Clinical usefulness of a long-term treatment with an antithyroid drug for psoriasis vulgaris.

We have previously reported that an antithyroid thiourethylene, thiamazole, can bring about significant clinical improvement in patients with psoriasis vulgaris. Although the efficacy of antithyroid thiourethylenes had been reported earlier, few studies have evaluated the safety of its long-term use. In this study, we aimed to study whether or not long-term thiamazole administration is complicated by any adverse effects. Eight patients with psoriasis vulgaris were enrolled in this study after informed consent was obtained. Each patient was administered thiamazole orally at 30 mg/day for 12 weeks. Two patients achieved complete clearance of psoriatic lesions. Four patients showed a significant improvement, and two patients did not reach satisfactory improvement. Some adverse effects developed in five patients; serum TSH levels elevated above the normal range in three patients and fell below the normal range in one patient. However, serum free-T3 and free-T4 levels remained within normal ranges during the treatment in all patients, and none of the patients developed clinical hypothyroidism. This preliminary study suggests that thiamazole administration is an effective and relatively safe treatment for patients with psoriasis vulgaris.