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Split‐lesion comparison of long and short pulses for pulsed dye laser treatment of scars

Pulsed dye lasers (PDLs) are commonly used for the treatment of vascular lesions and are effective treatment options when used to limit or prevent scarring [ 1–3 ] . However, the optimal parameters of PDLs are unclear. Many dermatologists prefer short-pulse PDLs with low fl uence for scar treatment and have demonstrated clinical improvement of hypertrophic scars [ 4–6 ] . However, purpura and brown discoloration lasting for 2–4 weeks may occur after short-pulse PDL treatment, and can limit the use of short-pulse PDLs [ 7 ] . Long-pulse PDL could be used for scar treatment in order to avoid post-treatment purpura. However, it is not yet clear whether there are differences in the effi cacy of short and long pulse PDLs for scar treatment. In this study, we used objective methods such as skin assessment devices to compare the effects of short and long pulse durations on scars. Ten outpatients with post-thyroidectomy scars following thyroidectomy for early stage thyroid cancer were enrolled in this prospective study after approval from the Severance Hospital Institutional Review Board (1-2014-0006). The scars were divided into two equal portions (right and left) separated by a non-treated area 1 cm in width. The right and left sides underwent PDL treatment (585 nm, 8 J/cm 2 , 7 mm spot size) with a short pulse duration (1.5 ms) and a long pulse duration (10 ms), respectively. Three laser sessions were scheduled at three-week intervals and the outcomes were evaluated using the Vancouver scar scale (VSS) as well as a Cutometer ® and a Mexameter ® . Evaluations were performed before each treatment and six weeks after the last treatment (Figure 1 a, b). The statistical signifi cance of improvements compared to baseline that were noted at each visit was assessed with the Wilcoxon signed-rank test. Differences in improvements between the two groups were evaluated with the aid of the Mann-Whitney test. The mean patient age was 37.2 ± 5.2 years, and eight of the ten patients were female. All patients had Fitzpatrick skin type III or IV. The mean length of the scars was 8.1 cm (range: 4.3–14.9 cm). Although all VSS parameters (except thickness) improved over time in both groups (thickness did not change over time in either group), pliability was the only factor that was signifi cantly better after long-pulse than short-pulse PDL treatment. The total VSS scores improved signifi cantly over time in both groups (Figure 2 ). Elasticity as measured with a Cutometer ® also improved in both groups. Interestingly, short-pulse treatment improved the vascularity score more than long-pulse treatment, but the reverse was found for the pigmentation score. This pattern was reproduced for the erythema and melanin indices measured with a