VetInfo Digest July 1998
This issue
What Do Those Tests Mean? Part II
Demodecosis in Older Dogs
A Little Bit About Us, Our Website and the VetInfo Digest
New Stuff
The Pony Swim
A Shorter Version
What Do Those Tests Mean? Part II
Last month we talked about commonly run laboratory tests in veterinary medicine and what they meant. Since it seemed like a good idea to start with "clear cut" tests, I stuck to the ones that have positive and negative results. Those are confusing sometimes. But what about less clear cut tests, like thyroid testing?
There are two distinctly different groups of diseases associated with the thyroid gland in dogs and in cats. Dogs tend to get hypothyroidism, or levels of circulating thyroid hormone that are too low. In general this is associated with lethargy, heat seeking, weight gain, poor immune response to disease, hair loss, infertility and chronic skin infections. Not all dogs exhibit all signs. Cats tend to get hyperthyroidism, which is circulating levels of thyroid hormone that are too high. The hallmark sign of this disease is increased appetite with weight loss. A smaller set of cats develop a loss of appetite but still have weight loss. Affected cats may be restless, they may vocalize more than in the past, they have high heart rates and eventually they will develop serious organ damage associated with the hyperthyroidism such as heart failure or kidney failure. There are big gray areas in testing for hypothyroidism and for testing for hypothyroidism.
If your vet suspects that your dog has hypothyroidism there are a number of possible ways to test for the condition. Some vets just give thyroid medicine and try to judge the need for it based on the results of administering the pills. I am uncomfortable with this approach because thyroid supplementation is usually a lifelong necessity and I hate to base the need for a long-term medication on a clinical response, since that can be very misleading. The least expensive test to run is a total T4 level (TT4). If a dog has a high normal total T4 level it is unlikely that it has hypothyroidism. This makes it a very good screening test. It is inexpensive and if the levels are high, you are done (see exception below). On the other hand, if the level is in the lower half of the normal range or below normal this test is not very useful. Almost any severe illness, including skin infections, will cause a drop in the total T4. It is not unusual for dogs with a severe systemic illness to have TT4 levels lower than the normals for all dogs despite having normally functioning thyroid glands. Some dogs with hypothyroidism can have total T4 values that fall within the low end of the "normal" range and in a small number of cases in which antibodies against thyroid hormone are present a dog with hypothyroidism can have TT4 levels in the high end of normal or even higher than normal levels. If your vet really really thinks that your dog has hypothyroidism and the TT4 is in the high normal range, it may be a good idea to check for antibodies against thyroid hormone. This test is part of the panel of thyroid tests run by Michigan State University’s lab.
In the past, it was possible to do a test known as a TSH response test. Blood was drawn in the morning and thyroid stimulating hormone (TSH) was administered immediately. TSH should stimulate the thyroid glands to release thyroid hormone. Blood was drawn again later in the day (usually 6 to 8 hours). If the TT4 level was significantly higher than the morning value, the dog was considered to be normal and if there was no or little response to TSH then the dog was considered to be hypothyroid. This is still considered to be the most accurate test and would probably still be widely used except that TSH is no longer readily available to veterinarians, making it impossible to do this test. Many vets were hesitant to use this test when it was available due to the cost of TSH and the fact that the clinical signs of hypothyroidism mimic enough other diseases that a lot of dogs were tested for hypothyroidism that didn’t have it. Even though it was a good idea to check on the thyroid status clients were often a little touchy about a $100 test that came out negative for hypothyroidism.
