Riedel's thyroiditis associated with high titers of antimicrosomal and antithyroglobulin antibodies and hypothyroidism.

Riedel's thyroiditis is a rare, chronic inflammatory disease of the thyroid gland. The aggressive fibrosis with extension beyond the thyroid into adjacent tissues contrasts with the diffuse, but intracapsular fibrosis of Hashimoto's thyroiditis. Most current studies refute the possibility of progression from a highly fibrosing form of Hashimoto's thyroiditis to a Riedel's thyroiditis based on the distinct clinical and laboratory data, although an unknown immunological basis is suggested for both diseases. The authors describe a patient with Riedel's thyroiditis, probably associated with Hashimoto's thyroiditis, sent to surgery because her cytological examination suggested thyroid malignancy. This patient had clinical and laboratory features of hypothyroidism and very high titers of antimicrosomal and antithyroglobulin antibodies, which decreased after surgery. Pathology studies disclosed Riedel's thyroiditis with intense lymphocytic infiltration suggestive of Hashimoto's thyroiditis. Quantitative immunohistochemical studies were not able to distinguish between both diseases.