Also known as hypoadrenocorticism or adrenal insufficiency, Addison’s disease is a medical condition affecting the dog’s adrenal glands. Unlike Cushing’s disease, where the adrenal glands produce too much cortisol, in Addison’s disease the adrenal glands produce less corticosteroid hormones than needed. Fortunately, it is less common than Cushing’s disease. In order to better understand this form of endocrine disease, it’s worthy to better understand how the adrenal glands in a healthy dog work and how to recognize signs of trouble.
Understanding the Role of the Adrenal Glands
The adrenal glands are very small glands that sit just above the dog’s kidneys. These glands are known as endocrine glands, meaning that they release hormones directly into the bloodstream. In particular, adrenal glands are responsible for producing two important hormones that are secreted in times of stress. These hormones are epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline.) The adrenal glands are also important for producing important mineralocorticoids such as aldosterone which ensures the dog’s electrolytes are in balance by regulating the secretion of potassium and the retention of sodium. Last but not least, the glands also produce the sex hormones testosterone and estrogen.
In a healthy dog, when the adrenal glands work well, the dog’s body responds well to stress and his potassium and sodium levels are well balanced. No apparent signs of trouble are present. Problems start when insufficient mineralocorticoids are produced and the dog develops Addison’s disease which causes loss of sodium and the retention of potassium which can have devastating physiological effects.
Causes
What causes a dog’s adrenal glands to not function as they are supposed to? There are various explanations. Because this condition is seen more in certain breeds, there seems to be a genetic factor involved. Primary and secondary forms of this disease exist. In the primary form the adrenal glands are the main culprit. An infection of the presence of a tumor on these glands may interfere with their proper functioning. In some cases, autoimmune disorders may cause the dog’s immune system to attack and damage the adrenal gland’s tissue. In several instances, the underlying cause remains unknown, which is why this condition is often labeled as “idiopathic.”
In the secondary form of Addison’s disease, the condition is triggered by failure of the pituitary gland to stimulate the adrenal glands with adrenocorticotropic hormone (ACTH). In some cases, the onset is triggered by the sudden withdrawal of steroids that have been administered for some time. The adrenal glands in this medically-induced form of Addison may have atrophied from lack of stimulation leading to a deficiency in glucocorticoids. To avoid this from happening, steroids should always be gradually tapered off.
Symptoms
Affected dogs often present to the vet with vague symptoms that often wax and wane. The symptoms are often categorized under the “Ain’t doing right” category. In several cases dogs may be misdiagnosed. For a good reason this disease is often referred to as the “great imitator” as it can mimic other disorders. Stressful events such as boarding may trigger an escalation in symptoms. In severe cases, the imbalance of electrolytes may cause what is known as an “Addisonian crisis” which causes shock, collapse and even death if left untreated. Common symptoms typical of are as follows:
- Vomiting and diarrhea
- Weight loss
- Frequent drinking
- Frequent urination
- Dehydration
- Loss of appetite
- Lethargy
- Pain in the hind quarters
- Lower heart rate
- Weak pulse
- Low body temperature
- Inability to stand
- Tremors
- Shock
- Collapse
Which Dogs are Affected the Most?
It is estimated that 40 to 85 % of dogs affected by Addison’s disease are female, middle-aged dogs, generally between the ages of 4 and 7. There are some dog breeds which seem to be predisposed to developing it. Great Danes, Portuguese water dogs, Chinese crested dogs, Rottweilers, standard poodles, West highland and soft coated wheaten terriers are a few.
Diagnosis
As mentioned, this disease causes symptoms that are quite similar to others, which makes an accurate diagnosis on the challenging side. Clinical presentation alone won’t suffix to generate a diagnosis. Several tests may need to be run to rule out other more common disorders. Bloodwork sometimes reveals low sodium and high potassium levels, but not always. High levels of BUN and creatinine are often seen causing some vets to suspect kidney failure. An ECG may reveal heart rhythm abnormalities. The most revealing test is the ACTH stimulation test. In a healthy dog, the injection of adrenal-stimulating hormones triggers the adrenal glands to cause cortisol levels to rise; whereas, in a dog with Addison disease, the adrenal glands won’t respond, and therefore, the cortisol levels will not rise. This lack of response along with the exclusion of other disorders is the ultimate diagnostic proof.
Treatment
Luckily, Addison’s disease can be managed, allowing dogs with this condition to lead quite normal, active lives. Treatment varies depending on the underlying cause. In the case of primary Addison’s disease, dogs are often prescribed fludrocortisone acetate (Florinef) or an injectable drug called Percorten V which is given every 25 days. These drugs are meant to replace aldosterone, and therefore, help maintain the dog’s levels of sodium and potassium. Cases of secondary Addison are treated with glucocorticoids. Because dogs suffering from this condition cannot produce sufficient cortisol in the face of stress, avoidance of stress is very important. When stressful events happen, it’s important to supplement these dogs with glucocorticoids. All owners of dogs with this disease should keep some prednisolone handy just in case.
An Addisonian crisis must be treated promptly through the large administration of fluids and the administration of glucocorticoids and mineralocorticoids. Fortunately, when addressed in a timely and aggressive manner, an Addisonian crisis is very treatable with supportive care. Left untreated though, Addison disease may turn out fatal.
References
- Healthy Pets Mercola: How to Avoid Addison’s Disease
- Vet Med: Addison’s Disease
- Whole Dog Journal: Canine Adrenal Glands
- Whole Dog Journal: Properly Diagnosing Addison’s Disease and Your Dog’s Treatment Options