Currently the best available test for hypothyroidism is to run a "thyroid panel" that includes at least a free T4 level done by a testing method known as equilibrium dialysis and a canine TSH level. Free T4 is the portion of the total T4 that is not bound to anything in the circulation. Unbound T4 is the active portion of the total T4. It can be measured by several methods but the most accurate is the equilibrium dialysis method. Several veterinary labs offer FT4 testing by equilibrium dialysis. It is not part of the standard panel run by Michigan State University but is included in their premium panel. If the FT4 level is low there is a very high correlation with hypothyroidism, approximately 98% based on a report by Peterson et. al. in the Journal of the AVMA. The canine TSH level measures thyroid stimulating hormone. If the thyroid gland can not produce adequate thyroid hormone the dog’s regulatory system is stimulated to ask for more thyroid hormone. The way it does this is to produce thyroid stimulating hormone. Therefore, when a dog has hypothyroidism the level of TSH should theoretically be high. If the canine TSH level is high while the FT4 is low, the diagnosis of hypothyroidism can be made with great confidence. About 25% of dogs will have normal TSH levels despite having hypothyroidism, though. So currently, the FT4 by dialysis is the most accurate test, especially when combined with a cTSH test.
There are two other problems with thyroid testing that are important to understand. The first relates to pets that will be used for breeding and attempts to screen for hypothyroidism. Screening is a little frustrating since dogs that will eventually develop hypothyroidism usually do not have measurable hypothyroidism while they are young. They may develop anti-thyroid hormone antibodies early in life, though. So an effort to screen for hypothyroid tendencies in breeding animals should probably include a test for anti-thyroid hormone antibodies. The second problem is one of timing. Your dog may exhibit signs of hypothyroidism when it is five or six years old. Your vet may test for hypothyroidism and decide that your pet does not have hypothyroidism. The cause of the signs may be identified and treated. Then when your pet is eight or nine years old they might return. The earlier test has no value in ruling out hypothyroidism now. Your dog must be tested again. It is entirely possible for a dog to have negative tests for hypothyroidism at an earlier age and then develop it a later age. My personal record for testing a dog for hypothyroidism that never developed it was four tests. It just has to be ruled out when clinical signs are present, even though tests have been run before. My personal record for testing for hypothyroidism in a dog in which it eventually was the problem is three tests, so repeated testing is not always in vain. This disorder is frustrating to diagnose. Thyroid testing may be the test procedure that is most commonly misinterpreted in veterinary medicine. Work with your vet to get it right.
Unfortunately, hyperthyroidism, the disorder seen most commonly in cats, can be just as frustrating to diagnose. In most cases, this diagnosis is pretty straightforward. Most cats with hyperthyroidism probably do have total T4 levels that are above normal. If a TT4 level is above the normal range for your vet’s testing lab, your cat probably does have hyperthyroidism. TT4 levels are a useful screening test for this disorder. As cats age, their TT4 levels appear to drop in comparison to normal, though. A fifteen year old cat with a TT4 in the upper half of the normal range for all cats may still be hyperthyroid. If clinical signs of this disease are evident, especially weight loss that is not explained by other disease, it may be necessary to do more specialized testing in order to rule out hyperthyroidism.
As in dogs, the free T4 test is thought to be a more accurate assessment of the thyroid level than a total T4 test. The FT4 is often elevated in older cats whose TT4 value is in the middle or low end of the normal value for all cats but who actually have hyperthyroidism. The free T4 can be elevated due to non-thyroidal illness in cats, though. This is particularly true in the case of kidney disease which is also very common in older cats. If the free T4 level is used for the evaluation of hyperthyroidism in a cat it is important to check a complete blood panel for other signs of illness.
If any question remains in the veterinarian’s mind about the possibility of hyperthyroidism after the free T4 value is known, there is another test that is very helpful in distinguishing cats with hyperthyroidism from the normal population of cats. The (Triiodothyronine [T3] suppression test) T3 suppression test is another test that uses the body’s natural regulatory mechanisms to help determine if a a problem exists. The test is run by drawing blood on the first day and freezing this blood sample. Then the cat is given triiodothyronine (T3, Cytomel Rx) every 8 hours for 7 doses. Blood is drawn 2 to 4 hours after the seventh dose on the morning of the third day and sent to the lab for T4 evaluation along with the sample drawn the first day. If there is a significant decrease in the concentration of T4 in the second sample it is very likely that hyperthyroidism is present.
