W. Jean Dodds, DVM
Our ongoing database of canine autoimmune thyroiditis (~2000 cases), parallels that being collected at MSU=s Animal Health Diagnostic Laboratory. Certain dog breeds have a relatively high prevalence of this heritable problem. These include: Golden retriever, Shetland sheepdog, American cocker spaniel, Boxer, English setter, Doberman pinscher, Labrador retriever, German shepherd dog, Akita, Irish setter, Old English sheepdog, and Collie, but basically all breeds, and mixed breeds are affected to some extent.
Laboratory and pedigree analyses of affected families show progressive earlier age of onset of thyroiditis and/or clinical signs of thyroid dysfunction, along with increased proportion of affected versus normal offspring in successive litters. This situation has been seen previously with respect to autoimmune hemolytic anemia and thrombocytopenia, and may also apply to Addison=s disease in affected breeds.
Our study also involves ~1000 canine cases presented to veterinary clinics for aberrant behavior. The first 499 cases analyzed with neural network and other correlative programs by Dr. Robert Keller, Chairman, Computer Sciences Department, Harvey Mudd College showed that a statistically significant relationship existed in dogs between:
Thyroid dysfunction and seizure disorder
Thyroid dysfunction and dog-to-human aggression (dog-to-dog aggression showed a trend but was not significant)
Genetic counseling for dog breeders has increased awareness of the need to screen breeding stock on a regular (annual) basis, starting at puberty. Consequently, more animals are diagnosed in the early stages of this autoimmune process, before they begin to show typical signs of thyroid dysfunction. Regardless, these dogs should be removed from the breeding program.
There remains a question about whether to begin supplementation with thyroid hormone immediately, to reverse the production of thyroid autoantibody and the destruction of thyroid tissue, or wait until clinical signs develop. The current report from MSU's one year follow-up of 173 thyroglobulin autoantibody positive dogs, indicated that 20% had converted to clinical hypothyroidism in that time period. Presumably, most of the remaining dogs will eventually become hypothyroid, a finding consistent with our own large study cohort.
Given this expectation plus the fact that dogs with one autoimmune condition are at risk for developing other autoimmune problems (polyglandular autoimmunity and related immune-mediated diseases), we believe that these dogs should begin thyroid replacement once the diagnosis has been established.
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