Causes of Addison’s Disease
Veterinarians are not always able to determine why their patients develop Addison’s Disease. In the most general sense, Addison’s is caused by some severe insult to the outer layer (cortex) of one or both of the adrenal glands, which causes all or part of the cortex to waste away. This, in turn, reduces or eliminates production and secretion of the corticosteroid hormones that are critical to normal body function. One of the most recognized causes of Addison’s Disease in dogs is autoimmune-mediated destruction of the adrenal cortices. Autoimmune disorders occur when a dog’s complex, finely-tuned immune system malfunctions and starts to attack the dog’s own tissues – in this case, the adrenal glands. Immune-mediated Addison’s in dogs usually happens for no known reason; this is called “idiopathic” Addison’s.
Other things that can damage the adrenal cortex include:
- Ingestions of toxic drugs or chemicals
- Physical trauma
- Adrenal tumors/cancer
- Genetic predisposition
- Granulomatous disease (histoplasmosis, tuberculosis and blastomycosis can lead to formulation of tumor-like masses of granulation tissue in the adrenal glands)
- Administration of the drug mitotane to treat Cushing’s Disease
- Adrenocortical amyloidosis
- Long-term administration of steroid hormones. Over time, steroid therapy suppresses the body’s normal production of corticosteroids, because they are coming in sufficient amounts from the outside. This can cause the adrenal glands to atrophy from disuse and become non-functional.
When there are not enough corticosteroid hormones circulating through a dog’s bloodstream, the levels of glucose, potassium, sodium and chloride can quickly become imbalanced. This, in turn, can cause severe dehydration, depletion of the normal volume of circulating blood and significant problems with the animal’s heart and other vital organs. This is what is known as an “Addisonian crisis.” A dog in an Addisonian crisis must be hospitalized immediately and treated aggressively to have a realistic chance of pulling through.
An acute Addisonian crisis can happen when corticosteroid drugs that have been administered to a dog for a long time are abruptly withdrawn. While the dog is receiving the steroids, its adrenal glands go into a sort of resting state. When the external steroids are stopped, the dog can develop an extremely serious shortage of circulating adrenal hormones, which can cause shock and cardiovascular collapse. If the adrenal glands have atrophied or been “resting” for too long, the dog may not recover.
Ultimately, anything that damages the adrenal glands’ ability to produce a normal amount of corticosteroids can contribute to Addison’s Disease in dogs.
Prevention of Addison’s Disease
There is no fool-proof way to prevent canine Addison’s Disease, since the exact causes of this ailment are unclear. Avoiding abdominal trauma and weaning dogs off long-term steroid therapy can prevent some types of hypoadrenocorticism.
If diagnosis and treatment are delayed for too long, Addison’s Disease can be fatal.