That was probably more than most of you want to know about testing for thyroid disorders but it is estimated that as many as 25% of cats may develop hyperthyroidism in their lifetime and hypothyroidism is the most commonly diagnosed hormonal disorder in dogs. There is a good chance that someday your vet may be considering one of these disorders as a possible problem in your pet.
Demodecosis in Older Dogs
We have received several inquiries this month about older dogs suffering from new outbreaks of Demodectic mange. It is very important to understand why demodecosis is different in an older dog.
Demodex canis mites exist in the skin of most dogs. They are usually infected by their mother as they nurse. The mites live in the hair follicles in small numbers and do not cause problems. In humans, Demodex folliculorum is a fairly common resident of hair follicles. For most dogs and for most humans, Demodex mites are a relatively harmless parasite.
In a few young dogs, the mites do much more than live peacefully in a few hair follicles. They reproduce in an uncontrolled fashion and soon cause hairloss, allow secondary bacterial infections, suppers the immune system and cause serious disease and even death in extreme cases. Demodecosis that occurs in a few spots, usually less than five and confined to the head area, is said to be "localized". Approximately eighty percent of puppies outgrow localized demodecosis without treatment. The remaining puppies appear to be incapable of mounting an adequate immune response and become infected over a larger area and suffer more secondary problems. These puppies are said to have "generalized" demodecosis. It appears that this is an hereditary condition and puppies who are known to have generalized demodecosis shouldn’t be bred.
Most dogs have developed a strong immunity to Demodex mites by the time they are a year or so old. It is unusual to find a new case of demodecosis in an older dog. Usually, when this does happen, there is an underlying cause that is leading to immune suppression and the emergence of the demodecosis. Finding that cause is very important. If a treatable primary problem exists it is more likely that the demodecosis can be successfully managed.
The two most commonly identified natural causes of demodecosis suddenly occurring in older dogs are hyperadrenocorticism (Cushing’s disease) and hypothyroidism. The two most common human induced causes of demodecosis are the use of chemotherapeutic medications in the treatment of cancer and the overuse of corticosteroids in the treatment of other conditions such as allergies.
If a dog is being treated for hypothyroidism or hyperadrenocorticism and demodecosis occurs it is a sign that the therapy for the condition should be reevaluated to be sure it is effective. In some cases it will be but in other cases reestablishing control of the underlying disease will help a great deal with treatment of the Demodex mite infestation. Obviously, if cortisones are being used for a condition that can be controlled in any other way and demodecosis occurs it would be best to decrease the corticosteroid dosage or discontinue corticosteroids if possible.
It is almost always possible to treat for the Demodex and the underlying condition at the same time. Since Demodex mites seem to be able to induce immune suppression or at least change the follicular environment to favor bacterial infection it is important to eliminate them if possible.
In older dogs, it is often necessary to continue using a medication to suppress the mites on a continuous basis. Once a month dips with amitraz (Mitaban Rx) or administration of ivermectin on a regular basis may allow a dog to live with the Demodex successfully.
D. D. Duclos, et al, reported in the February 15th, 1994 issue of the Journal of the American Veterinary Medical Association a retrospective review of 41 cases of adult onset demodecosis. Of these dogs, 29 had an identifiable underlying disease. Of the dogs in which treatment was attempted, the disease could not be cured or managed in only five dogs. In twelve of the dogs in the study it was not possible to find an underlying cause for the demodecosis. This is a little less than one-third of the cases. Most older dogs benefit from a careful search for the problem that is leading to demodecosis.
A Little Bit About Us, Our Website and the VetInfo Digest
We appreciate the support that all of our subscribers have given us. The VetInfo website has grown much faster than we anticipated it could. Our Internet Service Provider charges have grown with the huge amount of data transmission that the site now generates. Some of you have written to us and asked what makes us put in the effort to provide this site or asked how we can provide it without advertising. It seems like it might be a good idea to explain our background and our thoughts on providing a veterinary information website.
