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Hypothyroidism in the American Water Spaniel
By Paul Morrison
Why an article on hypothyroidism?
I suppose I could answer that with a smug, "Why not such an article" but the better answer is "Because it is a problem in the AWS that we have a way of controlling, if only breeders and others would take the time to try." I can also answer that I wanted to write an article because one of my dogs has recently been diagnosed as a probable genetic carrier and is affected by one of the conditions that can lead to hypothyroidism.
Thank goodness the dog is one that we purchased from an outside kennel and not one that is descended from our "line" of dogs. Still, having to pull a dog from a breeding program after years of developing both a relationship with the dog and future breeding plans built around that dog's introduction to the current program is, to say the least, extremely discomforting. Even more discomforting is the fact that there is a potential that this dog has descended from other carriers who have gone undetected either because no test existed prior to a few years ago or because breeders failed to test for this particular disorder once a test was developed.
So, in an effort to be more proactive than reactive, I wanted to take the time to inform other AWS enthusiasts about the thyroid screening test available to us through the Orthopedic Foundation for Animals. I also wanted to use this article to encourage breeders to begin screening their stock for the existence of this condition as a means of weeding out carrier and affected dogs from the gene pool. We do this to weed out AWS that are either potential carriers or affected dogs of other likely health problems including those involving the heart, eyes, and hips and we should do this for hypothyroidism also.
What is hypothyroidism?
Hypothyroidism is a condition that indicates an impaired production and secretion of thyroid hormones causing a decreased metabolic rate. In other words, the thyroid gland produces a low level of thyroid hormone and this reduced amount of thyroid hormone decreases the dog's metabolic rate. According to the Merck Veterinary Manual, this reduction in thyroid hormone affects the function of all organ systems. It is not unusual to see hypothyroid dogs that are lethargic, overweight, intolerant of exercise, have dull coats, suffer from hair loss, or exhibit any number of symptoms if left untreated.
The causes of hypothyroidism can vary but the two most common forms of adult onset hypothyroidism are lymphocytic thyroiditis and idiopathic atrophy of the thyroid gland. To put it more into layman's terms, there are two common conditions that more commonly cause an adult dog to develop hypothyroidism. Both conditions result in the destruction of the thyroid gland over time and both are probably related to some deficiency in the immune system. In recent years researchers have been able to develop a test that helps to determine the existence of one of these conditions, autoimmune thyroiditis, in dogs.
AWS and hypothyroidism
Normally an article with this type of title would be able to detail the proverbial "ins and outs" of this medical condition and how it affects the breed. Unfortunately, for one reason or another, there has never been much study or information regarding this condition in the AWS and, therefore, this article will be unable to do that. This does not mean that the condition does not exist though. In fact, most breeders will tell you that they know of a dog here or a dog there that suffers from hypothyroidism and they will sometimes do so in a very nonchalant manner. The perception of the attitude displayed is discomfortingly characteristic of a person who says something like, "Sure, there are AWS with hypothyroidism. So what? There are worse things to be stricken with you know."
Granted there are worse things that can strike members of our breed. However, that should not mean that we take a devil may care attitude toward the condition. Regrettably though that is what we have experienced in some AWS circles. Yet, it is our responsibility as breeders and AWS enthusiasts to do all that we can to minimize the occurrence of health problems within the AWS. Typically, this is done through both the testing of breeding stock and the promotion of health studies to identify carriers, cure affected dogs, and prevent future occurrences of the disease.
Health studies are costly, time consuming, difficult to initiate, and even more difficult to manage. This is especially true in a tiny breed like ours with its small number of enthusiasts and lack of "big money." Such limitations mean that we as a fancy cannot enter into a thyroid study aimed at eliminating the occurrence of hypothyroidism in our breed. Such a restraint does not, however, prevent us from testing for signs of the condition prior to breeding.
As a person who tries to always breed responsibly and who encourages others to do the same I look to all avenues that I believe will assist me in doing just that. Opportunities to find ways of assuring responsible breeding abound and range from relationships with other breeders that permit information feedback, to the use of health clearances which determine the potential for health problems to arise in my breeding stock. These health clearances can and should be used by all breeders to address potential problems before they become strongly prevalent within the breed. Thanks to research conducted at Michigan State University and the clearance program offered by the OFA we now have the ability to address this potential problem and as responsible breeders we need to do just that.
So what is the fancy to do?
