Chronic autoimmune thyroiditis and rheumatic manifestations.

A variety of rheumatic manifestations have been described in association with autoimmune thyroiditis. In the past, most of these manifestations were attributed to the underlying thyroid dysfunction, in particular hypothyroidism. However, a responsibility of the mechanisms involved in the autoimmunity rather than a direct action of thyroid hormones seems supported by the evidences that some rheumatic manifestations may occur even in euthyroid patients, or that they are more frequent in hypothyroid patient with autoimmune thyroiditis than in those without this disease. Rheumatic manifestations could be sometimes attributable to the autoimmune rheumatic diseases frequently associated with autoimmune thyroiditis, such as Sjögren's syndrome, rheumatoid arthritis, systemic lupus erythematosus, or scleroderma. Among the most important or frequent rheumatic manifestations there are a mild non-erosive variety of arthritis, polyarthralgia, myalgia, and sicca syndrome without a true Sjögren's syndrome. Although the possible pathogenesis of these manifestations is not completely established, some hypotheses may be proposed, including a role of autoantibodies characteristics of autoimmune thyroiditis, a possible overlap between autoimmune thyroiditis and some autoimmune rheumatic diseases, and a systemic inflammatory reaction associated with thyroiditis.