Cushing's disease is a metabolic disorder that affects the adrenal glands. The adrenal glands produce several different hormones including adrenaline, corticosterone, aldosterone and hydrocortisone (also known as cortisol). In Cushing's, the adrenal glands over-produce the hormone cortisol.
What is Cortisol?
Cortisol is responsible for regulating blood pressure, glucose metabolism, immune function, insulin release and inflammatory response. It's also knows as the "Stress Hormone" because it controls the body's "fight or flight" response to stress.
In normal people, cortisone levels are higher in the morning and lower by the end of the day. In people with Cushing's disease and Cushing's syndrome, the levels remain unnaturally high throughout the day.
Causes
Cushing's syndrome and Cushing's disease are two separate disorders. Both involve an increase of cortisol in the body, but each has different causes.
Cushing's syndrome is usually the symptom of another disease or disorder. The most common causes of Cushing's syndrome are the long-term use of oral steroid medications, like Prednisone, and Cushing's disease. Cancers or growths on the adrenal glands are another, less common, cause of Cushing's syndrome.
Cushing's disease is usually caused by a tumor on the pituitary gland, which controls the adrenals' production of cortisol. As the pituitary tumor grows, it irritates the gland causing it to release more of the hormone that stimulates the adrenal glands. Most pituitary tumors are non-cancerous but they can cause blindness if they become too large.
Symptoms
The most common symptom of Cushing's syndrome is the collection of fat deposits in the torso, upper back, neck and face. This often results in a rounded, or moon-shaped, face and the appearance of a "buffalo hump" on the upper back. Other symptoms include muscle weakness, fatigue, thin, easily-bruised skin, irregular menstrual periods, elevated blood sugar, bone loss and depression. Some of the symptoms mimic other disorders, which makes Cushing's disease and syndrome difficult to diagnose.
Diagnosis
Several tests exist to diagnose both Cushing's Disease and Cushing's Syndrome and often several tests are needed to get a definitive diagnosis. The three most common tests are; the 24-hour Free Urinary Cortisol Test, the Midnight Plasma Cortisol and Late-Night Salivary Cortisol Test, and the Low-Dose Dexamethasone Suppression Test (LDDST).
The 24-Hour Free Urinary Cortisol Test measures the urinary levels of cortisol over a 24-hour period. Several collections are taken during that period and levels higher than 50 to 100 micrograms per day may indicate Cushing's. However, different labs may use different testing methods so results may vary.
The Midnight Plasma Cortisol and Late-Night Salivary Cortisol Test measures blood cortisol. Cortisol levels are usually lower at night so a reading of more than 50 nanomoles per liter might indicate Cushing's. This test requires a 48-hour hospital stay.
With the LDDST, a low dose of dexamethasone is taken, by mouth, every six hours for two days. Urine is collected once before the drug is taken and measured for cortisol. Urine is then collected several times on each day of the test for a comparison. Dexamethasone causes cortisol levels to drop, so if the levels fail to drop during the test, that may indicate Cushing's. The LDDST may not show cortisol changes in people with stress, depression, elevated estrogen levels or acute illness and may show a false-positive for Cushing's.
Treatment
If Cushing's syndrome is caused by a Pituitary tumor, doctors will often attempt to remove the tumor and treat the patient with cortisol-like drugs until their normal levels equalize. This surgery has an 80 percent cure rate. If surgery fails, or cannot be performed, then radiation therapy is another option. Radiation therapy usually lasts about six weeks with about a 40 to 50 percent success rate. Drug therapy is another option and there are several drugs that suppress cortisol production including mitotane, ketoconazole, metyrapone and aminoglutethimide. If the condition is caused by cancer, specialists remove the cancerous tissue and begin a course of chemotherapy.
Tags: Cushing syndrome, adrenal glands, Cortisol Test, Cushing disease, Cushing disease