Cushing's syndrome is a condition caused by chronically elevated levels of cortisol or similar adrenal hormones. This disorder can result from cortisol-secreting tumors in your adrenal glands, from taking prescriptions of cortisol-like hormones -- so-called exogenous hormones -- or from excessive stimulation of your adrenal glands by an overactive pituitary gland. Measurement of other adrenal hormone levels, such as DHEA, can help to sort out whether your adrenal glands, your pituitary or exogenous hormones are at the root of your symptoms.
Signs and Symptoms
Regardless of its underlying origin, cortisol excess causes characteristic signs and symptoms. Cortisol increases the deposition of fat in your abdomen, above your collar bones and over your upper back while simultaneously causing wasting of the muscle tissue in your extremities. This creates a picture of central obesity with a "buffalo hump," which is usually accompanied by weakness, thin skin, poor wound healing, stretch marks and easy bruisability. Long-term consequences of Cushing's syndrome include diabetes, osteoporosis, kidney stones, high blood pressure and mental disturbances.
Pituitary Cushing's
Cushing's disease is a specific type of Cushing's syndrome caused by a pituitary tumor that secretes excessive amounts of adrenocorticotropic hormone, or ACTH. ACTH stimulates the outer layers of your adrenal glands, thereby increasing blood levels of all adrenal hormones to varying degrees. Thus, elevations in multiple hormones, such as cortisol, aldosterone, DHEA and sex hormones, point to pituitary overproduction of ACTH as the cause of Cushing's syndrome. As noted in the February 2003 issue of "Endocrine Journal," serum DHEA levels are significantly higher in pituitary Cushing's than in adrenal Cushing's.
Adrenal Cushing's
Cortisol-secreting adrenal tumors are a relatively common cause of Cushing's syndrome. These usually benign growths are typically composed of a single cell type that produces only cortisol. Thus, you develop all of the signs and symptoms of Cushing's syndrome, but measurement of your blood hormone levels demonstrates elevations of cortisol alone. In fact, other hormones, such as DHEA, may actually be abnormally low, because the excess cortisol produced by your adrenal tumor "shuts off" the production of ACTH from your pituitary. Without ACTH, the normal cells in your adrenal gland stop secreting all other hormones. A similar situation exists in Cushing's syndrome arising from prescription cortisol drugs.
Considerations
Cushing's syndrome is a term used to describe any condition that increases your blood levels of cortisol and cortisol-like hormones. Adrenal tumors and exogenous cortisol -- prescription prednisone, for example -- are common causes. Cushing's disease refers specifically to cases of Cushing's syndrome that are caused by ACTH-secreting tumors in your pituitary gland. Pituitary tumors often cause elevations of DHEA, while adrenal tumors or exogenous cortisol suppress DHEA production and lower its concentrations in your bloodstream.
References
- "The Merck Manual of Diagnosis and Therapy, 18th Edition: Cushing's Syndrome"; Mark H. Beers, M.D., Editor-in-Chief; 2006
- "Endocrine Journal"; Osteoporosis Is More Prevalent in Adrenal than in Pituitary Cushing's Syndrome; N. Ohmori, et al.; February 2003
- "Endocrine Journal"; Serum Levels of Dehydroepiandrosterone Sulfate in Patients with Asymptomatic Cortisol Producing Adrenal Adenoma: Comparison with Adrenal Cushing's Syndrome and Non-functional Adrenal Tumor; H. Morio, et al.; August 1996
