Topical 8-methoxypsoralen increases the efficacy of narrowband ultraviolet B in psoriasis

Background: A combination of oral psoralen with narrowband ultraviolet B (UVB), defined as 'psoralen-narrowband UVB', was shown to have a superior efficacy than UVB alone and even a comparable efficacy to psoralen and ultraviolet A in psoriasis.
Objective: To find out whether topical psoralen-narrowband UVB provides any additional benefit to narrowband UVB alone in psoriasis.
Methods: Nineteen patients with plaque psoriasis were included. Phototherapy was given three times per week. Two symmetrical lesions were selected as target lesions. In the first 12 sessions of phototherapy, the target lesion on one side was treated with 1% 8-methoxypsoralen (MOP) gel 30 min before UVB radiation whereas the target lesion on the other side served as a control. Target lesion scores were assessed at baseline, third, sixth, ninth and 12th sessions. Side effects were recorded.
Results: Sixteen patients completed the study. Target lesion scores decreased significantly on both sides ( P <0.0001). The mean percentage of decreases was greater on the 8-MOP-applied sides compared with the control sides for all assessments, but the difference was statistically significant only at the ninth session (37.7% vs. 58.6%, P =0.043). Pigmentation was frequently seen in 8-MOP gel-applied lesions.
Conclusion: Topical 8-MOP gel plus narrowband UVB has greater efficacy than narrowband UVB alone in psoriasis.