Higher magnification of the inflammatory infiltrate showing numerous plasma cells, lymphocytes, and eosinophils. Riedel thyroiditis can coexist with a variety of IgG-4 related systemic inflammatory fibroscleroses including mediastinal or retroperitoneal fibrosis, sclerosing cholangitis, and inflammatory pseudotumor of the orbit. The treatment usually consists of steroid therapy. Thyroid hormone replacement is not required as most patients are euthyroid. Compression symptoms may require surgical intervention.