Causes

Too much of the hormone cortisol in your body causes Cushing syndrome. Cortisol, which is produced in the adrenal glands, plays a variety of roles in your body.

For example, cortisol helps regulate your blood pressure, reduces inflammation, and keeps your heart and blood vessels functioning normally. Cortisol helps your body respond to stress. It also regulates the way your body converts proteins, carbohydrates and fats in your diet into energy.

The role of corticosteroid medications (exogenous Cushing syndrome)

Cushing syndrome can develop from taking oral corticosteroid medications, such as prednisone, in high doses over time.

Oral corticosteroids may be necessary to treat inflammatory diseases, such as rheumatoid arthritis, lupus and asthma. They may also be used to prevent your body from rejecting a transplanted organ.

It's also possible to develop Cushing syndrome from injectable corticosteroids — for example, repeated injections for joint pain, bursitis and back pain. Inhaled steroid medicines for asthma and steroid skin creams used for skin disorders such as eczema are generally less likely to cause Cushing syndrome than are oral corticosteroids. But, in some individuals, these medications may cause Cushing syndrome, especially if taken in high doses.

Your body's own overproduction (endogenous Cushing syndrome)

The condition can be due to your body producing either too much cortisol or too much adrenocorticotropic hormone (ACTH), which 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, produces 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 ACTH-secreting tumor. Rarely, a tumor that develops in an organ that normally doesn't produce ACTH will begin to secrete this hormone in excess. 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. Disorders of the adrenal glands can cause them to produce too much cortisol. The most common is a noncancerous tumor of the adrenal cortex, called an adrenal adenoma, but only a small fraction of adenomas produce too much cortisol.

  Cancerous tumors of the adrenal cortex 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.