Addison's disease, also known by its medical term hypoadrenocorticism, is an adrenal gland disorder that causes hormonal imbalances in the body. The condition is named after Thomas Addison, a British scientist credited for being the first person to demonstrate adrenal glands are necessary for life.
The adrenal glands are small hormone-producing glands located in the abdomen next to each kidney in dogs, cats, people, and other species. To understand how Addison’s disease affects your pet, it is first important to understand the importance of the adrenal glands and the hormones they produce.
The adrenal glands produce two classes of hormones – glucocorticoids and mineralocorticoids – that are critical for life. After theses hormones have been synthesized by the adrenal glands, they are secreted into the bloodstream and circulate throughout the body. Both of these hormones have an effect on the function of cells everywhere in the body.
Glucocorticoids are natural cortisone, which is necessary for life. Glucocorticoids have many functions, including affecting appetite and supporting immune system function. Cortisone can be beneficial as a medical treatment for relatively minor problems (e.g., poison oak) and for serious life-threatening medical disorders (e.g., immune hemolytic anemia), as it minimizes the body’s immune response. If an individual has too much or too little cortisone in their system, and suffers from this problem chronically, serious medical problems can result.
Mineralocorticoids control the levels of sodium and potassium (two of the body's critical salt concentrations) in the bloodstream. As with glucocorticoids, too much mineralocorticoid in the system usually results in serious medical problems. Too little mineralocorticoid is a life-threatening condition.
Addison's disease occurs when there is a loss of these hormones in the in the body. There could be a shortage of either glucocorticoids or mineralocorticoids; there also could be a shortage of both hormones simultaneously.
The imbalance of glucocorticoids and mineralocorticoids in the bloodstream is most often caused by damage to the adrenal glands, specifically their hormone-producing cells. This damage prevents the adrenal glands from being able to produce the essential hormones. The most common cause of Addison's disease is the destruction of both adrenal glands by their own immune system. Other, but less common, causes of Addison's disease include cancers and infections that can invade and destroy the adrenal glands.
The immune system normally functions by constantly being on the lookout for foreign objects and, once they are identified, tagging those foreign substances for destruction. This is how the immune system protects the body from viruses and bacteria. With Addison’s disease, however, your pet’s immune system mistakenly tags its own adrenal glands as invaders and sets out to eliminate them. It is not well understood why the immune system would attack the body in addition to protecting it.