It is not up to me to tell the rest of the AWS community how it should go about its business. I can and do, however, encourage breeders to begin to clear their breeding dogs for eye disorders through the Canine Eye Registration Foundation and for cardiac abnormalities, hip dysplasia, and now thyroid through the Orthopedic Foundation for Animals. Additionally, I encourage AWS breeders to require that any dog used in their breeding program, which does not come from their own kennel, be required to have OFA clearances in the these areas as well. Finally, I encourage all puppy buyers to begin to require that breeders supply a thyroid clearance for their breeding stock just as they should do for eye, cardiac, and hip dysplasia. I warn breeders and puppy buyers alike to not rely on so-called thyroid panels or screens. These tests are inconclusive by themselves and lack the ability to determine whether or not a dog is or may become affected by autoimmune thyroiditis. In fact, if one looked only at the thyroid panel figures of our dog they would conclude that nothing was wrong, however, something is wrong -- he has tested positive for autoimmune thyroiditis and is likely to be hypothyroid at some future time. With everyone taking a proactive position like this we have a greater potential of limiting the affects of hypothyroidism on our AWS.
What is to become of our dog?
The first thing that occurred was that he was immediately removed from future breeding plans. At the suggestion of the researchers at Michigan State University he will be retested in about six months to see if the tests reveal another positive result and to examine how quickly his condition is advancing, if at all. The researchers stated that there is a very slim possibility that he will not develop hypothyroidism or, at least, that he will not develop it until late in life. They also stated though that he is, undoubtedly, a carrier of the condition and is likely to have other carriers in his pedigree's background. It is for this latter reason that we have decided to pull him from our breeding program.
Should he indeed become hypothyroid he will begin to take daily medication for the condition. Basically that will amount to a daily administration of synthetic thyroid medication to maintain proper levels of thyroid hormone and to avoid the problems that occur as a result of the ailment. It is this latter point that causes some to say, "So what?" when it comes to finding out that a dog is hypothyroid. The medication is relatively inexpensive and easy to administer so they see this as somewhat of a benign ailment when compared to other more devastating problems such as heart conditions and the like. The fact of the matter remains, however, that this is a problem that can now be detected and avoided with greater certainty over time. All responsible breeders owe it to the breed and the breed's enthusiasts to utilize this test in order to create a healthier breed in years to come.
What about our other dogs?
After learning of this dog's problem we tested all other dogs within our breeding program. All were found to be normal. Their ages ranged from one year to nine years of age. Future testing will correspond to the suggested ages offered up by the OFA and we hope that all dogs will continue to be shown to be problem free. We also hope that other breeders will recognize the importance of this testing regimen and that our dogs will not remain the only AWS listed within the OFA Thyroid database.
The following information is reprinted directly from the website of the Orthopedic Foundation for Animals. It is reprinted with permission of the Orthopedic Foundation for Animals and can be viewed online by browsing the organization's site at www.offa.org.
General Thyroid Information
Autoimmune thyroiditis is the most common cause of primary hypothyroidism in dogs. The disease has variable onset, but tends to clinically manifest itself at 2 to 5 years of age. Dogs may be clinically normal for years, only to become hypothyroid at a later date. The marker for autoimmune thyroiditis, thyroglobulin autoantibody formation, usually occurs prior to the occurrence of clinical signs. Therefore, periodic retesting is recommended.
The majority of dogs that develop autoantibodies have them by 3 to 4 years of age. Development of autoantibodies at any time in the dog's life is an indication that the dog, most likely, has the genetic form of the disease. Using today's technology only a small fraction of false positive tests occur.
As a result of the variable onset of the presence of autoantibodies, periodic testing will be necessary. Dogs that are negative at 1 year of age may become positive at 6 years of age. Dogs should be tested every year or two in order to be certain they have not developed the condition. Since the majority of affected dogs will have autoantibodies by 4 years of age, annual testing for the first 4 years is recommended. After that, testing every other year should suffice. Unfortunately, a negative at any one time will not guarantee that the dog will not develop thyroiditis.
The registry data can be used by breeders in determining which dogs are best for their breeding program. Knowing the status of the dog and the status of the dogs lineage, breeders and genetic counselors can decide which matings are most appropriate for reducing the incidence of autoimmune thyroiditis in the offspring.
OFA Thyroid Procedures
To identify those dogs that are phenotypically normal for breeding programs and to gather data on the genetic disease autoimmune thyroiditis.
Examination and Classification
Each dog is to be examined by an attending veterinarian and have a serum sample sent to an OFA approved laboratory for testing according to the enclosed application and general information instructions. The laboratory fee will be determined by the approved laboratory. All OFA forms and the OFA fee are submitted with the sample to the approved lab. Check with the referral laboratory for special sample handling and tests for registry purposes.
A breed database number of will be issued to all dogs found to be normal at 12 months of age. Ages will be used in the certification process since the classification can change as the dog ages and the autoimmune disease progresses. It is recommended that reexamination occur at ages 2, 3, 4, 6, and 8 years.
Evaluation of dogs under 12 months of age can be performed for private use of the owner since the few dogs are already positive at that age. However, certification will not be possible at that age.
