Pathogenetic and clinical aspects of autoimmune thyroiditis

Chronic autoimmune or lymphocytic thyroiditis presents with two clinical entities: a goitrous form, referred to as Hashimoto's thyroiditis, and an atrophic form (atrophic thyroiditis or primary myxedema). Hashimoto's thyroiditis, the prototype of autoimmune thyroiditis, is characterized histologically by diffuse lymphocytic infiltration, and clinically by a typical goiter with or without hypothyroidism. Clinical variants include juvenile thyroiditis (lymphocytic thyroiditis of childhood and adolescence) and focal or minimal thyroiditis. In the latter one the degree of lymphocytic infiltration is milder, and there is either no evidence of thyroid dysfunction or subclinical hypothyroidism. A further variant is the form associated with eye changes of Graves' disease. These conditions may represent different stages of a common disorder, or more probably distinct entities with common pathogenetic mechanisms. There is no good evidence that goitrous thyroiditis precedes atrophic thyroiditis, although in hypothyroid patients the degree of fibrosis increases with age. Most cases of silent (painless) thyroiditis and post-partum thyroiditis recognize an autoimmune origin, but their clinical course is typically transient.