Oral propylthiouracil for the treatment of resistant plaque psoriasis

BACKGROUND: Propylthiouracil (PTU) has been used in the treatment of hypert hyroidism for many years and inhibits the enzyme 5 ' -deiodinase, which con verts thyroxine to triiodothyronine. Several studies have reported PTU as a n effective treatment for plaque psoriasis. PTU exhibits immunomodulatory e ffects; however, its exact mechanism of action in psoriasis is unknown. Few patients were studied in these reports and treatment with PTU was continue d for no Ion-er than 8 weeks. METHODS: In this study we report on four patients with resistant plaque pso riasis 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 commenc ing PTU therapy. The side effects noted were subclinical hypothyroidism in two patients and worsening of muscle aches in one patient. Monitoring inclu ded regular thyroid function, full blood count, and liver and renal functio n tests. CONCLUSION: This study illustrates that oral PTU can be a useful addition t o the therapy of resistant cases of plaque psoriasis and shows that this tr eatment can be continued for longer than 8 weeks with few side effects occu rring secondary to PTU.