Cushing’s syndrome is a disease in which the body makes too much cortisol. Cortisol is a steroid that is made by the adrenal glands. Cortisol is necessary for daily life and helps the body respond to stressful events, regulates the sleep-wake cycles, and helps regulate the body’s response to inflammation. A special part of the brain called the pituitary makes a hormone called adrenocorticotrophic hormone (ACTH) that controls the release of cortisol from the adrenal glands. Although cortisol is essential to life, constantly high levels of cortisol can damage the entire body.
The main causes of Cushing’s syndrome are ACTH-dependent disease (when the body makes too much ACTH which in turn increases the cortisol production), ACTH-independent disease (when the adrenal is making too much cortisol and the ACTH is therefore low), and iatrogenic disease (when the patient is taking prescription steroids). Prescription steroids called glucocorticoids, like prednisone, are used to treat patients who had a transplant or who have diseases such as rheumatoid arthritis, asthma, or inflammatory bowel disease. Even if the patient is taking the right dose of steroid for their condition, they may develop Cushing’s syndrome. ACTH-dependent and -independent disease can be caused by the following sources:
- ACTH-dependent disease:
- Pituitary Adenoma (also known as Cushing’s Disease)
In this condition, a small tumor causes increased ACTH production. Pituitary adenomas are the most common cause of Cushing’s syndrome and makes up about 70% of cases.
- Ectopic ACTH-producing Tumor
In this rare condition, a tumor outside of the pituitary is making too much ACTH. These tumors are most commonly found in the lung and thymus gland, but have also been found in the thyroid, ovary, adrenal gland, and liver.
- ACTH-independent Disease
- In this condition, either both adrenal glands are hyperactive or there is an adrenal tumor that is making too much cortisol. Adrenal tumors cause about 30% of cases of Cushing’s Syndrome. Although most of these tumors are benign, they can rarely be adrenal cancers