Effect of Eetinoic Acid in Psoriasis

The effect of topical retinoic acid on the clinical and histological features and mitotic counts of lesions in 12 patients with psoriasis have been studied for a 2‐week period. Serial biopsies were performed on lesions treated with retinoic acid in all 12 patients; control lesions treated with unmedicated ointment base were similarly biopsied in 7. There was a significant clinical improvement in 11 of the 12 patients treated with retinoic acid, and in all these patients it was greater than that achieved in the control lesions. Reformation of the granular layer, which was previously absent or only partially formed, occurred in 6 of the 12 psoriatic lesions treated with retinoic acid, but in none of the controls. Mitotic counts for the treated group fell after the 2‐week period, but not in the controls. Topical retinoic acid would seem to be of therapeutic value in the treatment of psoriasis. The possible mechanisms of action are discussed.