In addition to Primary Addison's Disease or hypoadrenocorticism, (the failure of the adrenal glands to produce the glucocorticoid and mineralcorticoid hormones), and Secondary Addison's Disease (which is the failure of the pituitary gland to secrete ACTH, a hormone which stimulates the adrenal glands), there is a third type of Addison's. That is Atypical Addison's Disease. Atypical Addison's Disease is like Primary Addison's in that the adrenals are at fault, here, too. But, in cases of Atypical AD, the adrenals fail to provide the glucocorticoid hormones, only. In cases of Atypical Addison's, the electrolytes are usually normal. It takes a good diagnostician to ignore the electrolyte information and administer the ACTH stimulation based upon the classic Addison's symptoms these dogs present.
Our Standard Poodle, Beau, is an Atypical Addisonian. At age six months, Beau began experiencing many of the symptoms of a dog with Addison's Disease, i.e., loss of appetite, occasional bouts of vomitting (sometimes blood was present), bouts of diarrhea (sometimes bloody), periods of weakness and lethargy, failure to gain weight, and abdominal swelling (when touched, he exhibited signs that his abdomen was painful). Beau also had episodes where he would run around our bedroom, growling, and stopping to chew at his paws. He would yelp in pain when touched on his back and sides, and often exhibited signs that his jaws were sore and tender to the touch; this made chewing uncomfortable for him. After three months of trying prednisone to control what our Vet believed could be an allergic reaction, and three months of being off and on various antibiotics and antacids in an attempt to control what was happening, our Veterinarian, and we, became concerned about the possible negative affects all of these medications could have on a growing, nine month old puppy. We decided to contact our closest Veterinary Medicine Teaching Hospital, The University of Wisconsin for help. In one phone call, our Vet and the Internal Medicine Specialist at the U of W determined that Beau's symptoms pointed to a possible diagnosis of Addison's Disease. Since our Vet was not equipped to run the ACTH stimulation test, which is the only definitive test for AD, we headed up to the U of W's clinic in Madison, Wisconsin, to either rule Addison's in or out for Beau.
First, the clinic did blood work. The results of the CBC were within normal limits, with the only striking abnormality being elevated liver enzymes. Beau had an ALT of 315 U/L (normal being 0-79). The Docs felt this could be explained by the large doses of prednisone Beau had been taking in our attempt to control what we had believed to be allergies. Most significant within the report was the fact that unlike Primary Addisonian patients, Beau's electrolyte levels were within normal limits. His sodium to potassium ratio ws 29:1. This was not optimum, but above a 27:1 ratio. Below a ratio of 27:1, the patient is considered to be at risk for an Addison's crash.
The U of W then ran the ACTH stimulation test, and this was the defining moment. Beau's pre test cortisol sample was 2 ng/ml. One hour post test, this number had risen to only 3 ng/ml. Contrary to the "normal" electrolyte results, a diagnosis of Atypical hypoadrenocorticism, Addison's Disease (glucocorticoid deficiency only) was confirmed.
Beau takes a glucocorticoid to manage his AD. The choices are: prednisone, prednisolone, hydrocortisone and methylprednisolone (or Medrol). One note about hydrocortisone. Since patients with Atypical AD do not require the mineralcorticoid replacement medications like Florinef or DOCP, the Internal Medicine Docs at U of W felt that hydrocortisone, was not the best choice for Atypical AD patients. Hydrocortisone has the highest mineralcorticoid properties of the glucocorticoids.
One final note, Atypical Addisonians can become Primary Addisonians. This bears watching via regularly scheduled blood testing to evaluate their electrolytes. This does not always occur, but if it ever should, Beau will require the mineralcorticoid replacement properties of Florinef or DOCP. Assuming Beau is feeling and acting well, we do blood work every 3-4 months.
(courtesy Cathy R)
Canine Addison's Disease FAQ