The effect of steroid therapy on Riedel's thyroiditis

A patient is described who passed from a clinical state consistent with Hashimoto's thyroiditis to Riedel's thyroiditis over a period of 6 months. Serum levels of thyroid antibodies were high and there was a family history of Hashimoto's thyroiditis. A good therapeutic response to steroids was observed but these were without effect in a further patient with Riedel's thyroiditis of 10 years' duration. It is suggested that Riedel's thyroiditis is an uncommon variant of Hashimoto's thyroiditis.