What is lymphocytic thyroiditis (autoimmune thyroiditis)?
Lymphocytic thyroiditis is the underlying cause in many cases of primary hypothyroidism in dogs and the predisposition to its development is believed to be highly heritable. It is an immune mediated disorder characterized histologically by a diffuse infiltration of lymphocytes, plasma cells, and macrophages in the thyroid gland. Antibodies interact with the follicular cell, colloid, or thyroglobulin antigens and activate the complement cascade and cell-mediated cytotoxicity. The progressive destruction of follicles and secondary fibrosis eventually leads to a failure of thyroid hormone production. More than 60 or 70% of the thyroid tissue needs to be destroyed before we see changes in laboratory measures of thyroid function. This process can take months or years to cause classic hypothyroidism. In some animals it may not progress. Anti-thyroglobulin antibodies are released into the circulation in animals with this condition. A test for these antibodies in serum is included in the Michi
