Addison's Disease in Dogs

Addison's disease in dogs is the result of low hormone output from the adrenal glands and is a condition that can make a dog become very ill. When the adrenal glands are not functioning it causes a cascade of problems, including imbalanced electrolytes including elevated levels of potassium in the blood that can lead to heart problems. Understanding the symptoms, most of which are non-specific, can alert you to get your dog the treatment that it needs.

What Is Addison's Disease?

The scientific term for Addison's disease is hypoadrenocorticism, which generally means "low adrenal hormones." Addison's disease occurs when the adrenal glands do not produce an adequate amount of the hormones necessary to keep the body's electrolytes in balance.

The adrenals are tiny glands located near the kidneys. When a dog experiences stress, normal adrenal glands will produce extra cortisol to help the body adjust to the physiological effects of stress. However, the body cannot continue to function normally if it cannot produce enough cortisol. The water and electrolytes in the body become out of balance, leading to serious illness.

Addison’s disease is most common in young to middle-aged dogs. It is much less common than the opposite condition in dogs, Cushing’s disease, which causes an overproduction of cortisol.

Symptoms of Addison's Disease in Dogs

Dogs with Addison's disease may not exhibit any symptoms at first. When signs do appear, they can vary from mild to severe. Be aware that the signs of Addison's disease may be vague and are similar to the signs of other illnesses. If you notice these or any other signs of illness that last more than a day or two, you should see your veterinarian.

Vomiting and Diarrhea

If your pet has Addison's disease, the condition will affect its gastrointestinal system and cause vomiting and diarrhea. Sometimes these two symptoms happen to a dog rapidly, causing it to become severely dehydrated.

Lethargy and Weakness

A dog with an electrolyte imbalance will not function well. That's because the imbalance forces fluids to move out of your pet's cells, leaving the body tired, listless, and weak.

Shaking

Infrequently, a dog might have intermittent shaking episodes if it has Addison's disease. You may only notice slight trembling.

Slow Heart Rate

Because Addison's causes potassium to build up in your dog's blood, it can affect the heart, causing it to dangerously slow down or beat irregularly. If a dog's heartbeat is extremely low, it can become extremely weak and possibly go into shock.

Unexplained Weight Loss

Increasing episodes of vomiting, diarrhea, a loss of appetite, and subsequent dehydration will cause a dog with the condition to lose a lot of weight rapidly.

Causes of Addison's Disease

There are two types of Addison's disease—primary and secondary. Primary Addison's occurs spontaneously and without seeming cause while secondary Addison's happens with cause. The exact cause of primary Addison's disease is not known. It is believed to occur due to immune-mediated destruction of the adrenal tissue. Secondary Addison's occurs after some kind of damage has been done to the adrenal glands due to an outside factor. Such factors can include trauma, a tumor in the pituitary gland that controls hormones, an infection, or even medications used to treat other diseases.

Certain dog breeds may be predisposed to Addison's disease, including, but not limited, to the following:

• Bearded collies
• Great Danes
• Labrador retrievers
• Leonbergers
• Nova Scotia duck tolling retrievers
• Portuguese water dogs
• Standard poodles
• West Highland white terriers

Diagnosing Addison's Disease in Dogs

Your veterinarian will begin by discussing your pet's medical history and current signs. Next, a physical examination will be performed. Dogs with Addison's may have dehydration, weak pulses, and/or a slow, irregular heart rate. However, lab tests will be necessary to determine the true cause of your dog's symptoms. Your vet will likely start with routine lab tests, like blood chemistry with electrolytes and a complete blood count. A urinalysis may also be necessary.

In dogs with Addison's disease, it is common for blood work to show some or all of the following issues:

• A high potassium level indicates a sign of an electrolyte imbalance.
• A low sodium level also signals an electrolyte imbalance.
• Kidney values may be affected.
• A CBC (complete blood count) may be abnormal.
• A urinalysis may be abnormal.

A presumptive diagnosis of Addison's disease may be made based on the initial test results, but additional testing is necessary to confirm the diagnosis. In most cases, the next step is an ACTH stimulation test to check the adrenal's response to the adrenocorticotropic hormone. These results will confirm if Addison's disease is present. An ACTH stimulation test is performed over a few hours in your vet's office and involves the following:

• A preliminary blood sample is drawn to establish a baseline cortisol level.
• Next, an injection of ACTH is given to stimulate the adrenal glands to produce cortisol.
• Then a post-injection blood sample is drawn one to two hours later to measure the cortisol levels again. If the cortisol level in the blood did not rise as expected, a diagnosis of Addison's may be made.

Because other factors may affect your dog's cortisol levels, a non-definitive test result may warrant further diagnostic testing. Your vet will interpret all results and discuss the next steps for your dog.

Treatment

If a dog with Addison's disease becomes even slightly sick, it is essential to have it seen by a vet as soon as possible. An Addisonian crisis can occur at any time at which point your dog will be very weak and experience vomiting and/or diarrhea. The electrolyte imbalance requires careful correction with fluid therapy and medications in order to avoid further complications so the faster your dog can begin treatment, the less serious the crisis becomes. Expect the following if your dog is ill with Addison's:

• Hospitalization: A very sick dog with Addison's will typically need to be hospitalized until stabilized.
• Medication: Fortunately, most cases of Addison's disease can be managed with medication once the dog's electrolytes have been regulated.
• Replacement therapy: Ongoing maintenance of the Addison's dog typically involves the replacement of glucocorticoids (usually prednisone), and most patients require the replacement of mineralocorticoids with either desoxycorticosterone pivalate or fludrocortisone.
• Lab tests: Routine lab testing will be necessary to ensure the electrolytes are in balance.
  

Prognosis for Dogs With Addison's Disease

The prognosis for a dog with the disease is positive. Treatment is usually successful but your dog will likely need some sort of therapy long-term if not its entire life. However, your vet will also assess if your dog has signs of permanent kidney damage from the imbalances.

How to Prevent Addison's Disease

There is no way to prevent a dog from developing primary Addison's disease. Secondary Addison's may be avoidable by making sure your dog is carefully regulated while on any medications. Routine examinations can also help your veterinarian determine risk factors for secondary Addison's.

Early detection can make it easier to manage Addison's disease. Follow your vet's advice for routine lab work. Mild abnormalities may allow your vet to discover Addison's before your dog actually gets sick. Preventing an Addisonian crisis is the best way to keep your dog safe.