Hashimoto's thyroiditis and Graves' disease associated with retroperitoneal fibrosis.

Retroperitoneal fibrosis is a rare disease of uncertain pathogenesis. However, its possible association with several immunopathologic conditions, the possibility of systemic involvement by the fibrous process, the presence of various autoantibodies, and the frequent response to immunosuppressive treatment all support an autoimmune pathogenesis. Riedel's thyroiditis is a rare disease the pathogenesis of which is also thought to be immune-mediated based on its optimal response to steroids; Riedel's thyroiditis is also frequently reported in association with retroperitoneal fibrosis. We describe here two cases of autoimmune thyroid disease associated with retroperitoneal fibrosis, the first with features of primary myxedema, the second of primary thyrotoxicosis. Histology of retroperitoneal fibrosis is documented and it is compatible with an immunopathologic condition. Thus, these two cases add further support to the hypothesis of an autoimmune pathogenesis of retroperitoneal fibrosis and indicate the importance of carefully monitoring for the development of other autoimmune disorders, i.e., of the thyroid gland, in patients with retroperitoneal fibrosis.