Diagnosing Addison’s Disease

Dog Breeds

Because the symptoms of Addison’s disease, in which a dog’s adrenal glands produce insufficient hormones, are so similar to many other common ailments in dogs, it is a difficult problem to diagnose. A veterinarian often considers Addison’s as a possible factor only after eliminating other, more common canine problems.

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Introduction

Addison’s disease in dogs can be difficult to diagnose, because the symptoms of this disease are nonspecific and mimic those of many other, more common medical conditions, such as renal failure, liver disease and assorted gastrointestinal disorders. Veterinarians may only focus on Addison’s after eliminating other possible causes of a dog’s observable symptoms. If left untreated, this disease can progress to what is called an acute Addisonian crisis, which can rapidly become life-threatening. However, once Addison’s disease is properly diagnosed, it typically can be managed fairly well, and in most cases the symptoms can be controlled in short order.

Diagnosing Addison’s Disease in Dogs

Most veterinarians assessing a dog with a history of lethargy, weakness, abdominal pain, vomiting, diarrhea, inappetance and weight loss will recommend an initial database of blood work (a complete blood count and a serum biochemical profile) and a urinalysis. The results of these tests, together with the history and physical examination, may suggest a tentative diagnosis of Addison’s - particularly if they show low blood sodium levels (hyponatremia), low blood chloride levels (hypochloremia), high blood potassium levels (hyperkalemia) and high levels of blood urea nitrogen (BUN). However, these initial tests are not conclusive for the presence of Addison’s disease, and more advanced tests usually are required for a definitive diagnosis to be made.

The most definitive test for Addison’s is an ACTH stimulation test. ACTH is an abbreviation for adrenocorticotropic hormone, which is a hormone that in normal dogs stimulates the adrenal glands to produce other hormones that are called “corticosteroids,” or simply “steroids.” These adrenal hormones are extremely important to the regulation of a number of bodily functions, including metabolism and fluid management. The ACTH stimulation test involves administering ACTH to the patient and then reassessing its blood work to see whether its adrenal glands have responded appropriately by producing more steroid hormones. In a dog with functioning adrenal glands, the administration of ACTH will result in an increase in blood corticosteroid levels within a set period of time. In dogs with Addison’s disease, however, the ACTH injection will cause no or only minimal increase in the level of corticosteroids circulating in the blood, because the adrenal glands cannot react properly to the stimulus normally triggered by ACTH. This will confirm a diagnosis of Addison’s disease.

This may seem simple, but the clinical signs of Addison’s in dogs match the symptoms of so many other diseases that other diagnostic tests normally are done before an ACTH stimulation test to rule out those more common conditions. The results of these preliminary tests can point a veterinarian toward further testing for Addison’s if appropriate. For example, dehydration caused by vomiting and diarrhea - two common consequences of Adddison’s – typically leads to increased waste products in the dog’s circulation because the liquid component of blood is reduced. This shows up on blood test results as increased blood urea nitrogen (BUN). Elevated BUN may be caused by Addison’s, but it also may be caused by kidney disease. Because Addison’s can mimic kidney disease, dogs with elevated BUN levels often are given intravenous fluids in an attempt to correct their dehydration. If those dogs improve rapidly or dramatically, they may not have renal disease at all, because their kidneys are responding normally to increased fluid intake. In these cases, Addison’s will be increasingly suspected as the culprit.

It is this process of assessing the dog’s clinical signs, performing appropriate tests and eliminating disorders that are ruled-out by those tests that the veterinarian must go through to arrive at an accurate diagnosis. Only a veterinarian can definitively diagnose Addison’s disease. Although the diagnosis may take some time, it is possible for this disease to be diagnosed in time for effective treatment and management to begin. It is up to the dog’s owner to seek veterinary help as soon as possible symptoms of Addison’s are seen.

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Symptoms and Types