This has been the most commonly asked question we've gotten since announcing his diagnosis to family and friends. I've been likening it to diabetes, to give them the scope of what this means for him and for us. It requires daily medication. It requires a lifestyle change. It requires regular blood draws to determine how the medication is working. Etc.
But, a more technical explanation, for the curious, would be this (as taken from the PWDCA and AddisonDogs websites):
Addison's disease is caused when the adrenal glands deteriorate. These small hormone producing glands are located above each kidney and are important for controlling the metabolism of sugar and maintaining the salt and water balances in the body.
The adrenal gland is made up of two layers, the cortex and the medulla. The outer area, or cortex, secretes corticosteroid hormones such as cortisol and aldosterone. The medulla, part of the sympathetic nervous system, secretes epinephrine (adrenaline), which is generally not affected by Addison’s.
There are three forms of Addison’s disease: primary, secondary and atypical. Primary and atypical Addison’s are usually the result of immune mediated damage to the glands. Secondary hypoadrenocorticism is from failure of the pituitary to stimulate the adrenals with adrenocorticotropic hormone (ACTH).
As the adrenal glands cease to produce vital hormones, physical and behavioral symptoms develop, sometimes in an inconsistent manner, so an owner might observe one or any combination of signs: depression, lethargy or weakness, vomiting, diarrhea, weight loss, and/or a lack of interest in food. These symptoms may come and go over months, making diagnosis difficult.
Addison's Disease is often called the Great Pretender because it presents symptoms of dozens of other diseases. Many veterinarians spend time testing for kidney disease, Lyme, cancer, blockages in the digestive tract, upset stomach, etc. etc. About 30% of dogs are only diagnosed when they're in a full-fledged crisis. Most dogs aren't diagnosed until they're incredibly ill. The average age of the dog at diagnosis is between 4-7 years of age (Lucky was 1 week shy of his 3rd birthday).
Some breeds of dogs seem to be more predisposed to developing Addison's: Leonbergers, Standard Poodles, Nova Scotia Duck Tolling Retrievers, Airedales, Bearded Collies, German Shepherd Dog, German Shorthair Pointer, Great Dane, Labrador Retriever, St. Bernard, English Springer Spaniel, West Highland White Terrier, Wheaten Terrier, and Portuguese Water Dog.
This is by no means an exhaustive list. And Addison's Disease can develop in any breed or mix. If your dog exhibits any of the symptoms on the list above, consider Addison's as a possible, perhaps even probable, culprit.
The good news is that, while not curable, Addison's is 100% treatable. With proper medication, Addison Dogs live happy, full, long lives.