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Causes
By Mayo Clinic staff
Your endocrine system consists of glands that produce hormones, which 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's syndrome.
The role of corticosteroids
Cushing's syndrome can develop from a cause that originates outside of your body (exogenous Cushing's syndrome). Taking corticosteroid medications in high doses over an extended period of time may result in Cushing's syndrome. These medications, such as prednisone, dexamethasone (Decadron) and methylprednisolone (Medrol), 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's 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 (for skin disorders such as eczema) are in the same general category of drugs, they're generally not implicated in Cushing's syndrome unless taken in very high doses.
Your body's own overproduction
The condition may also be due to your body's own overproduction of cortisol (endogenous Cushing's 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's syndrome may be related to:
- A pituitary gland tumor. 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's disease. It occurs much more often in women and is the most common form of endogenous Cushing's 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's syndrome. These tumors, which can be noncancerous (benign) or cancerous (malignant), are usually found in the lung, pancreas, thyroid or thymus gland.
- A primary adrenal gland disease. In some people, the cause of Cushing's 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 are rare, but they can cause Cushing's syndrome as well. Occasionally, benign, nodular enlargement of both adrenal glands can result in Cushing's syndrome.
