Cushing syndrome can be difficult to diagnose, particularly endogenous Cushing syndrome, because other conditions share the same signs and symptoms. Diagnosing Cushing syndrome can be a long and extensive process. You may not have any firm answers about your condition until you've had a series of medical appointments.
Your doctor will conduct a physical exam, looking for signs of Cushing syndrome. He or she may suspect Cushing syndrome if you have signs such as rounding of the face (moon face), a pad of fatty tissue between the shoulders and neck (buffalo hump), and thin skin with bruises and stretch marks.
If you've been taking a corticosteroid medication for a long time, your doctor may suspect that you've developed Cushing syndrome as a result of this medication. If you haven't been using a corticosteroid medication, these diagnostic tests may help pinpoint the cause:
Urine and blood tests. These tests measure hormone levels in your urine and blood and show whether your body is producing excessive cortisol. For the urine test, you may be asked to collect your urine over a 24-hour period. Both the urine and blood samples will be sent to a laboratory to be analyzed for cortisol levels.
Your doctor might also recommend other specialized tests that evaluate the blood and urine to help determine if Cushing syndrome is present and to help identify the underlying source of any excess production. These tests often involve measuring cortisol levels before and after stimulation or suppression with other hormone medications.
- Saliva test. Cortisol levels normally rise and fall throughout the day. In people without Cushing syndrome, levels of cortisol drop significantly in the evening. By analyzing cortisol levels from a small sample of saliva collected late at night, doctors can see if cortisol levels are too high, suggesting a diagnosis of Cushing syndrome.
- Imaging tests. Computerized tomography scans or magnetic resonance imaging scans can provide images of your pituitary and adrenal glands to detect abnormalities, such as tumors.
Petrosal sinus sampling. This test can help determine whether the cause of endogenous Cushing syndrome is rooted in the pituitary or somewhere else. For the test, blood samples are taken from the petrosal sinuses — veins that drain the pituitary glands.
A thin tube is inserted into your upper thigh or groin area while you're sedated, and threaded to the petrosal sinuses. Levels of ACTH are measured from the petrosal sinuses, and from a blood sample taken from the forearm.
If ACTH is higher in the sinus sample, the problem stems from the pituitary. If the ACTH levels are similar between the sinus and forearm, the root of the problem lies outside of the pituitary gland.
These tests don't only help your doctor diagnose Cushing syndrome, they may also help rule out other medical conditions with similar signs and symptoms. For example, polycystic ovary syndrome — a hormone disorder in women with enlarged ovaries — shares some of the same signs and symptoms as Cushing has, such as excessive hair growth and irregular menstrual periods. Depression, eating disorders and alcoholism also can partially mimic Cushing syndrome.