Cushing’s syndrome (CS) is caused by over-production of a type of hormone called glucocorticoids. The most important one is called cortisol. These hormones are made by the adrenal cortex. Glucocorticoids regulate how the body handles protein and glucose. They affect immunology and the inflammatory response. They influence blood pressure and the bodies’ response to stress.
Secretion of these hormones are stimulated by a hormone from the brain called adrenocotical tropic hormone (ACTH). Measurement of this hormone helps us determine the cause of excess cortisol secretion. CS can develop in several ways and is a complicated subject. For our discussion, we will only consider CS that occurs due to excess cortisol production from a tumor of the adrenal gland. This accounts for about 20% of all cases of CS.
Patients with CS suffer from obesity, especially in the central body and face. The arms and legs are relatively thin. Fat deposits may develop on the upper back, adjacent the neck (buffalo hump). High blood pressure occurs in most patients. Muscle weakness and muscle wasting is common. The skin becomes thin and easily damaged. Red and blue stretch marks may appear on the abdomen.
The diagnosis of CS is made when the patient has these clinical features and excess glucocorticoid secretion is proven. Most commonly this is done by measuring the amount of cortisol in the urine over a 24 hour period. Care is taken to ensure that the patient is not taking medications that could elevate cortisol levels falsely. Secretion of these hormones can vary widely and are influenced by many things. Misleading results are not uncommon and other confirmatory tests may be required. These are best done under the supervision of an experienced endocrinologist.
Once the diagnosis of CS has been made the cause (source) of the excess cortisol secretion must be determined. The is done by measuring the amount of ACTH in the blood. If ACTH is elevated then a cause outside the adrenal gland is likely (most commonly a tumor of the gland in the brain that makes ACTH, this is known as Cushing’s disease). If the amount of ACTH in the blood is low them the source of excess cortisol secretion is likely from the adrenal gland. A dexamethasone suppression test may be performed to clarify whether or not CS is do to over-production of ACTH. If the excess cortisol is not due to over production of ACTH then an adrenal source is very likely. About 2/3’s of these cases will be due to benign tumors. About 1/3 of cases will be due to adrenalcortical cancer. Rarely, diffuse over-growth of the cortex of both adrenal glands may be the problem (hyperplasia).
After the diagnosis is made and the source confirmed to the adrenal gland, we perform imaging studies such as a CT scan or MRI. This usually reveals the tumor in one of the adrenal glands and an operative approach can be organized. Our recommended approach is a laparoscopic adrenalectomy. Pre-op and post-op issues are considered on another page. As mentioned above, a malignant tumor may be the cause of CS. Large tumors (> 6 cm) or tumors with evidence of local invasion or metastasis on CT scan are worrisome findings. Measurement of a hormone precursor (DHEA) is frequently elevated when the tumor is malignant. Malignant tumors may be best treated with traditional adrenalectomy.