I am Dr. Michael Richards, a veterinarian who graduated from the Iowa State University College of Veterinary Medicine in 1979. I spent almost one year working for a mixed animal practice in Virginia after I graduated from veterinary school. I decided that I didn’t have the personality to work for someone else and set up my own practice. My intention was to work with farm animals and horses when I started my practice. I only had $600 in the bank at the time and it was the only type of practice that I could afford. I put my money into leases on equipment and drove from farm to farm in my chosen territory letting people know I was available. Fortunately lack of realistic planning did not impede my success and I was able to survive the first year of practice. Many of my clients wanted me to work on their dogs and cats when I was at the farm. Soon it became apparent that I couldn’t really serve these people’s needs without a clinic. So we built one. It grew too. Our house was next door to the clinic and we were able to watch our children grow, too. Five years after we started our business my wife went to veterinary school as well. She graduated from the Virginia-Maryland Regional College of Veterinary Medicine in 1989. She had no interest in farm animal medicine and I was badly injured in a collision with a cow shortly before she graduated from vet school. Faced with a year or so of rehabilitation I decided to abandon large animal work and be a full time companion animal vet. Sometimes on really nice days I miss the farm calls but most of the time I am content it was the best decision. I discovered that almost all the time I could work with my wife and we have been in practice together for the last nine years.
We have been deeply committed to educational causes and my wife is a School Board member in our community. Our practice is rural and it will never really be a two veterinarian operation, so we had time to attend meetings and to work as volunteers in the community. The experience was always very rewarding. I have always enjoyed helping clients understand their pet’s problems. I have always felt that veterinarians should do a better job of communicating with clients because there are always people who are much less informed but much more willing to give their opinion of pet health care issues. It seemed like providing a good reliable source of information had to be possible. Computers seemed like the answer, somehow. When I discovered the Pet Care Forum on America Online I really enjoyed answering questions about pet health issues online and did this for several years. Ultimately, though, I was still working for someone else and once again found myself restless to do things my way. It took me a while to decide that a website could work as well as bulletin boards and chat rooms for providing information. I think we have proved that it can be, especially with the advent of better search engines. We hope to provide the best available source of information on veterinary medicine and pet health issues.
Michal Justis is our web site designer and graphic artist. I write the text and she does everything else. Michal has always had a strong interest in animals and was a cofounder of WildCare, Inc., a wildlife rehabilitation organization. She was also a receptionist at our practice for about ten years. Her art interests include sculpturing, sketching and graphics. It was hard to convince Michal that art and computers could coexist but once she started viewing websites as artistic endeavors there was no stopping her. She learned search engines, web design, HTML code and a number of WYSIWIG website production programs. Michal worked almost full time on the website for about a year before it was necessary for her to move back to the city. Now she manages it and a full time job. Our collaboration is all done over the web.
I probably average two or three hours a day answering questions or writing the VetInfo Digest. I don’t mind putting in the time at all. Michal spends a great deal of time putting the answers online and creating new pages as the information expands. We would like to someday have the ability to work on the website full-time and for it to support us. We are hoping that our time worn plan of leaping, then looking, will continue to work as well as it has in the past.
Our problem with money originates with our philosophies. We want to be able to put accurate information online with as little bias as possible. We want the information to be scientifically valid whenever possible and we try hard to point out when information on the site can not be substantiated in that manner. And we want to answer the questions that people need to have answered, as honestly as it is possible to answer them.
Almost no pharmaceutical company, pet food manufacturer or potential sponsor likes all of what is on our site. We have tried to find a sponsor to help fund the site without too much luck. The initial cost of a website is not very high and so we just didn’t worry about whether or not we were making money (at least not a lot). As the site has grown in size the cost of hosting it has risen quite a bit. Subscriptions to the VetInfo Digest now pay for about half the cost of running the VetInfo website for one year. We think providing a good quality veterinary information site is important. We hope to continue to be able to provide searchable information for free through the sales of subscriptions to our newsletter. However we have been considering making the website subscription based. Right now, the biggest advantage to us would be a decrease in traffic, reducing the cost of providing the site substantially as throughput decreased. This runs counter to our goal of providing good quality information that anyone can access, though. We’ll be sorting through our goals and our needs over the next few months and will keep you informed of any changes. If we go to a subscription only format for the website all of our present supporters will have access with no additional fee for the full duration of their subscriptions.
