An episode of silent thyroiditis in a patient with chronic thyroiditis and papillary adenocarcinoma following alpha interferon treatment for hepatitis C.

In the present paper we described the first case report of silent thyroiditis following alpha-interferon (IFN-alpha) treatment for chronic type C hepatitis in Japan. A 51-year-old woman with chronic type C hepatitis was treated with 6 million units of IFN-alpha three times a week for 24 weeks. Thyroid function was within normal limits and thyroid autoantibodies were negative before IFN therapy. Sixteen weeks after initiation of the treatment, she complained of increasing fatigue, palpitation and losing 7 kg in weight. Thyroid function tests at that time revealed an increase in serum T3, T4, free T3 and free T4 and a markedly suppressed TSH concentration. Both antithyroglobulin antibody (TgAb) and antimicrosomal antibody (McAb) were positive in a dilution of 1: 400. The computed tomographic (CT) scan of the thyroid showed a decrease in the CT number (Hounsfield unit; H.U.) to 58 H.U. (normal, 95-167 H.U.). The 24-h thyroid uptake of 123I was 0.75%. Aspiration biopsy specimens from a nodule in the right lobe and the remaining struma disclosed papillary adenocarcinoma and Hashimoto thyroiditis, respectively. Thyroid function spontaneously returned to normal two months after the onset of thyrotoxicosis through the subclinical hypothyroid stage. After recovery of thyroid function, patient had an operation of papillary cancer without any complications. These clinical features and laboratory findings led to the diagnosis of silent thyroiditis developing in the course of the long-term IFN therapy, which, to our knowledge, has not been reported before in Japan.