Visiting Veterinarian : Atypical Addison's
By Michelle Gerhard Jasny V.M.D.
Published: November 5, 2009
Mr. Magoo, the white standard poodle, was adopted by his current owners at two years of age. He quickly racked up a long history of minor concerns. Ear infections, anal gland problems, interdigital pyoderma (infection between his toes), upset tummy, red eyes, itchy muzzle. We treated each malady symptomatically, but when his skin problems became chronic, we tested for allergies. Turns out Magoo has both inhalant allergies (like oak pollen) and food allergies (like soybeans and eggs.)
Desensitization injections and a hypoallergenic diet seemed to improve things for about a year, but this spring Magoo developed recurrent vomiting and diarrhea. "Maybe he got into the cat food," his owner speculated. "Or ate something outside." I agreed that food allergies might be responsible and advised a special diet and variety of medications.
Every time, Magoo would improve, but eventually relapse. We ruled out protozoal infections like Giardia. Though repeated fecal tests yielded no evidence of intestinal worms, we de-wormed him anyway, just to be sure. Magoo's issues persisted into summer. "Let's run basic blood work," I suggested, thinking vaguely about ruling out an adrenal gland malfunction called Addison's disease that poodles are prone to, which can sometimes present these symptoms. But his basic tests were all normal.
"I suspect some form of inflammatory bowel disease," I informed his owner. "Definitive diagnosis requires an intestinal biopsy." Now, I am so old that when I first began practice we would do surgery on dogs like this. Open them up with a nice big incision down the middle of the belly. Look around. Cut out pieces of various parts of the intestines and other organs for the pathologist. Owners who wanted to go really high tech were referred to Angell Memorial. They had a fancy piece of equipment called a fiberoptic endoscope, which could be used to get an intestinal biopsy without cutting patients open.
Nowadays, endoscopic biopsy is routine, although usually still done at a referral center rather than at the office of a country vet like me. Magoo's owner was game to go for endoscopy, as the poor pooch was losing weight and generally feeling miserable, so we packed them off to the mainland.
The doctors at Cape Cod Veterinary Specialists did their physical examination and sent out a battery of tests including a repeat of what we had done here in August, plus a urinalysis, tests for pancreatic insufficiency and malabsorption syndromes, and a cortisol level. They started preparing Magoo for the endoscopy with an overnight regimen of enemas and fasting. The plan was to go from both ends - gastroduodenoscopy to examine stomach and upper intestines, colonscopy to check out the lower. In the morning, before beginning the procedure, the specialist reviewed the test results.
Magoo had slight abnormalities in his white blood cell count. More significantly, his cortisol levels were low. The doctor canceled the endoscopy and ran an ACTH stimulation test. Magoo doesn't have inflammatory bowel disease. He has atypical Addison's disease.
Whuzzat? Well, first you need to understand typical Addison's disease. A dog's adrenal gland has three layers.
In classic Addison's, also known as hypoadrenocorticism, the immune system spontaneously attacks the layer that produces hormones known as mineralocorticoids, which regulate sodium and potassium levels. When these electrolytes get out of balance, all kinds of physiologic chaos ensue. In addition, the adrenal layer that produces corticosteroids, commonly known as cortisone, is often affected as well. Early signs of typical hypoadrenocorticism are vague, including listlessness, vomiting, and diarrhea. About 30 percent of cases are not diagnosed until the dog collapses in an "Addisonian crisis." Typical hypoadrenocorticism is treated by giving mineralocorticoids, either orally or by injection and also supplementing with cortisone if necessary.
But Magoo doesn't have typical hypoadrenocorticism. His is atypical. That little "a" makes a big difference. In atypical Addison's, the mineralocorticoid production is unaffected. Sodium and potassium levels remain normal. That's why our blood tests here in August didn't clue me in to the diagnosis. The problem lies only with the cortisone-producing layer of the adrenals. Cortisone plays an essential part in the body's ability to handle stress, maintaining homeostasis during the flight-or-fight response. But Magoo isn't making enough cortisone. Symptoms of atypical Addison's are just as vague as the typical form and diagnosis depends on running that very specific ACTH stimulation test.
Magoo was started on oral prednisone, a synthetic form of cortisone. He is doing well but will need supplementation for the rest of his life. Standard Poodles have a high incidence of Addison's disease, as do Great Danes, Portuguese water dogs, Rottweilers, West Highland white terriers, bearded collies, and soft-coated Wheatons. Atypical Addison's is much less common than the classic form. In some cases, atypical may progress to typical, so we will be monitoring Magoo's electrolytes monthly for a while, and then several times a year for the rest of his life.
While writing up notes on Magoo's chart and gathering information for this article, I heard the whoosh-whoosh of the office fax machine printing. I wandered over to see what it was. It was from Cape Cod Veterinary Specialists. One of the fun things the docs there do for all us local lugs in general practice is to send us educational faxes, reviewing unusual diseases, diagnostics, and treatments. This fax was entitled "Internal Medicine Mystery Case." There was a drawing of a poodle at the top. I began reading. "A four-year-old male neutered standard Poodle was referred for evaluation of chronic, intermittent signs of vomiting and diarrhea. The referring veterinarian..." Hey! That poodle must be Magoo (although I think he might take umbrage at the frou-frou illustration chosen to represent his distinguished breed). And the referring veterinarian? That's me! We're famous! Okay, maybe not famous, but our story just got faxed to a lot of veterinary offices in Eastern Massachusetts. I guess even the specialists thought Mr. Magoo was an interesting case.
