308-nm excimer laser for the treatment of psoriasis: a dose-response study

OBJECTIVE: To determine the dose-response relationship of excimer laser-generated 308-nm UV-B radiation for treating psoriasis. DESIGN: Pilot study with a before-after design. SETTING: A university dermatology service. PATIENTS: Thirteen consecutive patients with at least 4 large, stable psoriasis plaques. INTERVENTIONS: Excimer laser-generated 308-nm UV-B radiation was given to each of 4 plaques, which received 1, 2, 4, and 20 treatments, respectively. Untreated areas within each plaque served as controls. Within each plaque, 8 doses based on multiples of a predetermined minimal erythema dose (MED) were tested in distinct sites. The multiples were 0.5 and 1 (low dose); 2, 3, 4, and 6 (medium dose); and 8 and 16 (high dose). At every treatment, the dose for each site remained fixed at the same MED multiple. A psoriasis severity index score was determined for each area before, every 2 weeks during, and 2 and 4 months after treatment. RESULTS: The mean+/-SD MED was 203.03+/-57.84 mJ/ cm2. Treatment with high fluences produced significantly better results than that with medium and low fluences at weeks 4, 6, 8, and 10 (P<.05). At 4 months' follow-up, all sites that received low or medium fluences had recurrences, whereas those that underwent a single treatment at 8 and 16 MED multiples remained in remission. CONCLUSIONS: With 308-nm UV-B radiation generated by an excimer laser, it is possible to clear psoriasis with as little as 1 treatment with moderately long remission. In contrast to traditional phototherapy techniques, this handheld excimer laser UV-B therapy is selectively directed toward lesional skin, thus sparing the surrounding normal skin from unnecessary radiation exposure. Treatment of other inflammatory diseases and limited psoriasis seems reasonable to pursue with this modality.