Basedow's disease with associated features of Hashimoto's thyroiditis based on histopathological findings

Basedow's disease and Hashimoto's thyroiditis are autoimmune thyroid disorders and usually diagnosed with elevation of serum autoimmune antibodies. Thyrotropin receptor antibodies (TRAb) and/or thyroid-stimulating antibody (TSAb) are usually used for diagnosis of Basedow's disease, and thyroid peroxidase antibodies (TPOAb) and/or thyroglobulin antibodies (TgAb) are for diagnosis of Hashimoto's thyroiditis. However, it is difficult to diagnose a subject as Basedow's disease with associated features of Hashimoto's thyroiditis only with elevation of such autoimmune antibodies.

A 44-year-old woman with 5-year history of Basedow's disease underwent a total thyroidectomy. She did not have a goiter. TRAb, TSAb, TPOAg and TgAb were all positive before a total thyroidectomy. In histopathological macroscopic examination, diffuse hyperplasia of the thyroid gland was observed. Furthermore, in histopathological microscopic examination, both characteristics of Basedow's disease and Hashimoto's thyroiditis were observed. After a total thyroidectomy, titers of all thyroid-associated autoimmune antibodies were markedly reduced.

Herein, we report a subject with Basedow's disease without a goiter whose TPOAb and TgAb were relatively high at the onset of Basedow's disease. In addition, interestingly, the histopathological findings of this subject showed direct signs of Basedow's disease and Hashimoto's thyroiditis in the same thyroid gland. Considering from such findings, she seemed to have Basedow's disease with associated features of Hashimoto's thyroiditis. In conclusion, we should bear in mind the possibility of Basedow's disease with associated features of Hashimoto's thyroiditis in subjects with Basedow's disease, particularly when TPOAb and TgAb as well as TRAb and TSAb are positive.