Treatment of Plaque Psoriasis With an Excimer Laser Utilizing an Optimal Therapeutic UVB Dose Protocol

April 2020 | Volume 19 | Issue 4 | Original Article | 349 | Copyright © April 2020

Published online March 27, 2020

Quinn Thibodeaux MD,a Kristen Beck MD,a Benjamin N. Lockshin MD,b Neal Bhatia MD,c Ethan Levin MD,a John Koo MD,a and Tina Bhutani MDa

aDepartment of Dermatology, Psoriasis & Skin Treatment Center, University of California, San Francisco, San Francisco, CA bClinical Trials Center at DermAssociates, US Dermatology Partners, Rockville, MD cTherapeutics Clinical Research, San Diego, CA

Background: Traditionally, treatment with the excimer laser requires determining the minimal erythema dose on healthy skin or using plaque-based induration; however, these protocols often lead to underdosing of psoriatic plaques and reduced treatment efficacy.
Objective: To prospectively evaluate the effect of the excimer laser on plaque psoriasis using an optimal therapeutic dose (OTD) protocol. Methods: Subjects with stable plaque psoriasis were tested with the Multi-Microdose (MMD) tip on the XTRAC excimer laser to determine a minimum blistering dose (MBD). Treatment was then initiated at 20% less than the MBD. A single psoriatic lesion was treated once weekly for up to 11 sessions. The change from baseline of the target lesion's modified psoriasis area severity index (mPASI), quality of life and safety were evaluated.
Results: Thirteen subjects with a mean age of 48.9±14.9 years and Fitzpatrick skin types I-IV participated in the study. Target plaque mPASI significantly decreased at all time points relative to baseline with significant improvement by the second treatment. Patients reached mPASI-75 within 5±2 sessions. By the end of the study 92% of patients achieved mPASI-75. On average, patients maintained an mPASI score ≥50% for 60 days. Treatment was well tolerated with no erosions or hyperpigmentation. Erythema was the most common adverse event.
Conclusion: The OTDTM protocol with the MMD® tip allows determining the optimal dose locally on the psoriatic plaque itself. Consequently, ineffectual dosing levels and treatments are minimized. The OTD protocol reduces treatment frequency from 2-3 times per week to once weekly.

J Drugs Dermatol
. 2020;19(4):349-354. doi:10.36849/JDD.2020.4891


Psoriasis is a chronic, immune-mediated disease with prevalence estimates within adult populations ranging from 0.91% in the USA to 8.5% in Norway.1 The disease mainly affects the skin and joints and has several phenotypes, of which the most common is psoriasis vulgaris (plaque-type psoriasis).2 Psoriasis vulgaris typically presents as well-defined, symmetric, erythematous scaly plaques on the scalp, trunk, nails, and extremities. Symptoms include itching, burning and soreness.3

The treatment approach for psoriasis depends on disease severity (defined by the percentage of affected body surface area), involved body areas, comorbidities, age, patient preference (including cost and convenience), and individual patient response to therapy.3,4 Limited psoriasis can often be managed with topical agents, while patients with moderate to severe disease may also need phototherapy by ultraviolet irradiation or systemic therapy.5 During phototherapy treatments, therapeutic doses of ultraviolet light may be administered by broadband ultraviolet B (UVB) radiation (290-320 nm), narrowband UVB (311-313 nm), and PUVA - photochemotherapy with psoralen followed by ultraviolet A radiation (320-400 nm).6,7

In targeted phototherapy, a high-energy 308 nm excimer laser delivers ultra-narrowband-UVB directly to the psoriasis plaque with minimal exposure of healthy skin to UVB radiation. Due to the targeted nature of the excimer laser, considerably higher doses of UVB can be administered at each treatment session when compared with traditional phototherapy since dosing is not limited by the lower light tolerance of healthy skin.8

Dosimetry for phototherapy with the excimer laser has been traditionally determined either through the induration protocol, which takes into account the patient’s Fitzpatrick skin type and the degree of plaque induration,9 or through the minimal