Canine Hypoadrenocorticism / Addison’s Disease in Dogs
Oversimplified, Addison’s Disease occurs when the adrenal glands don’t release adequate amounts of two hormones that regulate critical body functions. Symptoms of Addison’s Disease are many — increased thirst and urination, vomiting, diarrhea, weakness, no appetite, shaking or shivering, abdominal pain, weak pulse, slow heart rate. Once diagnosed, dogs with Addison’s Disease must receive hormone therapy for life.
Addison’s disease or hypoadrenocorticism is an uncommon disease of dogs involving the adrenal glands.
Glucocorticoids (primarily cortisol) and mineralocorticoids are two important types of hormones produced by the body’s adrenal glands. Under normal conditions, the brain releases a hormone called adrenocorticotropic hormone (ACTH) that stimulates the adrenal glands to release their hormones.
Addison’s disease occurs when the brain doesn’t release adequate amounts of ACTH or the adrenal glands fail to release their hormones in response to ACTH.
Glucocorticoids and mineralocorticoids help regulate numerous complex processes in the body and participate in critical functions such as:
- Maintaining the body’s fluid balance
- Maintaining the body’s balance of sodium and potassium
- Maintaining the integrity and functioning of blood vessels
- Regulating blood pressure and blood flow to vital organs, like the kidneys
- Supporting cardiac function
- Controlling blood sugar levels and carbohydrate metabolism
- Helping counteract the effects of stress
- Helping maintain immune system function
In most cases, the cause of Addison’s disease is not determined. Sometimes, the body’s immune system can damage the adrenal glands’ cells so extensively that they can’t release hormones when they need to. In other cases, such as a brain tumor, the part of the brain that should release ACTH is unable to. However, Addison’s disease can also occur if a pet that is receiving cortisol medication suddenly stops getting it. In this case, the body has reduced its own cortisol production and can’t increase it quickly enough to compensate when the medication is discontinued. This is why steroid medications (such as prednisone) should not be discontinued suddenly, but must instead be gradually reduced and then discontinued.
Addison’s disease is most commonly diagnosed in dogs, although it does occur rarely in cats. Young to middle-aged dogs are generally affected, and females are more commonly affected than males.
Symptoms and Identification
Because adrenal gland hormones are instrumental in a wide variety of the body’s basic functions, symptoms of Addison’s disease can resemble those of other illnesses. Increased thirst and urination, vomiting, diarrhea, depression, weakness, loss of appetite, shaking or shivering, weight loss, abdominal pain, weak pulse, slow heart rate, and even collapse can result. Signs will often appear or worsen during periods of stress. They can be constant or episodic, mild or severe, and (if subtle) may go unnoticed.
Diagnosis of Addison’s disease may require several steps, but results of initial diagnostic tests can help support a diagnosis. The following tests are usually undertaken:
- Blood tests, including a chemistry panel and complete blood cell count (CBC)
- Abdominal radiographs (X-rays)
- Abdominal ultrasonography
- In dogs with Addison’s disease, initial blood tests may include the following abnormalities:
- Low sodium levels
- High potassium levels
If your veterinarian suspects Addison’s disease, an additional test called an ACTH stimulation test may be recommended. As described above, ACTH is the hormone the brain produces that stimulates the adrenal glands to release glucocorticoids and mineralocorticoids. In a dog with Addison’s disease, ACTH may be absent or the adrenal glands may be unable to respond adequately to it. The ACTH stimulation test involves administering a small amount of ACTH by injection and then measuring the levels of cortisol produced over a period of a few hours. In dogs with Addison’s disease, the injection of ACTH does not result in a significant increase in cortisol levels. This response can be used to confirm a diagnosis.
The ACTH stimulation test requires a few hours of hospitalization so that blood can be drawn to check the body’s response to the injection.
Addison’s disease can affect dogs of any breed, including mixed breed dogs. Some breeds, including toy and standard poodles, Labrador retrievers, Great Danes, Rottweilers, and West Highland white terriers seem to have a higher incidence of the disease.
Some animals are seriously ill by the time the disease is diagnosed, usually when they suffer what is known as acute adrenocortical insufficiency (“Addisonian crisis”). Low blood pressure, dehydration, impaired heart function, and other complications of the disease can be fatal if not treated immediately and aggressively. In such a case, hospitalization for emergency intravenous fluid therapy and other stabilization is necessary.
In other cases, the clinical signs of Addison’s disease are more subtle. As long as the dog is stable, outpatient treatment can begin.
The primary treatment for Addison’s disease consists of giving the body the adrenal gland hormones it’s been unable to produce on its own. Glucocorticoid supplementation commonly involves administering prednisone or hydrocortisone pills. Most dogs also need mineralocorticoid supplementation; these are available in pill and injectable formulations. A popular mineralocorticoid formulation is injectable deoxycorticosterone pivalate (DOCP); this medication can be given as an injection every 21 to 30 days.
Medications for Addison’s disease only replace missing hormones; they don’t cure the disease. Therefore, dogs with Addison’s disease need to receive medications for the rest of their lives. Periodic veterinary examinations and repeat blood testing are required for the life of the pet, and sometimes medication dosages need to be adjusted. Your veterinarian may also want to discuss modifying your pet’s medication during times of stress, when the body’s need for these hormones may increase. Fortunately, dogs that receive proper treatment for Addison’s disease can have normal life spans and enjoy a good quality of life.
This article was reviewed by a Veterinarian.