Typical and Atypical Addison's Disease in Dogs
Addison Disease in Dogs: "The Great Pretender"
Addison’s disease in dogs, otherwise known as hypoadrenocorticism, is a condition that occurs when a dog's adrenal glands no longer work as they should. In a healthy dog, well-functioning adrenal glands are responsible for producing the important hormones cortisol (a hormone that plays a role in a dog's ability to manage stress and regulate glucose) and aldosterone (a hormone responsible for maintaining proper hydration and correct electrolyte/mineral balance.)
When the adrenal glands no longer work as they should, these hormones aren't secreted at normal levels. In many cases, the glands fail to work properly as a result of damage caused by the immune system. While the immune system is responsible for keeping dogs and people healthy, a time may come where for unknown reasons, it ends up attacking and damaging its own tissues.
Addison's disease is often nicknamed "the great pretender." This condition is known for causing vague, intermittent symptoms that may come and go, vary in intensity, and may mimic several other conditions. This condition is frequently misdiagnosed and causes loss of time, frustration, and general risks. Left untreated, the disease may progress to what is known as an Addisonian crisis, which may quickly turn life-threatening if not treated promptly.
What Are the Symptoms?
- Loss of appetite
- Increased drinking
- Increased urination
When it comes to statistics, this condition has a strong preference for female dogs. It is estimated that 70% of dogs diagnosed with Addison's disease are female. Although it may affect dogs of any sex or age, there is a high prevalence in young to middle-aged dogs, generally between the ages of 4 to 7 years old.
What Breeds Are Predisposed?
Although any dog breed may get Addison's, some dog breeds appear to be more predisposed:
- Great Danes
- Border Collies
- Portuguese Water Dog
Although the disease can turn life-threatening, the good news is that once discovered, it can be managed fairly easily. Treatment of Addison's disease in dogs varies based on whether you are dealing with typical or atypical Addison's disease in dogs.
Did You Know?
Different parts of the adrenal glands secrete different things. The zona glomerulosa secretes aldosterone, which helps in the regulation of salt. The zona fasciculata secretes cortisol, which helps regulate sugar. The zona reticularis secretes androgens which convert to sex hormones.
Typical Addison's Disease in Dogs
In dogs suffering from typical Addison's disease (also known as primary Addison's disease), the middle and outer layers of the dog's adrenal glands are typically damaged which leads to both cortisol (glucocorticoids) and aldosterone hormones (mineralocorticoids) not being produced in sufficient amounts.
When dogs with undiagnosed typical Addison's disease undergo blood tests that include checking the dog's electrolyte levels, their sodium and potassium levels are generally off the charts. They will have elevated BUN and creatinine levels and mild to moderate anemia, which often prompts veterinarians to consider testing for a definite diagnosis through what's called an ACTH test.
Dogs with typical Addison's disease do not produce sufficient amounts of cortisol and aldosterone, so treatment consists of replacing these hormones with corticosteroid drugs and electrolyte replacement drugs such as Florinef.
In most cases, canine Addison's disease, or primary hypoadrenocorticism, is likely caused by immune-mediated destruction of adrenal tissue in response to an unknown trigger, resulting in primary adrenocortical failure with glucocorticoid (cortisol) and mineralocorticoid (aldosterone) insufficiency.— Dr. David S. Bruyette, board-certified veterinarian specializin in internal medicine.
Atypical Addison's Disease in Dogs
Sometimes, only the middle layer of the dog's adrenal glands is damaged, which allows the dog's adrenal glands to produce the electrolyte balancing hormone aldosterone, but not cortisone. If only the middle layer fails, meaning the adrenals are still producing electrolyte balancing hormones, the condition is known as atypical Addison's disease.
Atypical Addison's disease in dogs is challenging at times to diagnose. The fact is, affected dogs' routine blood work doesn't provide any hints such as the abnormalities often detected in the typical type. There are no abnormal levels of sodium, chloride, and potassium levels or other significant abnormalities.
Since dogs with the atypical type are glucocorticoid deficient, their main treatment consists of prednisone. Once therapy is implemented, affected dogs should quickly recover, feel better, return to eating and drinking, and gain back weight. Dog owners must consider providing larger doses of prednisone as needed when their dogs are likely to encounter periods of physical or medical stress.
Most patients with atypical Addison's disease are not mineralocorticoid-deficient and maintain normal sodium/potassium ratios throughout their lives.— Jennifer E. Waldrop, Diplomate” of the American College of Veterinary Emergency and Critical Care
Key Points to Remember About the Disease
- Typical Addison's disease causes dogs to lose function of the entire adrenal cortex; in atypical cases, only certain portions are affected.
- Glucocorticoid deficiency (lowered cortisol levels), which is the most common form of the atypical type, accounts for up to 45% of all Addison's cases.
- Dogs with the atypical type tend to not be mineralocorticoid-deficient and tend to have normal sodium/potassium ratios in their bloodwork.
- Dogs who have cortisol levels below 2.0 should be tested for Atypical Addison's.
- Dogs with typical Addison's need prednisone to replace cortisol, and Percorten, Zycortal, or Florinef to balance their electrolytes since they do not make aldosterone. Atypical dogs need only prednisone to replace cortisol.
- On top of the typical and the atypical form, there is a third form called Secondary Addison's disease. This type occurs due to a lack of ACTH secretion from the pituitary gland. The condition is usually iatrogenic (inadvertently induced by medical treatment) and takes place from abruptly discontinuing long-term administration of glucocorticoids without tapering off.
Resting cortisol concentration is a great way to rule OUT Addison's disease. If the resting cortisol concentration is > 2 µg/dl, then the patient is not likely to be addisonian. In cases with a resting cortisol < 2 µg/dl, you must perform an ACTH stimulation test to confirm the disease.— DVM360
- Ettinger SJ, Feldman EC. Textbook of veterinary internal medicine, 6th ed. St. Louis, Mo: Saunders Elsevier, 2005;1619.
- J Vet Intern Med. 2014 Sep-Oct;28(5):1541-5. doi: 10.1111/jvim.12415. Epub 2014 Jul 28. Basal serum cortisol concentration as a screening test for hypoadrenocorticism in dogs. Bovens C1, Tennant K, Reeve J, Murphy KF
- Sadek D, Schaer M. Atypical Addison's disease in the dog: a retrospective survey of 14 cases. J Am Anim Hosp Assoc 1996;32(2):159-163.
This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.