To understand canine Addison’s Disease (Hypoadrenocorticism), we need to first understand the functions of the adrenal glands.
The adrenal glands are located in the dog’s abdomen just above the kidneys.
The glands are made up of two distinct layers.
The interior layer (called the medulla) is responsible for producing hormones similar to adrenaline.
The outer layer (called the cortex) is responsible for producing corticosteroids, which are hormones that enable animals to adapt to stress physiologically.
Corticosteroids are divided into two groups: glucocorticoids and mineralocorticoids.
Glucocorticoids regulate protein, carbohydrate, and fat metabolism. In a fight-or-flight situation, they help get the body ready to burn fuel for energy.
Mineralocorticoids regulate electrolyte balances – sodium and potassium. In a fight-or-flight situation, sodium is conserved in preparation for possibility of blood loss. As sodium is conserved, potassium is lost as a result.
In short, corticosteroid hormones are essential for animals to physically adapt and adjust to situations that are stressful. Without these hormones, even a small stressful situation could result in serious physical damage.
What is Canine Addisons Disease
Addison’s disease in dogs is caused by the inability of the adrenal glands to produce enough glucocorticoidss and mineralocorticoids.
Specially, in Addison’s disease, the two hormones that are most commonly deficient are cortisol (part of the glucocorticoid group of hormones) and aldosterone (part of the mineralocorticoid group of hormones).
Cortisol helps the dog’s body deal with stress, converses food into energy, and manages the immune system’s inflammatory response. Aldosterone helps maintain proper blood pressure, and allows the kidneys to keep a proper balance of sodium and potassium in the dog’s body.
Canine Addisons disease is the opposite of Cushing’s disease in dogs, in which the adrenal glands produce excessive corticosteroids.
Canine Addison’s disease occurs less commonly than Cushing’s disease, but it still occurs quite frequently in dogs, especially among young to middle-aged female dogs. The average age is about 4 years old.
There may be a genetic predisposition in Bearded Collies, Portuguese Water Dogs, and Standard Poodles.
Different Forms of Canine Addisons Disease
Addison’s disease in dogs come in three different forms. They are:
Primary Addison’s Disease
This form of Addison’s disease is an autoimmune disease and is by far the most common form. It is characterized by an abnormal response of the immune system which causes the dog’s body to attack its own tissue.
As a result, the adrenal glands are damaged and fail to produce sufficient corticosteroid hormones. A tumor of the adrenal gland can also cause primary Addison’s disease.
Secondary Addison’s Disease
This form of canine Addisons disease is caused by an insufficient amount of adrenocorticotropic hormone (ACTH) which is secreted by the pituitary gland. ACTH is a hormone that stimulates the adrenal gland to work.
A lack of ACTH therefore results in underworking of the adrenal glands and consequently a deficiency of the corticosteroid hormones.
Secondary Addison’s disease can also be caused by a reduced production of corticotropin releasing factor (CRF) by the hypothalamus. CRF is a hormone that controls the adrenal glands. Failure of the pituitary gland or hypothalamus is usually a result of a tumor, inflammation, or injury.
Atypical Addison’s Disease
Atypical Addison’s is similar to Primary Addison’s in that the adrenal glands are not working properly. In Atypical Addison’s, the adrenal glands fail to secrete the glucocorticoid hormones only. Therefore, generally speaking, dogs with Atypical Addison’s have normal electrolyte balances.
Symptoms of Canine Addisons Disease
The symptoms of canine Addisons disease are very vague. As a result, many dogs may have symptoms for a long time before the disease is diagnosed.
To make diagnosis even more difficult, many of the symptoms in Addison’s disease may wax and wane over a period of time.
Some of the more common symptoms include:
- Muscle weakness
- Appetite loss
- Vomiting and diarrhea
- Weak pulses and sometimes a slow, irregular heart rate
Beware of “Addisonian Crisis”
Sometimes Addison’s disease may manifest itself in an “Addisonian Crisis” in which the poor dog collapses in a state of shock due to an imbalance of electrolytes and metabolism during a period of stress.
This results in extremely low blood sugar and high potassium levels.
In addition, the dog’s heart rate slows down, and irregular heart beat (arrhythmias) may result. In some cases, a dog in an Addisonian crisis cannot survive.
Diagnosis and Treatment
A definitive diagnois can be made using a blood test called the ACTH stimulation test.
As mentioned above, the symptoms of canine Addisons disease are vague and varied. Therefore, generally, a series of other tests will have been done to rule out other causes before the ACTH test is being given.
In an ACTH test, the dog is given an injection of the adrenal stimulating hormone ACTH. In a normal healthy dog, the response will be an increase in blood cortisol.
In a dog with Addison’s disease, there will NOT be an increase in blood cortisol and the diagnosis of Addison’s disease is confirmed.
Dogs with Addison’s disease require in-hospital treatment and long-term treatment.
Dogs who are very sick with severe symptoms need to be hospitalized. They receive intensive treatment which includes intravenous fluids, cortisol-like drugs, and drugs that neutralize the effects of potassium on the heart.
Long-term treatment involves replacing the mineralocorticoids and glucocorticoids in the body. This can be done by giving the dog hormones either orally or by injection, about every 25 days.
The oral form of medication most commonly used is Florinef (fludrocortisone). Florinef is usually given twice a day.
The injection type of drug is called DOCP. DOCP has been tested widely and intensively; it has been proven to give better electrolyte regulation than Florinef.
A small, maintenance dose of prednisone may also be given to some dogs being treated with DOCP.
Dogs with canine Addisons disease are unable to produce extra cortisol in response to stress, so if your dog is suffering from this disease, try not to expose him to stress if possible. The dog may need an extra amount of hormones during periods of stress (e.g. boarding, surgery, etc.).