What causes Addison’s disease?
Addison’s disease may be caused by a disorder of the adrenal glands (primary adrenal insufficiency). The disease may also be caused if the pituitary gland stops producing enough adrenal stimulating hormone (secondary adrenal insufficiency). In most cases, primary adrenal insufficiency occurs as a result of the body’s own immune system slowly destroying the outer layer of the adrenal glands. This form of Addison’s is what is known as an autoimmune disease and accounts for about 80% of cases. In developed countries, tuberculosis (TB) accounts for about 20% of cases of primary adrenal insufficiency when the adrenal glands are destroyed by the infection.

When Dr. Thomas Addison first identified the disease in 1849, TB was the most common cause of the disease. Other less common causes of primary adrenal insufficiency are chronic infections, cancer cells that spread to the adrenal glands from other parts of the body, and surgical removal of the adrenal glands. Secondary adrenal insufficiency is caused by a reduction in the amount of adrenal stimulating hormone (ACTH) produced by the pituitary gland. In most cases, secondary adrenal insufficiency is caused by a pituitary tumor. It may also occur when high doses of steroids are used for long periods to treat other diseases such as asthma, causing temporary or permanent loss of adrenal function.

What tests confirm a diagnosis of Addison’s disease?
An ACTH stimulation test is used to diagnose Addison’s disease. For this test, levels of cortisol in the blood and/or urine are measured before and after an intravenous injection (into a vein) of a synthetic form of adrenal stimulating hormone. Cortisol levels are measured 30–60 minutes after the injection. Levels should rise during this time but, if there is adrenal insufficiency, there may be little or no rise in cortisol levels. If the results of this test are abnormal, a longer test will be carried out. Your doctor will explain these tests to you. Another test that may be used is an insulin-induced hypoglycemia test. For this test, blood glucose and cortisol levels are measured, and an injection of a fast-acting insulin is then administered. The levels are measured again at 30, 45, and 90 minutes following the injection. The normal response is for blood glucose levels to fall and cortisol levels to rise. Secondary adrenal insufficiency may be caused by a pituitary problem so a CT scan of the pituitary gland may be ordered.