Initial Evaluation

Addison’s Disease can be difficult to diagnose because it is relatively uncommon in dogs, and also because its symptoms mimic those of many more common medical conditions, such as kidney failure, liver disease and gastrointestinal disorders. Veterinarians usually focus on Addison’s only after they eliminate other possible causes of the dog’s symptoms. When assessing a dog with a history of lethargy, weakness, abdominal pain, vomiting, diarrhea, poor appetite and weight loss, the attending veterinarian will first perform a thorough physical examination. This includes looking in the mouth, palpating (feeling) the peripheral lymph nodes to see if they are enlarged, checking all over the body for lumps and bumps, assessing the condition of the coat and skin, and auscultating (listening to) the heart and lungs through a stethoscope. If Addison’s is the dog’s only medical problem, its physical examination results usually will be unremarkable.

Diagnostic Procedures

Based on the dog’s symptoms and the results of the initial examination, most veterinarians will recommend conducting some basic blood work (a complete blood count and a serum biochemical profile) and a urinalysis. These routine tests, which involve collecting and evaluating blood and urine samples, are simple and relatively inexpensive. The results, together with the history and physical examination, 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), which is a waste product of metabolism. However, more advanced tests are required for Addison’s to be definitively diagnosed.

The most conclusive test for Addison’s Disease is an “ACTH stimulation test.” “ACTH” is an abbreviation for “adrenocorticotropic hormone,” a substance that is produced by the pituitary gland and, in normal dogs, stimulates the adrenal glands to produce other hormones, called “corticosteroids” or simply “steroids.” Adrenal hormones are extremely important to the regulation of a number of bodily functions, including metabolism and fluid management. Dogs with Addison’s have abnormally low levels of circulating adrenal steroids, which is why the disease medically is called “hypoadrenocorticism.” The ACTH stimulation test involves administering ACTH, waiting a prescribed period of time and then reevaluating the dog’s blood to see whether its adrenal glands have responded appropriately by producing more corticosteroids. In dogs with Addison’s Disease, the ACTH injection will cause no or only a barely detectable increase in circulating steroids, because the adrenal glands are damaged and cannot respond normally to the ATCH stimulus.

This may seem simple. However, because the signs of Addison’s Disease match those of so many more common disorders, ACTH stimulation tests usually are conducted only after other tests have ruled out more likely causes of the dog’s condition. For example, vomiting and diarrhea - two common consequences of Adddison’s – cause dehydration. Dehydrated dogs have abnormally low levels of circulating fluids, including blood, and abnormally high levels of circulating solids, including toxic waste products. These abnormalities can be detected on routine blood work. One of the easiest to identify is an increase in circulating blood urea nitrogen. Elevated BUN can be caused by Addison’s. However, more often it is caused by kidney disease. Dogs with elevated BUN often are given intravenous fluids in an attempt to correct their dehydration and normalize circulating BUN levels. Dogs with kidney disease won’t improve dramatically, because their kidneys are unable to filter out wastes regardless of their hydration level. On the other hand, BUN levels in dogs with Addison’s Disease usually drop rapidly once hydration has been reestablished, since their kidneys are fine and can respond normally to increased fluid levels.

Attending veterinarians must systematically go through this process of assessing a dog’s history, symptoms and physical state, performing appropriate tests and ruling-out the more common causes of its condition, in order to reach the right diagnosis. Although this can take some time, it usually is possible for Addison’s to be diagnosed in time for effective treatment to take place.

Special Notes

If undiagnosed and untreated, Addison’s can progress to what is called an “acute Addisonian crisis,” which may rapidly become life-threatening.