Addison's Disease in Dogs

What is Addison's Disease?

Addison’s disease (hypoadrenocorticism) is caused by a lower than normal production of hormones, such as cortisol, by the adrenal glands. The adrenals are small glands that are located near the kidneys. Adrenal hormones are necessary to control salt, sugar and water balance in the body. Addison’s disease occurs less commonly than the opposite condition, Cushing’s disease (overproduction of cortisol) in dogs, and is rare in cats. 

Addison’s disease occurs most commonly in young to middle-aged female dogs. The average age is about 4 years old.  The signs of Addison’s disease may be severe and appear suddenly, or may occur intermittently and vary in severity.

Signs may include:

• Weakness
• Depression
• Lack of or loss of appetite
• Vomiting
• Diarrhea
• Occasionally increased thirst (polydipsia)
• Increased urine production (polyuria).

When a pet is stressed, their adrenal glands produce more cortisol, which helps them deal with the stress. Because dogs with Addison’s disease cannot make enough cortisol, they cannot deal with stress, so the signs may occur or worsen when stressed. What a dog finds stressful depends upon his/her temperament. For many dogs, any change in their day-to-day routine, such as being boarded or having house guests, is stressful and may precipitate or worsen signs of Addison’s disease.

On examination of dogs with Addison’s disease one may see:

• Depression
• Weakness
• Dehydration
• Weak pulse and sometimes a slow, irregular heart rate. 
• Some dogs with Addison’s disease have low blood sugar
• Routine laboratory tests often show a low blood sodium and high blood potassium.
• The urine is often diluted. Sick dogs often show a pattern of changes in their white blood cells (WBCs) called a stress leukogram. This pattern of changes in the WBCs is caused by cortisol. The absence of a stress leukogram in a sick dog may be a clue to consider Addison’s disease.
• Loss of water, in vomit and diarrhea, can lead to dehydration. Severe dehydration increases waste products in the blood (creatinine and blood urea nitrogen = BUN) that are normally eliminated by the kidneys. Addison’s disease can sometimes be confused with primary kidney disease.  

Increased blood potassium can cause life-threatening abnormalities in the heart rhythm. These abnormalities can cause the heart rate to be slow and irregular and can be seen on an electrocardiogram (ECG). 

X-rays of dogs with Addison’s disease do not show any specific abnormalities. The heart may appear smaller than normal and on rare occassions the esophagus (tube from mouth to stomach) can be enlarged.

The history, physical examination, and initial laboratory tests provide suspicion for Addison’s disease, but a more specific test, an ACTH challenge, should be performed to confirm the disease . 

There are two stages of treatment for Addison’s disease; in-hospital treatment and long term treatment. Very sick dogs with Addison’s disease require intravenous fluids, cortisol-like drugs and additional drugs to neutralize the effects of potassium on the heart. 

Long-term treatment involves the administration of hormones in one of two forms; either a daily pill or a shot that is given about every 25 days. Because dogs with Addison’s disease cannot produce more cortisol in response to stress, stress should be minimized whenever possible. It may be necessary to increase the amount of hormones given during periods of stress (e.g. boarding, surgery, travel, etc.). 

With appropriate treatment for Addison’s disease, dogs can live a long and happy life.