Pathological characteristics of acute exacerbation of Hashimoto's thyroiditis--serial changes in a patient with repeated episodes.

A 76-year-old female patient with known Hashimoto's thyroiditis had 12 episodes of acute exacerbation, characterized by high fever and spontaneous pain in the thyroid over a period of 4 months. Percutaneous needle biopsies were performed before and serially after local steroid injection. Histological examination of the thyroid tissue involved obtained before steroid administration revealed quite a unique localized edematous and inflammatory appearance with rich but loosely arranged collagen fibers, and destruction of follicular structures and swollen degenerated epithelia. Neither remarkable cellular infiltrations nor granulomatous changes were observed in the area involved. Ultrasonogram showed an extremely hypoechoic lesion coincident with the location of pain and tenderness. Intrathyroidal administration of triamcinolone acetate (40 mg) resulted in an immediate relief of pain, fever and localized swelling. Surprisingly, remarkable histological improvements were observed even on the day following the injection. However, clinical manifestations as well as histological changes were reversed again within one week or so. After various therapeutic means, total thyroidectomy was performed which induced disappearance of the manifestations. The etiology remains unclear, but pathological findings observed in this patient may provide an insight into the pathogenesis of this rare but intractable condition.