Although the 308nm excimer laser has been shown to be both safe and effective for the treatment of plaque psoriasis,1 its application in this patient population has been limited by practical considerations. Currently, the laser is generally understood as being suited to manage patients with stubborn plaques over smaller body surface areas (mild psoriasis defined as less than three percent). Due to the limited power and spot size of previously available laser systems, treatment of patients with more than 10 percent body surface area was time consuming and generally impractical. However, a new excimer laser system, Xtrac Velocity (PhotoMedex) allows for more rapid treatment of larger surface areas. Ahead, Tina Bhutani, MD and John Koo, MD from the University of California, San Francisco Medical Center describe a protocol for the treatment of generalized plaque psoriasis using a new strategy involving laser in combination with specific topical agents.

How is it now possible to treat more extensive psoriasis with the excimer laser than could be treated in the past?
Dr. Bhutani is currently conducting a study of the Xtrac Velocity laser, which is 300-400 percent more powerful than its predecessor, the Xtac Ultra. This higher power permits more rapid treatment of larger surface areas. In fact, this study is specifically designed for patients with greater than 10 percent BSA involvment.

What would have taken up to 30 minutes with the Xtrac Ultra now is “multiples faster” with the Xtrac Velocity, Dr. Bhutani says. “We can treat 10 to 20 percent body surface area involvement in as little as 10 minutes.”

While the speed of treatment is important to make laser treatment of generalized psoriasis feasible, the targeted delivery of energy made possible with the use of the laser is also important. Fiberoptically-directed monochromatic UVB light as delivered via the excimer laser targets only psoriatic plaques, compared to traditional UVB and PUVA, which expose non-involved skin as well as psoriatic skin to UV light. What this means is that laser treatment of generalized psoriasis is not limited by the Minimal Erythema Dose (MED) or the minimum of ultraviolet light that causes normal appearing skin to turn erythematous. In traditional UVB or PUVA phototherapy, one cannot treat patients more aggressively than MED since to do so, by definition, would cause the patient to burn. The fact is, psoriatic plaque cannot only tolerate much more light than the MED, but more importantly, when psoriatic plaques are treated with multiples of the MED, it greatly enhances the efficacy of UVB compared to the traditional UVB usage.

Using the Xtrac Velocity, psoriasis patients typically improve markedly or clear in approximately 10 sessions instead of the 30 to 40 sessions usually required with regular full-body phototherapy. In comparison to internal options such as methotrexate or biologics, UVB phototherapy is similarly efficacious, but safer, Drs. Bhutani and Koo point out. The only real drawback of UVB phototherapy has been inconvenience. Dr. Bhutani states that this new approach with laser can possibly remove this only major weakness of UVB phototherapy.

Could you describe the treatment protocol to be used in the study?
The treatment protocol used in the pilot study includes three external therapeutic options: Clobex spray (clobetasol 0.05%, Galderma), Vectical ointment (calcitriol 3mcg/g, Galderma), and Xtrac Velocity laser. “This is an ‘external physics' approach rather than a ‘biochemical immunosuppressive' approach (i.e. biologics and oral options),” Dr. Bhutani observes. “This is an alternative to lifelong, whole body immunosuppression.”

All patients will use clobetasol spray twice daily for four weeks, followed by four weeks of treatment with topical calcitriol ointment twice daily. For the first six weeks of the strudy, each patient will receive excimer laser treatment twice per week for a total of 12 treatments. For patients with PASI 75 response or better at week 6, laser therapy becomes optional, depending on the activity of his or her psoriasis.

During weeks 8 through 12, all patients will use clobetasol spray BID and calcitriol ointment BID as a “booster” to optimize PASI response through week 12.

Dr. Bhutani refers to the protocol as a “perfect storm,” made possible by the advent of three external treatment options that are capable of covering a large body surface area conveniently with minimal systemic effects. A previous study with Xtrac Ultra has shown long duration of therapeutic effect, with 83 percent of patients maintaining at least PASI-50 24 weeks following the last treatment with laser.2

Are there limitations to this approach to psoriasis management?
Each component of the regimen is already FDA approved and on the market for treatment of psoriasis. Since this external approach may prove much safer than whole body immunosuppression, which is the mainstay of current approaches for generalized psoriasis, it maybe particularly beneficial for elderly and children with severe, generalized psoriasis, Dr. Bhutani suggests. The rapid progress and power of the laser technology permits treatment of large areas of involvement, making laser treatment an increasingly realistic option for individuals with significant BSA involvement. Although guttate, erythrodermic, and generalized pustular psoriasis or those with plaque psoriasis involving greater than 20-30 percent BSA will still be beyond the feasibility of this approach, it may still represent a valid alternative to internal agents for a large proportion of generalized psoriasis patients. Dr. Koo, who is the director of the UCSF Psoriasis Treatment Center and Professor and Vice Chairman of UCSF Department of Dermatology notes, “Most people think of lasers for localized, stubborn psoriasis. Most people don't think of laser for generalized psoriasis However, Dr. Bhutani's study aims to change that.”

“With this type of super aggressive UVB phototherapy that is termed ‘supra-erythemogenic' phototherapy, 3 it is possible to burn the psoriatic plaque if too much UVB irradiation is administered,” Dr Bhutani says. Therefore, the limit of aggressiveness with which “supraerythemogenic” phototherapy can be practiced is not MED but the MBD (Minimal Blistering Dose). If any burns occur, Dr. Bhutani recommends immediate application of clobetasol ointment preferably under impermeable occlusion. So far in this or the previous study,2 Koebner phenomenon has not been observed, but this may be due to immediate use of clobetasol ointment.

This protocol involving these particular three therapeutic options may prove not only additive in therapeutic effect, but possibly synergistic in minimizing risk. Since super aggressive UVB phototherapy can irritate the psoriatic plaque if one inadvertently goes beyond the threshold of plaque tolerance, the investigators hope that the simultaneous application of clobetasol spray allows greater margin of error by making phototoxic inflammatory reaction more difficult to be initiated. At the same time, the use of laser may decrease steroid exposure from clobetasol spray. Lastly, calcitriol, which is uniquely allowed to be used up to 200g/week and thereby useable for generalized psoriasis, will provide the necessary “steroid holiday” after the induction with laser and clobetasol spray.

Through skillful combination use of these three new external options—all applicable for widespread disease—this approach hopes to pioneer an alternative to possibly lifelong, systemic immunosuppression for a large proportion of patients with moderate to severe psoriasis, Dr. Bhutani concludes.