It is a challenge to start a new business on a new and rapidly changing medium but we hope to stick it out for a long time. As always, we appreciate your support.
New Stuff
Program (TM), the once monthly oral flea control medication is now available in a new formulation, a once every six months injection. The injection is only approved for cats at this time. We haven’t used the injection yet but lufenuron, the active ingredient, has been very safe in previous formulations.
New diets are available for food trials. If you have a dog with a long history of skin disease that has never been tested for food allergies due to the difficulty in finding a commercial diet with no ingredients your dog has ever eaten, now may be the time to reconsider food sensitivity trials. Purina has a new diet that is formulated from low molecular weight proteins which are believed by nutritionists to be hypoallergenic and another food, Exclude (TM) is also manufactured with these proteins. Hill’s has several new formulations of their d/d hypoallergenic diets and Innovative Diets also produces several different hypoallergenic diets. With the availability of a number of diets it is possible to find one that will work in a food trial for most dogs. While it is too early to tell for sure, it appears that food allergies may be a little more prevalent than previously believed and this really might be a good time to consider a food sensitivity trial for pets with a history of chronic itchiness that doesn’t appear to be strictly seasonal or that is only partially responsive to treatment.
The Pony Swim
There is an area of my practice territory in which the inhabitants haven't changed much in nearly 300 years. Some families have eked out a hard existence from fishing and farming along the shores of the Chesapeake Bay tributaries from generation to generation since arriving here shortly after John Smith and the Jamestown settlers. In some ways, the families that have clung together through the centuries and survived the mosquitoes and the weathered the tides are a hard lot. They don't take well to strangers and they settle their differences themselves with gaffing hooks and Friday night brawls.
Their world is changing rapidly, though. Land once thought to be less than desirable due to the mosquitoes and tidal marshes has become the fashionable place for retirees and folks with the money for summer homes to settle. Land that once was marked with homemade navigational aids and duck blinds now holds expensive homes and sports fencing for horses. The old families have moved inland a little on the profits from their formerly worthless land. A few of the really entrenched families moved onto the small islands in the area, to keep up an isolated lifestyle or to avoid entanglements with the law.
I was working at a new horse farm on a little peninsula that jutted out towards one of the bigger islands. There were five or six houses along the edges of the peninsula, all of them less than five years old. Each one with its own barn and paddock. Each paddock was a muddy or dusty corral, depending on how long it had been from the last rain. The marsh soil just didn't support grass well while being trampled by horses.
I looked back down the long driveway and noticed a little puff of smoke. In the spring in the Guinea area, marsh fires are common. Rumor has it that the local watermen find it easier to look for asparagus after the marsh is burned away and that the fires are started in these searches. The driveway was built up out of the marsh several feet and it was the only way out. It didn't look like this was going to be a big problem but I kept my eye on it during the farm call.
My technician, Susan, got out and asked if we had found the right house. This was a new client. She waved back at me to start unpacking the truck. We were here to castrate an Arabian colt. The owner approached me as I worked.
"Doc, you got time to castrate a pony stallion while you're here"?
It always takes a while for the horses to wake up from castration. So adding the pony to our surgery list really didn't extend the farmcall too much and I agreed to do it. Besides, we weren’t going anywhere until the fire trucks got out of the driveway. Soon both the little Arabian colt and the even littler pony were laid out on the ground recovering from surgery. Our equipment was cleaned up and was back in the truck. Horses sometimes have a difficult time with recovery from anesthesia and I was holding the Arabian's lead while the owner held the pony's lead. After a couple of minutes of general conversation, the conversation drifted to questions about recovery from the surgery.
