What causes Addison's disease?
The most common cause of Addison's disease is the destruction and/or shrinking (atrophy) of the adrenal cortex. In about 70% of all cases, this atrophy is believed to occur due to an autoimmune disorder. In an autoimmune disorder, the immune system of the body, responsible for identifying foreign invaders such as viruses or bacteria and killing them, accidentally begins to identify the cells of the adrenal cortex as foreign, and destroy them. In about 20% of all cases, destruction of the
adrenal cortex is caused by tuberculosis. The remaining cases of Addison's disease may be caused by fungal infections, such as histoplasmosis, coccidiomycosis, and cryptococcosis, which affect the adrenal gland by producing destructive, tumor-like masses called granulomas; a disease called amyloidosis, in which a starchy substance called amyloid is deposited in abnormal places throughout the body, interfering with the function of whatever structure it is present within; or invasion of the adrenal glands by cancer.
In about 75% of all patients, Addison's disease tends to be a very gradual, slowly developing disease. Significant symptoms are not noted until about 90% of the adrenal cortex has been destroyed. The most common symptoms include fatigue and loss of energy, decreased appetite, nausea, vomiting, diarrhea, abdominal pain, weight loss, muscle weakness, dizziness when standing, dehydration, unusual areas of darkened (pigmented) skin, and dark freckling. As the disease progresses, the patient may appear to have very tanned, or bronzed skin, with darkening of the lining of the mouth, vagina, and rectum, and dark pigmentation of the area around the nipples (aereola). As dehydration becomes more severe, the blood pressure will continue to drop and the patient will feel increasingly weak and light-headed. Some patients have psychiatric symptoms, including depression and irritability. Women lose pubic and underarm hair, and stop having normal menstrual periods.
When Dr. Thomas Addison's' first described this disease in London in 1855, the most common cause was tuberculosis. This remained the leading cause until the middle of the twentieth century when antibiotics progressively reduced TB's incidence. Since then, the major cause of Addison's disease results from an auto-immune reaction in which the body's immune system erroneously makes antibodies against the cells of the adrenal cortex and slowly destroys them. That process takes months to years. There are also several less common causes of Addison's disease: other chronic infections besides tuberculosis, especially certain fungal infections, invasion of the adrenal by cancer cells that have spread from another part of the body, especially the breast; CMV virus in association with AIDS; rarely, hemorrhage into the adrenals during shock; and the surgical removal of both adrenals.