Sunday, April 3, 2011

Addison’s Disease in Dogs: A Life-Threatening Disorder

Addison’s disease, also called hypoadrenocorticism, is a disorder in which the adrenal gland does not produce sufficient hormones. The adrenal glands are essential for life. When the adrenal gland fail, the consequences are very severe.

What are the missing hormones in Addison's disease?
Dogs with hypoadrenocorticism (Addison's disease) are unable to produce one or two steroid hormones, both secreted from the adrenal cortex (outer layer of the adrenal gland).
  1. The first hormone that's missing is cortisol, which is very important in maintaining a normal metabolism, as well as a general sense of well being.
  2. The second hormone that's missing is aldosterone, which manages the water balance and serum electrolytes in the body.
What are the different forms of hypoadrenocorticism?
Hypoadrenocorticism can be divided into primary and secondary subtypes. A third form, called "atypical" Addison's disease appears to be an early stage of primary hypoadrenocorticism in most dogs.
  • With primary hypoadrenocorticism (Addison's disease), the problem lies in the adrenal gland itself, with atrophy or destruction of the gland.
  • With secondary hypoadrenocorticism, the adrenal gland are normal, and the problem lies in the pituitary gland. The pituitary gland normally secretes a hormone called ACTH (adrenocorticotropic hormone) that stimulates the adrenal gland to secrete its hormones; in secondary hypoadrenocorticism, ACTH is not secreted in needed amounts, leading to the secondary adrenal insufficiency.
  • The third subtype, atypical Addison's disease appears to be an early stage of primary hypoadrenocorticism in which only part of the adrenal gland has been completely destroyed.
What causes Addison's disease in dogs?
In most dogs, we cannot determine what caused their adrenal disease. With primary hypoadrenocorticism, the following causes must be considered.
  • Most dogs with the primary form appear to have an autoimmune condition in which the body destroys part of the adrenal cortex
  • Very rarely, infiltrative conditions such as cancer can metastasis to and destroy the adrenal gland to cause Addison’s disease
  • Occasionally, treatment of Cushing’s disease with the drugs mitotane and trilostane will result in complete adrenal destruction and Addison’s disease
With secondary hypoadrenocorticism, we must rule out the following underlying causes.
  • Congenital deficiency of ACTH secretion
  • Pituitary tumors, inflammation or trauma that have destroyed most of the ACTH-secreting cells in the pituitary gland, leading to deficient ACTH secretion
With atypical hypoadrenocorticism:
  • The mechanism by which atypical Addison's disease develops in not well-understood
  • Most of these dogs appear to have an early stage of primary hypoadrenocorticism
  • In these dogs, destruction of the adrenal cortex is not complete, making diagnosis more difficult
Are some dogs predisposed to developing this disease?
Although hypoadrenocorticism can develop in any age, breed, or sex of dogs, the following points should be taken into consideration when making a diagnosis.
  • Hypoadrenocorticism is most common in young to middle-aged dogs.
  • Most dogs with Addison's disease are females.
  • Bearded Collies, Standard Poodles (see photo on left, below) , Great Danes, Portuguese Water Dogs, West Highland White Terriers (see photo on right, below), and Leonbergers are all predisposed to developing this disease.
Chain of events leading to severe hypoadrenocorticism in dogs
With primary hypoadrenocorticism (Addison's disease), the dog generally develops complete adrenocortical destruction with both cortisol and aldosterone deficiencies.

Aldosterone is the main mineralocorticoid hormone, and it affects the levels of potassium, sodium, and chloride in the blood. Low levels of aldosterone cause potassium to gradually build up in the blood and, in severe cases, cause the heart to slow down or beat irregularly. Some dogs have such a slow heart rate (50 beats per minute or lower) that they can become weak or go into shock.

Less commonly, dogs will develop secondary or "atypical” primary hypoadrenocorticism. This subgroup of dogs are only deficient in cortisol and appear to maintain a normal aldosterone level, at least early in the course of their disease. These dogs are more difficult to diagnose because their signs are milder and the serum potassium, sodium, and chloride values all remain normal.

Clinical features of hypoadrenocorticism in dogs
Historically, hypoadrenocorticism generally has a waxing and waning course and may be confused with other diseases because the clinical signs are not specific. The most common clinical signs and physical exam finding include the following:
  • Depression or lethargy
  • Weakness or collapse
  • Anorexia (poor appetite)
  • Weight loss
  • Vomiting or diarrhea
  • Excessive thirst and urination
  • Hypothermia (low body temperature)
  • Dehydration and shock
Signs of Addison’s disease include repeated episodes of vomiting and diarrhea, loss of appetite, dehydration, and gradual, but severe, weight loss. Because the clinical signs of Addison’s disease are vague and nonspecific, it can be difficult to diagnose in the earlier stages of disease. Therefore, severe consequences, such as shock and evidence of kidney failure, can develop suddenly in some dogs.

In my next post, I'll discuss how we can diagnose hypoadrenocorticism, can will be fatal if not properly managed.


Elaine Johnson said...

My 7 year old Springer Spaniel has been diagnosed with Addison's by my vet. We are monitoring her carefully and the administration of Percoten is being given as well as steroids ( cortisol ). I am concerned about the anemia. Her weight has remained steady. She is constantly thirsty and I am carefully monitoring that as the elimination is a constant problem. Many household accidents and I do need to sleep!
Are there any other things I need to know. Your article is very informative.

Dr. Mark E. Peterson said...

Anemia can develop as part of Addison's disease, but that should resolve within 2-3 months of replacement therapy. Dogs with Addison's should not be drinking or urinating more than a normal dog. In most of these dogs, increased thirst means that you are giving too much cortisol replacement therapy.

Talk to your vet about the dose and if it can be lowered (most dogs only need 0.1 mg/kg of prednisone each day).

James Weir said...

My 6 yo springer recently developed symptoms: lethargy, no Appetite etc. the vet was suspicious of addisons and because it was the weekend, started treatment right away with Fludrocortisone. After the first dose there was a noticible difference. We haven't actually tested him yet and to do that will require him off meds for 5 days. Wondering if it is safe to do that or should we just assume he has it and continue treatment?

Dr. Mark E. Peterson said...

Why would one treat a dog life-long for a disease he/she didn't have? Of course you need to make a proper diagnosis.

Callie said...

I have pre drawn up percorten inj for my dog and I just gave him his inj IV & forgot to thump the syringe to mix everything. Will he be ok? I have of course texted my vet to ask but he hasn't responded yet & I'm a little freaked out!

Dr. Mark E. Peterson said...

If you mixed up the bottle of the suspension well before you drew it up into the syringe, and then gave it shortly thereafter, you should be fine.