Addison’s Disease is uncommon in dogs and can be difficult to diagnose because it mimics many common medical conditions such as kidney failure, liver disease and gastrointestinal ailments. Veterinarians often focus on Addison’s only after eliminating other causes of the dog’s symptoms. Dogs with Addison’s usually present with a history of lethargy, weakness, abdominal pain, vomiting, diarrhea, poor appetite and weight loss. The veterinarian will perform a thorough physical examination, looking in the mouth, palpating the peripheral lymph nodes to see if they are enlarged, checking for obvious lumps and bumps, assessing the condition of the coat and skin, and listening to the heart and lungs. If Addison’s is the dog’s primary medical problem, its physical examination usually will be unremarkable.
Based on the dog’s symptoms and the results of the initial evaluation, most veterinarians will recommend routine blood work including complete blood count and serum biochemical profile, as well as a urinalysis. The results may suggest a tentative diagnosis of Addison’s – especially if they reveal low blood sodium levels (hyponatremia), low blood chloride levels (hypochloremia), high blood potassium levels (hyperkalemia) and high levels of circulating blood urea nitrogen (BUN). However, more advanced tests are required for Addison’s to be diagnosed definitively.
The most conclusive test for Addison’s is an adrenocorticotropic hormone (ACTH) stimulation test. In normal dogs, ACTH is produced by the pituitary gland and stimulates the adrenal glands to produce corticosteroids when the body needs them. The ACTH stimulation test involves measuring a dog’s blood steroid levels, and then administering ACTH. After a prescribed period of time, the levels of circulating corticosteroids will be reassessed. Dogs with Addison’s will have a barely detectable increase in blood steroid levels – or none at all, because their damaged adrenal glands can’t respond to the ATCH stimulus.
This sounds simple, however; because the signs of Addison’s Disease are so non-specific, the ACTH stimulation test usually is used only after other tests rule out more likely causes of the dog’s condition. For example, vomiting and diarrhea - two consequences of Addison’s – cause dehydration. Dehydrated dogs have a low blood volume with abnormally high levels of circulating solids. Basically, dehydration means that the fluid part of blood is too low, which makes the other components of blood too concentrated. These abnormalities can be detected on routine blood work. One of the easiest to identify is an increase in circulating blood urea nitrogen (BUN). Elevated BUN can be caused by Addison’s, because many Addisonian dogs are dehydrated. However, high BUN is much more commonly caused by kidney disease. Dogs with elevated BUN can be given intravenous fluids in an attempt to correct their dehydration and normalize their BUN levels. Dogs with kidney disease won’t improve dramatically after fluid therapy, because their kidneys can’t filter wastes from the blood regardless of their hydration level. However, BUN levels in dogs with Addison’s usually drop rapidly once they are rehydrated, because their kidneys respond normally to increased fluid levels. Most veterinarians diagnosing a dehydrated dog will therefore give them fluids before doing an ACTH stimulation test.
Although diagnosing Addison’s Disease can take some time, it usually is possible for veterinarians to diagnose it accurately in time for effective treatment to take place. By the time a dog is diagnosed, emergency medical treatment normally is necessary.