Oral propylthiouracil for the treatment of resistant plaque psoriasis

BACKGROUND: Propylthiouracil (PTU) has been used in the treatment of hyperthyroidism for many years and inhibits the enzyme 5'-deiodinase, which converts thyroxine to triiodothyronine. Several studies have reported PTU as an effective treatment for plaque psoriasis. PTU exhibits immunomodulatory effects; however, its exact mechanism of action in psoriasis is unknown. Few patients were studied in these reports and treatment with PTU was continued for no longer than 8 weeks. METHODS: In this study we report on four patients with resistant plaque psoriasis who had treatment with oral PTU for 4-32 weeks (mean 18.4). RESULTS: Three of the four patients exhibited moderate clinical improvement with reductions in psoriasis severity observed within 4-6 weeks of commencing PTU therapy. The side effects noted were subclinical hypothyroidism in two patients and worsening of muscle aches in one patient. Monitoring included regular thyroid function, full blood count, and liver and renal function tests. CONCLUSION: This study illustrates that oral PTU can be a useful addition to the therapy of resistant cases of plaque psoriasis and shows that this treatment can be continued for longer than 8 weeks with few side effects occurring secondary to PTU.