Autoimmune Thyroiditis

The thyroid gland sits on the throat below the larynx. Its function is to produce thyroxine. a hormone that controls metabolism. Autoimmune thyroiditis is an immune-mediated disease characterized by inflammation of the thyroid gland which is inflitrated by lymphocytes that destroys the thyroid gland. The disease very often leads to hypothyroidism.

Breeds at Risk

Autoimmune thyroiditis is particularly often seen in Doberman Pinscher, Beagle, Golden Retriever, Borzoi, Great Dane, Newfoundland, Rottweiler, Chow Chow, Boxer, German Shepherd Dog, Old English Sheepdog (Bobtail), Maltese, Cocker Spaniel, Airedale Terrier, Skye Terrier , Poodles, Shetland Sheepdog and Akita.

Autoimmune thyroiditis, also called lymphocytic thyroiditis, has also been reported with increased prevalence in Irish Setters and Dachshunds which are a genetically susceptible breeds. Research suggests that the onset of this disease occurs in pubescent Irish setters before the onset of hypothyroidism.

Autoimmune thyroiditis has now been identified in more than 50 breeds. The condition is heritable in those breeds that have been studied, and progression to hypothyroidism, if it occurs, can be slow. This condition may occur as part of other systemic diseases such as lupus, rheumatoid arthritis or idiopathic arthritis.

Types of Hypothyroid Diseases

There are four hypothyroid syndromes. The two primary forms are lymphocytic thyroiditis and atrophic hypothyroidism, and the two secondary forms are pituitary-dependent hypothyroidism and euthyroid sick syndrome.

Lymphocytic thyroiditis resembles Hashimoto's thyroiditis in man. Lymphocytic thyroiditis is a common canine condition which is associated with more than 50% of cases of canine hypothyroidism.

Dogs are affected between ages 1 and three years. Less than half of the affected dogs manifest obesity. Most individuals experience lack of energy and recurrent infections. A large number of dog skin disorders are caused by thyroid disease.

CAUSES
Lymphocytic thyroiditis may be initiated by medications, vaccinations, viral infections, and heavy metal toxicity from water and food supplies.

Dogs can live for years with thyroiditis without there being any signs. The presence of anti-thyroid antibodies in the dog's blood or tissues marks the disease, during which the dog becomes susceptible to immune-mediated or other diseases. The primary indicator on the thyroid profile is elevation of the T and/or T4 antibodies. Factors that influence the progression from subclinical thyroiditis to hypothyroidism in dogs are still to be identified.

The Importance of Early Testing

An autosomal recessive mode of inheritance has been suggested. Breeders should test thyroid levels in their dogs upon the onset of puberty, and then annually thereafter.

Because thyroid hormones play a role in the metabolic function of all cells, the symptoms affect all systems, blood, neuromuscular, skin, circulatory, gastrointestinal, reproductive system and so forth. Early in the disease, the disorder can be identified through blood tests; the symptoms do not appear until the thyroid gland loses its reserves and can no longer compensate for the throid antibodies. This disorder can be treated with thyroid hormones.

References:
1. Irish Setter. Margaret Williams
2. Lymphocytic thyroiditis. Graham PA, Nachreiner RF, Refsal KR, Provencher-Bolliger AL. Vet Clin North Am Small Anim Pract. 2001 Sep;31(5):915-33
3. Holistic Guide for a Healthy Dog. Wendy Volhard, Kerry Brown
4. Genetics: An Introduction for Dog Breeders. Jackie Isabell