Hypersensitivity caused by synthetic thyroid hormones in a hypothyroid patient with Hashimoto's thyroiditis.

A 63-year-old hypothyroid woman with Hashimoto's thyroiditis developed fever, eosinophilia, and liver dysfunction in response to replacement doses of triiodothyronine, or L-thyroxine. The symptoms disappeared on cessation of the replacement therapy. Lymphocyte stimulation tests showed high stimulation indexes for both hormones. After an interval of four months, when the patient became severely hypothyroid, treatment with triiodothyronine on a slowly increasing dose program was tried and resulted in a good control without ill response at this time. This observation indicates that, under certain pathologic conditions, hypersensitivity may be induced to thyroid hormones administered exogenously.