If your veterinarian diagnoses your dog with Canine Addison's disease, it is not an automatic death sentence. Once Addison's disease is confirmed, treatment is straightforward, and a dog with this condition stands as good a chance as any dog of living a normal life. Addison's disease appears to have some genetic properties and occurs in young to middle-aged dogs. It is more common in females than male dogs and in breeds such as Labrador Retrievers, Portuguese Water Dogs and Standard Poodles.
What Is Canine Addison's Disease?
Addison's disease is a disease of the adrenal glands. These small organs sit just in front of your dog's kidneys, with one on each side. Addison's disease, also called hypoadrenocorticism, results when the adrenal glands stop producing their normal products.
The adrenal glands have two layers, the adrenal cortex (outer layer), and the adrenal medulla (inner layer). The adrenal cortex is the portion involved with Addison's disease and can be divided into three additional layers:
- Zona glomerulosa which is the outer layer. It produces a hormone called aldosterone which regulates a complicated system of electrolytes and water balance.
- Zona fasciculata is the middle layer. It produces glucocorticoids such as cortisol, which help the body cope with stress.
- Zona reticularis which is the inner layer. It produces small amounts of sex hormones.
The adrenal medulla is not affected by Addison's disease and produces epinephrine (adrenaline).
Different Forms of Canine Addison's Disease
Several types of Addison's disease can develop in dogs, depending upon which layers of the adrenal glands are affected. The adrenal glands are partially controlled by the pituitary gland, often called the "master gland" which sits at the base of the brain. The pituitary gland has a lot of functions, but one of them is to secrete adrenocorticotropic hormone (ACTH). ACTH is released into the blood and travels to the adrenal glands. Once there, its main purpose is to tell the zona fasciculata layer of the adrenal glands to secrete cortisol.
Primary Addison's Disease
Primary Addison's disease is the most common form. This occurs when the adrenal glands stop functioning, independent of the pituitary gland. This is thought to occur as the result of an autoimmune problem with the adrenal glands. This form usually affects all the adrenal gland.
Secondary Addison's Disease
Secondary Addison's disease is rare and happens when the portion of the pituitary gland that produces ACTH stops functioning. If the body lacks ACTH, then the adrenal glands are never stimulated to produce cortisol. This type of Addison's disease only affects the zona fasciculata.
Atypical Addison's Disease
Atypical Addison's disease is almost the same as secondary Addison's disease. When Addison's disease only affects cortisol production, this is called atypical Addison's disease. Secondary Addison's disease is always atypical. Primary Addison's disease can be atypical in the early stages, but will progress to the regular form.
Iatrogenic Addison's Disease
The last type of Addison's disease is iatrogenic Addison's disease. This can occur as a result of medical treatment for Cushing's disease - a condition in which the adrenal glands are overactive. Medications used to suppress adrenal gland function can sometimes take the levels of adrenal hormones too low, resulting in Addison's disease. Also, dogs that are treated with long-term corticosteroid medications can have atrophy of their adrenal glands. If their medication is stopped suddenly, their adrenal glands cannot resume their normal functions quickly, and Addison's disease can result.
Summary of the Types of Addison's Disease
| Type of Addison's disease | Site of disease | Specific parts affected | Deficient hormones |
|---|---|---|---|
| Primary Addison's disease | Adrenal glands | Cortex - zona glomerulosa and zona fasciculata | Glucocorticoids and usually aldosterone |
| Secondary Addison's disease | Pituitary gland | Cortex - zona fasciculata | Glucocorticoids |
| Atypical Addison's disease | Pituitary gland or adrenal glands | Cortex - zona fasciculata | Glucocorticoids |
| Iatrogenic Addison's disease | Adrenal glands | Cortex - zona glomerulosa and zona fasciculata | Glucocorticoids and usually aldosterone |
Symptoms of Canine Addison's Disease
Addison's disease has been called the Great Imitator because the symptoms can be vague and may mirror several other diseases. Symptoms can occur suddenly, gradually, or can show up intermittently. Some of the symptoms of Addison's disease include:
- Vomiting
- Diarrhea
- Lethargy or listlessness
If canine Addison's disease is not identified, it can eventually result in an emergency called an Addisonian crisis. Symptoms of an Addisonian crisis include:
- Weakness and collapse
- Shock
- Seizures
- Bloody vomiting or diarrhea
- Low body temperature
Diagnosing Canine Addison's Disease
Diagnosis of canine Addison's disease is straightforward once the condition is suspected. However, because it is an uncommon illness and has vague symptoms, it may not be the first thing that your veterinarian thinks to check for, especially with rare forms (atypical or secondary Addison's disease).
Blood Testing
The first evidence of Addison's disease is usually found in blood testing. Dogs with primary Addison's disease usually have a low sodium level, high potassium level, and sometimes a low chloride level. The ratio of the sodium to potassium levels is often calculated to help assess the risk of Addison's disease. Anemia or a lack of stress-related changes in the blood cells can also be found. Elevated kidney values, elevated phosphorus, and a low blood sugar are also common in Addison's disease.
If your dog isn't very sick, your vet may run a blood cortisol test to screen for Addison's disease. If the test shows normal levels of cortisol, then your dog almost certainly does not have Addison's disease.
ACTH Stimulation Test
The definitive test for canine Addison's disease is the ACTH stimulation test. This can be a more expensive test and usually has to be sent to an outside laboratory, so it is not always done right away. In this test, a blood sample is taken from your dog, and then an injection of ACTH is given. A follow-up blood sample is taken two hours after the first one. If the test result shows low levels in both samples, this means that your dog has Addison's disease.
For secondary or atypical Addison's disease, more complicated testing is needed. Your vet may refer you to a specialist in this situation.
Treatment for Canine Addison's Disease
To treat Addison's disease, your dog will need to be on medication for the rest of his life. Your veterinarian will determine which protocol is best for your dog. Some of the possible medications include:
- Percorten-V™ (desoxycorticosterone pivalate or DOCP) - an injection that regulates water and electrolyte balance in place of aldosterone. This is given every 25 days, but the timing can change, depending upon your dog's bloodwork results.
- Florinef™ (fludrocortisone) - an oral medication that also works in place of aldosterone.
- Prednisone or prednisolone - an oral corticosteroid medication that replaces cortisol. The dose of this medication may need to be increased if your pet is stressed or ill.
If your dog suffers from an Addisonian crisis, hospitalization is needed. This is a dangerous medical condition, but most dogs respond quickly to treatment. For many dogs with Addison's disease, the initial diagnosis is made at the time of an Addisonian crisis.
Dogs with Addison's disease will require follow-up bloodwork to make sure that their doses of medication are correct. Make sure your dog gets his medication on schedule and communicate any concerns to your vet.
A Long, Happy Life
Will your dog be able to live a happy, healthy life with Addison's disease? Yes, once the diagnosis is made, dogs with this disease have a good prognosis and can live a normal lifespan.
