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Causes

By Mayo Clinic staff

Cushing syndrome results from excess levels of the hormone cortisol in your body. Your endocrine system consists of glands that produce hormones that regulate processes throughout your body. These glands include the adrenal glands, pituitary gland, thyroid gland, parathyroid glands, pancreas, ovaries (in females) and testicles (in men).

Your adrenal glands produce a number of hormones, including cortisol. Cortisol plays a variety of roles in your body. For example, cortisol helps regulate your blood pressure and keeps your cardiovascular system functioning normally. It also helps your body respond to stress and regulates the way you convert (metabolize) proteins, carbohydrates and fats in your diet into usable energy. However, when the level of cortisol is too high in your body, you may develop Cushing syndrome.

The role of corticosteroids
Cushing syndrome can develop from a cause that originates outside of your body (exogenous Cushing syndrome). Taking corticosteroid medications in high doses over an extended period of time may result in Cushing syndrome. These medications, such as prednisone, have the same effects as does the cortisol produced by your body.

Your doctor may prescribe corticosteroids to treat inflammatory diseases, such as rheumatoid arthritis, lupus and asthma, or to prevent your body from rejecting a transplanted organ.  Because the doses required to treat these conditions are often higher than the amount of cortisol your body normally needs each day, the effects of excess cortisol can occur.

People can also develop Cushing syndrome from injectable corticosteroids — for example, repeated injections for joint pain, bursitis and back pain. While certain inhaled steroid medicines (taken for asthma) and steroid skin creams (used for skin disorders such as eczema) are in the same general category of drugs, they're less likely to cause Cushing syndrome, but may in some individuals especially if taken in high doses.

Your body's own overproduction
The condition may also be due to your body's own overproduction of cortisol (endogenous Cushing syndrome). This may occur from excess production by one or both adrenal glands, or overproduction of the adrenocorticotropic hormone (ACTH), which normally regulates cortisol production. In these cases, Cushing syndrome may be related to:

• A pituitary gland tumor (pituitary adenoma). A noncancerous (benign) tumor of the pituitary gland, located at the base of the brain, secretes an excess amount of ACTH, which in turn stimulates the adrenal glands to make more cortisol. When this form of the syndrome develops, it's called Cushing disease. It occurs much more often in women and is the most common form of endogenous Cushing syndrome.
• An ectopic ACTH-secreting tumor. Rarely, when a tumor develops in an organ that normally does not produce ACTH, the tumor will begin to secrete this hormone in excess, resulting in Cushing syndrome. These tumors, which can be noncancerous (benign) or cancerous (malignant), are usually found in the lungs, pancreas, thyroid or thymus gland.
• A primary adrenal gland disease. In some people, the cause of Cushing syndrome is excess cortisol secretion that doesn't depend on stimulation from ACTH and is associated with disorders of the adrenal glands. The most common of these disorders is a noncancerous tumor of the adrenal cortex, called an adrenal adenoma. Cancerous tumors of the adrenal cortex (adrenocortical carcinomas) are rare, but they can cause Cushing syndrome as well. Occasionally, benign, nodular enlargement of both adrenal glands can result in Cushing syndrome.
• Familial Cushing syndrome. Rarely, people inherit a tendency to develop tumors on one or more of their endocrine glands, affecting cortisol levels and causing Cushing syndrome.

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