Canine Addison’s Disease

Addison’s disease, clinically known as Hypoadrenocorticism (HOAC) is an uncommon disease seen in small animal practice. This condition is a hormonal disorder that is caused by a deficient production of the adrenal gland hormones, cortisol and aldosterone.

Early warning signs are often overlooked because they are mild and tend to come and go without treatment, but as a pattern of symptoms develops.

Sometimes this condition takes on a much more serious presentation resulting in sudden weakness, with severe vomiting and diarrhea, and sometimes collapse. This is an Addisonian crisis and is considered a medical emergency. Immediate hospitalization and supportive treatment are needed.

Addison’s disease in dogs occurs most frequently in young to middle-aged female dogs but has been diagnosed in dogs of all ages and either sex (including neutered animals).

Certain breeds seem to be at increased risk for developing Addison’s disease. These include, but are not limited to: Portuguese Water Dogs, Bearded Collies, Standard Poodles, Nova Scotia Duck Tolling Retrievers, Leonbergers, Great Danes, and Labrador Retrievers.

Types of Addison’s Disease

There are two types of Addison’s disease, referred to as primary and secondary Addison’s disease.

Primary Type Addison’s Disease

Primary Addison’s disease is the most common form; it may be futher subdivided into typical and atypical disease. The primary type of Addison’s is a result of your dog’s own immune system destroying the adrenal gland itself. Why this happens is unknown (idiopathic). Certain medications, toxins, cancer, or concurrent disease are less common causes of primary hypoadrenocorticism.

Addison’s disease may also result when the drug used to treat Cushing’s syndrome destroys too much of the adrenal tissues, resulting in a deficiency of cortisol and aldosterone.

Secondary Type Addison’s Disease

Secondary Addison’s disease results from a problem, such as a tumor, in the pituitary gland, which is an important hormonal regulator located in the brain. This disease can also develop if your dog has been treated with long-term steroids for any reason and the medication is abruptly stopped

Causes of Canine Addison’s Disease

The onset of Addison’s disease is usually the result of some destructive process affecting both adrenal glands and the cells that produce both of these critically important hormones. The most common cause of Addison’s disease is destruction of both adrenal glands by the individual’s own immune system.

For reasons that are not well understood, the immune system occasionally sees normal body parts as “foreign” and sets out to kill these tissues. In this uncommon instance, the immune system sees the adrenal glands as foreign and kills these cells.

Less common causes of Addison’s disease are cancers or infections that can invade and kill the adrenal glands.

Symptoms of Addison’s Disease in Dogs

Reduction in the production of aldosterone and cortisol causes the symptoms that pet owners and veterinarians most commonly see with the disease.

Symptoms Include:

• Depression
• Lethargy
• Anorexia (lack of appetite)
• Weight loss
• Vomiting
• Diarrhea
• Bloody stools
• Alopecia (hair loss)
• Increased urination
• Increased thirst
• Dehydration
• Shaking
• Weak pulse
• Irregular heart rate
• Low temperature
• Painful abdomen
• Hypoglycemia
• Hyperpigmentation of the skin

Treatment

Most animals are seriously ill by the time the disease is diagnosed, usually when they suffer what is known as acute adrenocortical insufficiency (“Addisonian crisis”).

Because the dehydration and electrolyte imbalances that accompany Addison’s disease can be very severe at the time of presentation. Intensive care involving fluid therapy and corticosteroids, among other stabilizing drugs, is often required to correct these aberrations and reverse the dog’s symptoms.

Long term, treatment is undertaken through drug therapy designed to replace the hormones lost. This is to destroy of the adrenal glands’ cortical tissue.