Abstract: Objective To evaluate the clinical and pathological features of Riedel's thyroiditis (RT), and current diagnostic and treatment methods for that disease. Methods Five RT cases identified by surgery and pathological examinations at Peking Union Medical College Hospital from 1985 to 2009 were analyzed and compared with the cases reported in the literature in terms of clinical and pathological features. Immunohistochemical staining of kappa and lambda light chains was carried out for RT tissues from all the five patients. Results All the five cases were females, aged 45-55 years. Elevation of serum thyroid autoantibodies was found in only one patient, who had longer disease duration than the others. Pathological examination revealed invasive fibrosclerosis of the thyroid follicles, thyroid capsule, and the surrounding tissues. In RT tissues, the number of cells containing lambda chains was a little higher than those containing kappa chains. Conclusions RT is a rare disease which might be more common in middle-aged females than in other populations. Pathological features include the destruction of thyroid follicle, extension into surrounding tissues by inflammatory cells and fibrous tissues. Immunohistochemical staining of kappa and lambda chains could help diagnose RT.

Key words: Riedel's thyroiditis, chronic fibrous thyroiditis, Hashimoto's thyroiditis, differential diagnosis, pathological features