Effect of propylthiouracil on adenosine deaminase activity and thyroid function in patients with psoriasis

T-cell activation has been implicated in the pathogenesis of psoriasis; adenosine deaminase (ADA) activity has been considered as a marker of T-cell activation. The antithyroid drug propylthiouracil (PTU) has recently been shown to have beneficial effects on psoriatic lesions, probably by acting on the immune system.

To investigate whether ADA activity may be related to psoriasis and whether oral PTU affects ADA activity and gives clinical improvement in psoriatic patients.

ADA activities were measured in plasma, erythrocyte and tissue samples of patients with psoriasis before and after 2 months of treatment with either PTU 100 mg three times daily or PTU plus thyroxine 25 microg once daily (to prevent possible hypothyroidism, which may be induced by PTU) as well as in healthy controls. The severity of the disease was evaluated before and after treatment according to Psoriasis Area and Severity Index (PASI) scores. Routine analyses and thyroid function tests were also carried out during the study.

All patients showed significant clinical improvement in their lesions and decreased PASI scores after the treatments. Elevated baseline ADA activities in skin and plasma were found to be lower, and decreased baseline erythrocyte ADA was higher, after the treatments in all patients, and they were not different from control values. Although thyroid function tests were not affected by the treatments, serum thyroid-stimulating hormone levels were found to be higher after the treatments, and there was a larger increase in patients treated with PTU alone. However, none of the patients had clinical hypothyroidism or cytopenia.

ADA activity may be clinically useful for indicating T-cell activation in psoriasis. Because of its antiproliferative and immunomodulatory effects, antioxidant potential and low toxicity, PTU may be an effective agent in the treatment of psoriasis.