Dogs with Autoimmune Thyroiditis
All data, whether normal or abnormal is to be submitted for purposes of completeness. There is no OFA fee for entering an abnormal evaluation of the thyroid into the data bank. Information on results determined to be positive or equivocal will not be made public without explicit written permission of the owner.
Thyroid abnormalities fall into several categories-two types will be defined by the registry.
• Autoimmune Thyroiditis
• Idiopathically Reduced Thyroid Function
Autoimmune thyroiditis is known to be heritable.
Those dogs with laboratory results that are questionable, therefore not definitive, will be considered as equivocal. It is recommended that the test the repeated in three to six months.
Approved Thyroid Labs
The laboratory certification process will include quality control, quality assurance and reagent certification. Laboratories may apply and, if successful, will be approved to perform analysis for OFA thyroid certification. A site visit by a qualified veterinary endocrinologist chosen by the OFA will be required and continued quality assurance and quality control will be necessary to maintain certification. Fully certified status can be obtained by passing the site visit and passing the results of the first OFA quality assurance assay result test. The approved laboratory must be contacted for the appropriate submission forms, sample handling procedures, and laboratory service fee before collecting the sample.
Animal Health Diagnostic Laboratory
B629 W. Fee Hall-B
Michigan State University
Lansing, MI 48824-1315
Texas Veterinary Medical Diagnostic
1 Sippel Rd.
College Station, TX 77843
New York State College of Veterinary
607- 253-3673 Animal Health
University of Guelph
Bldg. 49, McIntosh Lane
Guelph, Ontario, N1G 2W1
519-824-4120 ext. 4518
Veterinary Diagnostic Laboratory
Attn: Sample Handling
College of Veterinary Medicine
University of Minnesota
1333 Gortner Ave.
St. Paul, MN 55108
University of California
Veterinary Medical Teaching Hospital
Clinical Pathology, Chemistry, Rm 1017
1 Garrod Drive
Davis, CA 95616
1345 Denison St.
Markham, Ont, L3R 5V2
Veterinarian Instructions for OFA Testing
The veterinarian or owner must obtain the “Application for Thyroid Database”.
The veterinarian and owner must complete their respective portions of the form.
A check for $15.00 payable to the OFA and the completed OFA form must accompany the specimen.
The veterinarian should request the "OFA Thyroid Panel".
Two milliliters (2mL) of serum are needed for testing. The serum sample must be from freshly collected blood. Use a plain "red- top" tube for blood collection. Do not use a serum separator tube with clot additives or any other type of plasma collection tube. After collection, place the blood sample in the refrigerator for 60 to 90 minutes to allow clotting. Centrifuge, collect the serum, and transfer to a plain plastic or glass tube suitable for shipping. Clearly label the sample with the owner's name, animal's identification, date of blood collections, and "OFA Thyroid Panel." If the specimen is to be stored for more than 12 hours prior to shipping, frozen storage is recommended.
Ship to the chosen lab address via an overnight courier service. It is recommended that all specimens be packaged properly and shipped so they are received either chilled or frozen. Serum samples arriving unchilled or at room temperature within 48 hours of the collection date will be accepted. However, samples arriving after this time must be received either chilled or frozen in order to be accepted for registry testing. Contact the laboratory if you have any questions or further instructions are needed. Please do not submit whole blood, clotted blood, or plasma.
Severely lipemic or hemolyzed specimens are also unacceptable. Test results will be mailed or faxed only to the submitting veterinarian and the OFA. Results will not be available from the laboratory by telephone. The OFA will send a report to the veterinarian and the owner.
OFA Thyroid Classification
The method for classifying the thyroid status will be accomplished using state-of-the-art assay methodology.
Indices of thyroiditis
A. Free T4 by dialysis (FT4D)-this procedure is considered to be the "gold standard" for assessment of thyroid's production and cellular availability of thyroxine. FT4D concentration is expected to be decreased in dogs with thyroid dysfunction due to autoimmune thyroiditis.
B. Canine thyroid simulating hormone (cTSH)-this procedure helps determine the site of the lesion in cases of hypothyroidism. In autoimmune thyroiditis the lesion is at the level of the thyroid gland and the pituitary gland functions normally. The cTSH concentration is expected to be abnormally elevated in dogs with thyroid atrophy from autoimmune thyroiditis.
C. Thyroglobulin Autoantibodies (TgAA)-this procedure is an indication for the presence of the autoimmune process in the dog's thyroid.
• FT4D within normal range
• cTSH within normal range
• TgAAis negative
Positive autoimmune thyroiditis
• FT4D less than normal range
• cTSH greater than normal range
• TgAAis positive
Positive compensative autoimmune thyroiditis
• FT4D is within normal range
• cTSH is greater than or equal to normal range
• TgAAis positive
Idiopathically reduced thyroid function
• FT4D is less than normal range
• cTSH greater than normal range
• TgAAis negative
All other results are considered equivocal.