Addison's disease is a rare endocrine or hormonal disorder that occurs when the adrenal glands do not produce enough of the hormone cortisol and in some cases, the hormone aldosterone. The progressive loss of adrenal hormones usually produces a chronic, steadily worsening fatigue, loss of appetite and weight loss, muscle weakness, low blood pressure, nausea and vomiting, and sometimes darkening of the skin in both exposed and non-exposed parts of the body.
Classical Addison's disease results from a loss of both cortisol and aldosterone secretion due to the near total or total destruction of both adrenal glands. This condition is also called primary adrenal insufficiency. If ACTH is deficient, there will not be enough cortisol produced, although aldosterone may remain adequate. This is secondary adrenal insufficiency, which is distinctly different, but similar to Addison's disease, since both include a loss of cortisol secretion.
The slowly progressive chronic symptoms are usually missed or ignored until a sudden event like a flu virus, an accident, or the need for surgery suddenly precipitates a dramatic change for the worse because of the deficient response from the adrenals to one of these stresses. This is referred to as an Addisonian crisis and is a medical emergency.
Cortisol is normally produced by the adrenal glands, located just above the kidneys. It belongs to a class of hormones called glucocorticoids, which affect almost every organ and tissue in the body. Cortisol has possibly hundreds of effects in the body. Its most important job is to help the body respond to stress. Among its other vital tasks, cortisol: helps maintain blood pressure and cardiovascular function; helps slow the immune system's inflammatory response; helps balance the effects of insulin in breaking down sugar for energy; and helps regulate the metabolism of proteins, carbohydrates, and fats.
Because cortisol is so vital to health, the amount of cortisol produced by the adrenals is precisely balanced. Like many other hormones, cortisol is regulated by the brain's hypothalamus and the pituitary gland, a bean-sized organ at the base of the brain. First, the hypothalamus sends "releasing hormones" to the pituitary gland. The pituitary responds by secreting other hormones that regulate growth, thyroid and adrenal function, and sex hormones such as oestrogen and testosterone. One of the pituitary's main functions is to secrete ACTH (adrenocorticotropin), a hormone that stimulates the adrenal glands. When the adrenals receive the pituitary's signal in the form of ACTH, they respond by producing cortisol. Completing the cycle, cortisol then signals the pituitary to lower secretion of ACTH. Aldosterone belongs to a class of hormones called mineralocorticoids, also produced by the adrenal glands. It helps maintain blood pressure and water and salt balance in the body by helping the kidney retain sodium and excrete potassium. When aldosterone production falls too low, the kidneys are not able to regulate salt and water balance, causing blood volume and blood pressure to drop.
Addison's disease affects about 1 in 100,000 people. It occurs in all age groups and afflicts men and women equally. A study in London showed thirty-nine cases per million population as of 1960. Twelve were due to tuberculosis. In the non-tuberculosis group, women were three times more likely to have Addison's disease. Extrapolation of these figures to the U.S. would give about 8,800 cases, but this is probably an underestimation.