What is Cushing's syndrome?

There are important substances in your body called glucocorticoids, which are steroid hormones produced in your adrenal glands. Glucocorticoids—particularly one called cortisol—help with many bodily processes, such as metabolism and your ability to fight infection. However, if something causes glucocorticoid levels to be too high for too long, many health problems may develop. Collectively, these health problems are referred to as Cushing’s syndrome.^1-3

Good to know:
Cushing’s syndrome is named for renowned neurosurgeon Harvey Cushing, who identified and described this condition in 1932.³

The causes of Cushing’s syndrome

As you just read, glucocorticoids are steroid hormones produced in your body. Glucocorticoids (both natural and
man-made) are also used in medicines for conditions such as allergies, respiratory problems, and skin problems.⁴

Cushing’s syndrome can develop when glucocorticoid levels in the body increase too much for too long due to either¹:

How much your body is making
Something is causing the adrenal gland(s) to overproduce cortisol. Doctors call this an “endogenous” (inside the body) cause.⁵

How much you’re taking
Certain medicine(s) may be continually adding too much glucocorticoid to the body. Doctors call this an “exogenous” (outside the body) cause.¹

In the majority of cases, Cushing’s syndrome develops when a person has been regularly taking more glucocorticoid-containing medicine than his or her body can handle (an exogenous cause).^1,5 But in the other cases, Cushing’s syndrome is usually due to a tumor (an endogenous cause). A tumor is when abnormal cells build up and form a lump.^1,5

Statistics on endogenous Cushing’s syndrome

According to statistics, Cushing’s syndrome due to an endogenous cause is uncommon.¹ Estimates vary, but up to 13 people per million have endogenous Cushing’s syndrome, and it occurs more often in women than men.^1,3 Experts believe, however, that the number of people with endogenous Cushing’s syndrome may be higher than indicated by statistics.¹

In more than 2 out of 3 people with endogenous Cushing’s syndrome, the cause is a tumor in the pituitary gland. Fortunately, this type of tumor is typically benign. A benign pituitary tumor is called an adenoma. Unlike a cancerous (malignant) tumor, a benign tumor stays in its original location and will not spread.^1,3,6

When a pituitary tumor is the source of the problem, the condition is referred to as Cushing’s disease.¹

Possible causes of Cushing's Syndrome

More about pituitary tumors and Cushing’s disease

Adrenocorticotropic hormone, or ACTH, is a hormone produced in your pituitary gland. ACTH travels to your adrenal glands and tells them to produce cortisol (see diagram below).⁴

Diagram of how Cushing’s Syndrome affects the body

If a person has an ACTH-producing pituitary tumor, it means that a cluster of abnormal cells has built up in the pituitary gland. These abnormal cells produce ACTH, just as normal pituitary gland cells do—only far too much.⁷

The excess ACTH travels to adrenal glands. The adrenal glands are then bombarded with signals to make more and more cortisol. As a result, the adrenal glands continuously produce too much cortisol.²

Extrapituitary tumors and Cushing’s syndrome

About 10% of Cushing’s syndrome cases are caused by excess ACTH produced by a tumor that is not in the pituitary gland. This is called ectopic ACTH production. The majority of these tumors are bronchial, thymic or pancreatic carcinoids, islet cell pancreatic tumors, medullary thyroid cancer, and pheochromocytomas.¹

Adrenal tumors and Cushing’s syndrome

Cushing’s syndrome can also be caused by a benign or malignant tumor in the adrenal gland producing too much cortisol. Adrenal tumors are responsible for Cushing’s syndrome in fewer than 1 in 5 cases. In rare cases, other growths in the adrenal gland will cause Cushing’s syndrome.^5,8

Next, read about signs and symptoms of Cushing’s syndrome.

References: 1. Newell-Price J, Bertagna X, Grossman AB, Nieman LK. Cushing’s syndrome. Lancet. 2006;367:1605-1617. 2. Nieman LK, Ilias I. Evaluation and treatment of Cushing’s syndrome. Am J Med. 2005;118:1340-1346. 3. Lin DD, Loughlin KR. Diagnosis and management of surgical adrenal diseases.
J Urol. 2005;66:476-483. 4. Dorland’s Online Dictionary Web site. Available at: http://www.dorlands.com. Accessed October 2, 2009. 5. Arnaldi G, Angeli A, Atkinson AB, et al. Diagnosis and complications of Cushing’s syndrome: a consensus statement. J Clin Endocrinol Metab. 2003;88:5593-5602.
6. Pathophysiology of disease: disorders of the hypothalamus & pituitary gland. Access Medicine Web site. http://www.accessmedicine.com/content.aspx?aID=2090603 Accessed July 30, 2009. 7. Else T,
Hammer GD, Lingappa VR. Disorders of the hypothalamus & pituitary gland. Available at: http://www.accessmedicine.com.ezp-prod1.hul.harvard.edu/content.aspx?aID=2090603. Accessed July 14, 2009. 8. Biller BMK, Grossman AB, Stewart PM, et al. Treatment of adrenocorticotropin-dependent Cushing’s syndrome: a consensus statement. J Clin Endocrinol Metab. 2008;93:2454-2462.