adenomas, which release excess cortisol into the blood. Familial Cushing s Syndrome ‡ Most cases of Cushing s syndrome are not inherited. Rarely, however, Cushing s syndrome results from an inherited tendency to develop tumors of one or more endocrine glands. * Prolonged use of glucocorticoids

* Pituitary Adenoma
* Ectopic ACTH Syndrome
* Adrenal Tumors
* Familial Cushing’s Syndrome

Stimulate hypothalamus to release Corticotropin releasing hormone (CRH) ↓
Anterior Pituitary Gland secretes adrenocorticotropin hormone (ACTH) ↓ Through blood stream
Stimulates Adrenal Cortex to release cortisol
↓ Due to disrupted feedback loop of cortisol ↑Release of cortisol
Tests to Diagnose Cushing s Syndrome
24-hour urinary free cortisol level. ‡ In this test, a person s urine is collected several times over a 24-hour period and tested for cortisol. Levels higher than 50 to 100 micrograms a day for an adult suggest Cushing s syndrome. The normal upper limit varies in different laboratories, depending on which measurement technique is used Midnight plasma cortisol and late-night salivary cortisol measurements ‡ The midnight plasma cortisol test measures cortisol concentrations in the blood. Cortisol production is normally suppressed at night, but in Cushing s syndrome, this suppression doesn t occur. If the cortisol level is more than 50 nanomoles per liter (nmol/L), Cushing s syndrome is suspected. The test generally requires a 48-hour hospital stay to avoid falsely elevated cortisol levels due to stress. ‡ However, a late-night or bedtime saliva sample can be obtained at home, then tested to determine the cortisol level. Diagnostic ranges vary, depending on the measurement technique used Low-dose dexamethasone suppression test (LDDST) ‡ In the LDDST, a person is given a low dose of dexamethasone, a synthetic glucocorticoid, by mouth every 6 hours for 2 days. Urine is collected before dexamethasone is administered and several times on each day of the test. A modified LDDST uses a onetime overnight dose. Dexamethasone-corticotropin-releasing hormone (CRH) test. ‡ This test combines the LDDST and a CRH stimulation test. In the CRH stimulation test, an injection of CRH causes the pituitary to secrete ACTH. Pretreatment with dexamethasone prevents CRH from causing an increase in cortisol Tests to Find the Cause of Cushing s Syndrome

CRH stimulation test. ‡ As a result of the CRH injection, people with pituitary adenomas usually experience a rise in blood levels of ACTH and cortisol because CRH acts directly on the pituitary. This response is rarely seen in people with ectopic ACTH syndrome and practically never in those with adrenal tumors. High-dose dexamethasone suppression test (HDDST) ‡ The HDDST is the same as the LDDST, except it uses higher doses of dexamethasone. This test helps separate people with excess production of...
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