"How soon can the pony swim, Doc?"
Right away I knew I was in trouble. "Swim?", was all I could think of to say.
"Well, yeah, Doc. The pony swims a lot."
I worked a lot for the "guineamen". I knew that making them mad was not a good idea and that I wasn't going to like the rest of the horse owner's story, but that I better find out what was going on.
"Why does he need to swim?"
Now it was the owner's turn to be a little nervous. "Well, Doc, he really doesn't belong to me or the neighbors, but we all contributed a little to getting him castrated. He swims over from that big island and breeds the mares!"
Just then, the Arabian woke up. Once he was steady on his feet, I walked back to the truck and picked up my emasculator.. Susan trailed behind a little, curious to see what was going on. We stopped, looked back up the driveway and determined that the fire still had us trapped on the marsh but that the fire department appeared to be in control of it now. We would have a few minutes to kill, though.
We walked back over to the pony and I started talking to the owner about the surgery. "You saw how we castrated him, right? We used this emasculator that has a wide crushing jaw on one side and a sharp cutting blade made to swing across after the spermatic cord is thoroughly crushed. We didn't suture the scrotum because there is drainage in horses and it is best to allow it to drain out of the scrotum. For a couple of days it would be best if the scrotal area is flushed with a hose for the cooling effect and to keep it clean. I suppose swimming would probably do the same thing. I guess he can probably swim tonight or tomorrow." The Arabian’s owner looked relieved.
"One more thing, Mr. Pierce. If you ever tell anyone who castrated that pony, I am going to come back and give you a very personal demonstration of how that emasculator works". I did my best to smile menacingly while relaying this message.
One of the firemen drove up just as I got done explaining how serious I was about keeping this whole incident quiet. I knew that the Islanders wouldn’t really care about the pony being castrated but that they wouldn’t like not being asked first. I really did want Mr. Pierce and his neighbors to keep this little secret to themselves. There wasn’t much more to be said and I was relieved when the fireman said we could safely leave.
As far as I know, no ever told how the pony stallion became a pony gelding. At least I never heard a word about it and none of the "guineamen" ever tried to stick a gaffing hook in me.
A Shorter Version
Occasionally, when a dog is castrated, the scrotum will fill up with blood. This gives the appearance that the surgery was not done in some cases and once or twice a year I have a dog owner come in after a castration surgery and ask me, usually sheepishly, but sometimes angrily, "Are you sure you castrated my dog?"
Generally a short explanation is necessary and an exam to be sure there isn’t an infection or some other cause of swelling. Then we explain that sometimes the blood clot will "organize" and form a small lump (or two) in the scrotum, giving the appearance that testicles are present when they are not. Most dog owners are accepting of this but seem to have some reservations about the whole thing as they leave the office.
But not always. On one occasion, the woman I was explaining all of this too stopped me as I apologized for not remembering to tell her that this outcome was possible. She said, "Doc, this is great. Now my neighbor will never know I had this done." And another woman said to me, at about the same time, "Well that saves me a lot of trouble trying to figure out how to tell my husband I had his dog castrated!"
If You’re in the Philadelphia Area....
... and you want to cheer me on in my first ever rowing race, come on down to Fairmont Park on July 4th and look for an old guy with a gray ponytail rowing a single shell. Or wait until July 5th and look for two old guys -- a former Marine fighter pilot (short hair, big muscles) rowing with a 60’s holdover (long hair, less muscles).
As always, we sincerely appreciate your support of the VetInfo Digest and the VetInfo Web Site. It is much easier to provide these services with your help. Thanks! Copyright, TierCom, Inc., 1998 Tiercom, Inc. P.O. Box 476 Cobbs Creek, VA 23035 The opinions expressed in this newsletter are solely those of the author, Michael Richards, DVM, unless otherwise noted in the text. Michal Justis is our web designer and graphic artist.