Summary
Addison's disease or hypoadrenocorticism is an uncommon disease of dogs in which the adrenal glands' outer layer (the cortex) is destroyed. In most cases, it's the body's own immune system that leads to the destruction of this sensitive endocrine tissue, which leads directly to a decrease in the production of two classes of hormones: glucocorticoids and mineralocorticoids.
Cancers and certain drugs can also affect a breakdown in the adrenal glands' cortex. In all cases, both adrenal glands are affected.
Young, female dogs of certain breeds are predisposed, therefore suggesting a genetic origin. A mode of inheritance has not yet been established.
Symptoms and Identification
Because both these hormone classes are instrumental in a wide variety of the body's basic functions, symptoms are typically non-specific. Increased thirst and urination, vomiting, diarrhea, depression, weakness, loss of appetite, shaking or shivering, and even collapse can result. Signs will often appear or worsen during periods of stress. Symptoms can be constant or episodic, mild or severe and all or none of the above symptoms may be in evidence.
Vague as the signs of Addison's typically are, diagnosis can be difficult to achieve. While screening tests (bloodwork) can sometimes help identify Addison's in advance of obvious or severe symptoms, few cases are identified routinely.
In Addisonian patients, lab work typically reveals low sodium levels, high potassium levels, low chloride levels, anemia, dehydration and high calcium levels.
A blood test designed to challenge the adrenal gland into producing cortisol is used to achieve a definitive diagnosis (ACTH stimulation test). An EKG may also reveal changes associated with high potassium levels.
Affected Breeds
Addison's disease appears to be more prevalent in the following breeds:
Standard Poodle; Labrador Retriever; Nova Scotia Duck Tolling Retriever; Portuguese Water Spaniel; Great Dane; Rottweiler; Soft-Coated Wheaten Terrier; and West Highland White Terrier
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 by the destruction of the adrenal glands' cortical tissue.
Veterinary Cost
The cost of diagnosis can be inexpensive or not, depending on the degree to which the dog's symptoms confound the diagnostic process and based on the number of affiliated problems a dog may concurrently experience. $500 to $1,500 is considered typical for a complete diagnosis (though the low end of this estimate would not include an ultrasound).
Dogs with a requirement for intensive care during the diagnostic process will invariably amass higher veterinary bills. Bills totaling thousands of dollars might be reasonably expected in some atypical instances.
Medical treatment can be as low as $50 a month or as high as $200, depending on the dog's response to treatment and the drug(s) selected. Frequent lab work must also be factored in to the cost structure to ensure that patients are responding appropriately.
Prevention
There is no known means of prevention save genetic counseling which would serve to eliminate affected dogs and their first degree relatives from the breeding pool.
References
Kintzer, PP and Peterson, ME. 1995. Hypoadrenocorticism in dogs. In JD Bonagura and R Kirk (eds) Kirk's Current Veterinary Therapy XII Small Animal Practice. p 425-429. WB Saunders Co. , Toronto.