Ultraviolet B 308-nm excimer laser treatment of psoriasis: a new phototherapeutic approach.

BACKGROUND

Excimer laser-derived 308-nm ultraviolet (UV) B therapy is a new alternative for treating psoriasis by phototherapy. Some studies have been made showing the effectiveness of intralesional phototherapy technology in treating psoriasis. However, there has been no information available so far with regard to the cumulative dosage on a larger group of patients and on therapy optimized treatment strategies.

OBJECTIVES

One hundred and twenty psoriatic patients were treated according to standard protocol to define the effectiveness. Our aim was to develop new parameters and determine whether effectiveness could be improved and whether treatment exposure, the cumulative UVB dose and adverse effects could be minimized.

METHODS

Initially, the excimer laser's effectiveness in treating psoriasis was evaluated in an open prospective study according to standard protocol. This included 120 adult patients (67 female/53 male) with chronic plaque psoriasis and < 20% involved body surface. The initial dose was based on three multiples of a predetermined minimal erythema dose (MED). Patients were treated twice a week for the first 3 weeks, then once a week until clearance was achieved. The main parameters were the initial starting dose, psoriasis area and severity index (PASI), the number of treatments needed, the time in treatment and the cumulative dose needed to clear psoriatic plaques. Thereafter, 43 patients were treated as a second comparable group. Therapy began with a starter dose, defined as MED-I. MED-I was defined as a UVB 308-nm dose which provoked a visible increase in erythema after 24 h. In addition, the epidermal thickness of the plaques was measured on an individual basis by 20-MHz ultrasound and correlated to the MED-I.

RESULTS

Of the patients who met the standard protocol, 65.7% were at least 90% clear after a maximum of 10 treatments; an even greater number (85.3%) showed a > or = 90% improvement in PASI after 13 sessions, while 14.7% of patients had only a < or = 50% PASI improvement. The cumulative UVB dose was 11.25 +/- 4.21 J cm-2 and the average treatment time was 7.2 weeks. Patients treated individually with the MED-I starter dose showed nearly identical rates of clearance (83.7%), but were clear in 7.07 +/- 2.15 sessions with a cumulative dose of 6.25 +/- 4.02 J cm-2.

CONCLUSIONS

The majority of our patients benefited greatly from laser-derived 308-nm UVB therapy, which cleared skin lesions faster than conventional phototherapy. As this therapy targets only the involved skin, the thickness of the plaques and individual MED-I should determine the initial dose, thus increasing the effectiveness of the therapy. We propose that light therapy sparing uninvolved skin will become predominant in the future.