Treatment of hypertrophic scars and keloids by fractional carbon dioxide laser: a clinical, histological, and immunohistochemical study

Treatment of keloids (K) and hypertrophic scars (HTS) is challenging. A few case reports reported good results in HTS treated by fractional CO₂ laser. The aim of the present study was the assessment of the clinical response as well as histological changes in K and HTS treated by fractional CO₂ laser and the role of matrix metalloproteinase 9 (MMP9) in the response. A randomized half of the scar was treated by fractional CO₂ laser in 30 patients (18 K, 12 HTS) for a total of four sessions 6 weeks apart. Vancouver scar score (VSS) was done before and 1, 3, and 6 months after the last laser session by a blinded observer. Biopsies taken from normal skin, untreated scar, and treated scar tissue 1 and 3 months after the laser sessions were stained by HX & E for histological changes and Masson trichrome for collagen fiber arrangement. Immunohistochemical staining for MMP9 was done in before and 1 month after samples. Quantitative morphometric analysis was done for collagen and MMP9 by image analyzer. Nineteen patients completed the 6-month follow-up period (12 K, 7 HTS). VSS score was significantly lower in the treated compared to untreated areas after 3 and 6 months in both K and HTS but was mainly due to improved pliability of the scar. Histologically, dense inflammatory infiltrate and increased vascularity was apparent 1 month after laser sessions and disappeared at 3 months. Thinner better organized collagen bundle could be seen in 3 months after samples. MMP9 was significantly increased in after treatment samples but without significant correlation with VSS. Fractional CO₂ resurfacing is safe but affects mainly pliability of K and HTS with collagen remodeling apparent 3 months after therapy. MMP9 may play a role in mechanism of action of CO₂ laser in K and HTS.