Combined Riedel's Disease and Fibrosing Hashimoto's Thyroiditis: A Report of Three Cases with Two Showing Coexisting Papillary Carcinoma.

Extensive sclerosis of the thyroid gland can be seen in both benign and malignant conditions. The benign sclerosing lesions of the thyroid include Riedel's disease and fibrosing Hashimoto's thyroiditis. Although these conditions usually occur separately, rarely can they occur simultaneously. In malignant lesions, papillary thyroid carcinoma and anaplastic carcinoma of the thyroid can be associated with extensive sclerosis leading to partial or total effacement of the tumor. We report on three cases that showed simultaneous occurrence of Riedel's disease and fibrosing Hashimoto's thyroiditis. Two of these cases also showed papillary carcinoma (one case of Warthin's-like papillary carcinoma and one case of classic type). All patients were females (age range 32-67 yr) and presented with elevated antithyroglobulin antibodies. Two patients presented with a solitary thyroid mass, and from these one had multiple bilateral neck nodes and a paravertebral mass. The third patient presented with a multinodular gland adherent to neck structures. All patients underwent total thyroidectomy. Histologic sections showed extensive replacement of the thyroid parenchyma with dense keloidal fibrosis, intermixed well-developed lymphoid follicles, and scattered lymphocytes and plasma cells. In all cases the fibrotic process extended beyond thyroid capsule with involvement of the perithyroidal soft tissues and skeletal muscle consistent with Riedel's disease. One case showed a classic papillary carcinoma with bilateral lymph node metastases, and the other showed a Warthin's-like papillary carcinoma. In both cases the papillary cancers were surrounded by dense sclerosis. Immunohistochemical stains for B- and T-markers and immunoglobulin light chains showed a polyclonal population of the lymphoid cells. The simultaneous occurrence of Riedel's disease and fibrosing Hashimoto's thyroiditis is rare and most likely represents a coincidental phenomenon, because both of these conditions are distinct clinicopathologic entities.