What is Addison’s Disease

 It is the common name for hypoadrenocorticism, or adrenal insufficiency (an insufficient production of adrenal hormones by the adrenal gland). Since these hormones are essential for life, this is an extremely serious disease and it must be treated as such. It is a disease with symptoms that are common to many other ailments, making diagnosis difficult and sometimes a process of elimination. But once Addison’s is correctly diagnosed, a properly treated dog can live a normal, active life.

The adrenal gland, one on each kidney, is made up of two layers, the cortex and the medulla.  The outer area, or cortex, secretes corticosteroid hormones such as cortisol and aldosterone.  The medulla, part of the sympathetic nervous system, secretes epinephrine (adrenaline), which is generally not affected by Addison’s.

There are three forms of Addison’s disease:  primary, secondary and atypical. 
Primary and atypical Addison’s are usually the result of immune mediated damage to the glands.
Secondary hypoadrenocorticism is from failure of the pituitary to stimulate the adrenals with adrenocorticotropic hormone (ACTH). 
It is important for you to know which type of Addison’s disease your dog is being treated for.

You have to pay close attention to a dog with this problem. Don't ignore any changes in appetite, Gastro Intestinal disturbances or anything else that makes you think your dog is ill. If you work with your vet and are careful about following his or her directions this disease has a good prognosis when it is discovered before a crisis occurs.
 

The symptoms of Addison’s disease can be vague.  More importantly, they are similar to the symptoms of many different problems.  Initially, the dog may be listless, or seem depressed.  Many dogs are described as just seeming off, or losing their normal sparkle.  Lack of appetite is a good indicator. Other symptoms include gastro-intestinal problems like vomiting and diarrhea. Pain in the hindquarters, or generalized muscle weakness such as a dog that can’t jump onto the bed or couch as he has done in the past is not uncommon. There may also be hivering or muscle tremors.  Remember, you know your dog better than anyone. If something doesn't seem quite right, don't wait!...have it checked out.

These symptoms may come and go over months or years making diagnosis difficult.  If the adrenals continue deteriorating, ultimately the dog will have an acute episode called an Addisonian crisis.  Potassium levels elevate and disrupt normal function of the heart.  Arrhythmias can result and blood pressure drops to dangerously low levels.  BUN and creatinine levels, generally indicators of kidney function, are often elevated.  At this point many animals are diagnosed with renal failure, as the kidneys are unable to function properly.  Typically animals are given IV solutions for rehydration, which may produce an almost miraculous recovery.  This too, is a great indication that failure of the adrenals rather than of the kidneys is creating the symptoms.

How can you be sure it’s Addison’s?

One of the first indicators when Addison’s disease is suspected are the electrolyte levels.  The two that are of greatest concern are sodium (Na) and potassium (K).  In addition to looking at these values, it is important to look at the ratio between the two.  This number is derived by dividing K into Na and should be between 27 and 40.  For example, a dog with a Na level of 145 and a K level of 4.5 would have a ratio of 32.  A dog in an Addisonian crisis will typically have a low Na level, elevated K and low ratio.
 

While electrolyte levels are important indicators, they are not the definitive test to determine Addison’s disease.  In fact, with secondary and atypical hypoadrenocorticism, electrolyte levels may not be affected. More severe signs occur when a dog with hypoadrenocorticism is stressed or when potassium levels get high enough to interfere with heart function. Dogs with this problem will sometimes suffer severe shock symptoms when stressed, which can lead to a rapid death. When potassium levels get high, heart arrythmias occur or even heart stoppage which also is fatal. In some cases, especially secondary Addison's disease, there are no detectable electrolyte changes. For a definitive diagnosis the dog is given the ACTH stimulation or response test.  This tests the ability of the adrenal glands to produce the corticosteroid hormone cortisol.

In cases in which the electrolyte levels are normal this is the only test for the problem and it will be missed unless it is looked for specifically. At times this disease can be hard to differentiate from renal failure because the symptoms and even the bloodwork can be similar ---- so the ACTH response test may be necessary to differentiate them.
To perform the ACTH stimulation test, an initial blood sample is drawn and the cortisol level is measured.  The dog is injected with a form of the pituitary hormone ACTH that tells the adrenals to produce cortisol.  After an hour, blood is drawn again, and the cortisol level measured.  Resting cortisol should range from 1-4 μg/dl in the average dog, and should be significantly higher, in the range of 6-20 μg/dl, post-stimulation. (These numbers may vary depending on the lab.) If resting cortisol is low and the dog has no or a low response to the stimulation, the diagnosis is Addison’s disease.  Be aware that some glucocorticoids, such as prednisone, can affect the results of the ACTH test, while dexamethasone does not.

How is it treated!!

There are a number of medications used to treat Addison’s.  The first type acts as a mineralocorticoid and replaces the aldosterone – the hormone responsible for maintaining electrolyte levels.  It is replaced with either an oral medication called Florinef (fludrocortisone acetate) or the injectable Percorten-V (desoxycorticosterone pivalate or DOCP). For dogs that have atypical or secondary Addison’s neither of these medications are used because the production of aldosterone isn’t effected and electrolytes remain in balance.

In addition to replacing the aldosterone, the cortisol, or glucocorticoids, normally secreted by the adrenals must also be replaced.  This is typically done with an oral form of prednisone or hydrocortisone.  With atypical and secondary Addison’s the glucocorticoid is the only medication given. 

What is the final outcome likely to be!!

Addison’s disease will mean that your pet will need medications and monitoring for the rest of his/her life, most dogs with Addison’s can return to their favourite activities. You will learn to understand what his/her stress triggers are and follow your instincts in his/her care.  Together, you will overcome all adversity and you will be able to help your dog lead a normal, full and active life.