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March 17, 2016
What is Addison's disease anyway?
What it is, What is looks like, and staying on top of it
The adrenal, one on each kidney, is made up of two layers, the cortex and the medulla. The outer area, or cortex, secretes corticosteriod 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
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 the normal sparkle in their eye. Lack of appetite is a good indicator.
Other symptoms include gastrointestinal problems like vomiting and diarrhea. Pain in the hind quarters, or generalized muscle weakeness such as a dog that can't jump onto a bed or couch as he has done in the past is not uncommon. Shivering or muscle tremors may also be present. The most important thing to remember is that you know your dog better than anyone. If something seems amiss, have it checked out.
These symptoms may wax and wane over months or years making diagnosis difficult. If the adrenals continue to deteriorating, ultimately the dog will have an acute episode called an Addisonian crisis. Potassium levels elevate and disrupt normal functions of the heart. Arrhythmia 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 things to look at when Addison's disease is suspected are the electrolyte levels. The two that are of greatest concern are the sodium (Na) and potassium (K). In addition to looking at these values, it is important to look at the ratio between the two.
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. For definitive diagnosis the dog is given a the ACTH stimulation or response test. This tests the ability of the adrenal glands to produce the corticosteroid hormone cortisol.
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 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 ug/dl in the average dog, and should be significantly higher, in the range of 6-20 ug/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 predinsone, can affect the results of the ACTH test, while dexamtheasone does not.
Keeping on top of it.
There are several 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). Primary Addison' requires the replacement medications of mineral corticoids.
Atypical and Secondary require the replacement of glucocorticoids only.
Atypical Addison's can become Primary and requires careful monitoring of
your dog. Addison's dogs may require additional glucocorticoids during periods of stress, injury or surgery.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.