Psoriasis Challenge: pulsed dye vs. excimer lasers

New Orleans - According to Saleem Taibjee, M.D., both the xenon chloride excimer laser and the pulsed dye laser (PDL) can deliver long-term remission for localized plaque psoriasis. On average, the excimer is more effective; however, for a subset of patients, PDL treatment works better.

"Although the excimer laser has been specifically marketed for psoriasis, we have confirmed that the PDL, which tends to be much more widely available, is also a useful treatment option," says Dr. Taibjee, M.B. B.Ch., BMed. Sci., M.R.C.P.C.H., specialist registrar in dermatology.

With funding from Candela Laser Corporation, Dr. Taibjee and colleagues at Lasercare Clinics, City Hospital, Birmingham, England, conducted a head-to-head comparison of the two laser devices, following patients for one year.

Mean improvement in localized plaque severity index (PSI) was 4.7 with the excimer and 2.7 with the PDL. PSI improvement was significantly greater in excimer than PDL (p=0.003) or both control plaques (p<0.001). Clinical response to treatment, assessed by a comparison of baseline and endpoint photographs, indicated 13 patients responded best with excimer, two best with PDL and no difference for seven patients.

In using a SIAscope to take serial images of treated plaques, investigators also demonstrated that the lasers have different mechanisms of action. The PDL provoked a vascular-specific action characterized by blood vessel rupture and subsequent involution. The excimer, in contrast, produced a gradual diminution of vessels.

Side effects The most common side effect was blistering from the excimer.

"In 41 percent of patients, this was sufficiently severe to necessitate postponing one or more excimer treatments, despite cautious, stepwise increases in fluences. However, patients rarely found this distressing, and it tended to settle quickly," Dr. Taibjee says.

Hyperpigmentation was also common, occurring in 41 percent of excimer-treated plaques and in 9 percent of PDL-treated plaques. It resolved in all but one of the patients followed for a year. There were no instances of scarring.

Background Scientists have been investigating the use of laser therapy since the 1980's, and the efficacy of UVB phototherapy is well established. The excimer delivers high energy monochromatic UVB at 308 nm. Reported response rates for the treatment of psoriasis range from 69 percent to 85 percent. In some cases, remission lasts up to two years. By targeting lesional skin, the excimer reduces the cumulative dose and induces faster clearance. Patient satisfaction is high, but long-term side effects, including possible carcinogenesis, remain uncertain.

Previous studies evaluating the use of PDL devices for the treatment of psoriasis report 57 percent to 82 percent response rates with complete clearance in a subset of patients. Remission may extend to 15 months. Recent developments in PDL technology incorporate longer wavelengths, longer pulse widths, higher fluence and cryogen cooling.

Prior to this research, Dr. Taibjee notes, "The efficacy of second generation PDLs for treatment of psoriasis had not been established."

Methods To qualify for enrollment, patients had to be 18 or over with at least four discrete plaques (6 cm2 or larger) located on either the trunk or limbs. Exclusion criteria: known photosensitivity, pregnancy, greater than 20 percent total body surface area involvement, previous non-response to UV therapy or use of systemic therapy for psoriasis within the previous four weeks (six months for retinoids). Of the 22 patients enrolled, seven did not complete the full year of follow-up.

"If we exclude patients dropping out early," Dr. Taibjee says, "one worry is that we will overestimate the benefit of treatment. By bringing forward the last recorded measurements, as an approximation of final response, we were able to include these patients in the data analysis. This is important because, in real life, not all patients will finish their treatment."