A cross-sectional pilot study evaluating the histopathology of atrophic acne scars with a focus on the vertical depth of ice pick, boxcar, and rolling scars and its implications in skin of colour

Background Atrophic acne scars are clinically classified as rolling, icepick, or boxcar, but there is scarce data on the histopathology and depth of these scars, particularly in skin of colour. Objectives Our objective was to assess the histological changes in atrophic acne scars and determine the vertical depth of each scar type. Methods A total of 32 boxcar, 10 ice-pick, and 7 rolling scars were biopsied. Tissue samples were stained with haematoxylin and eosin, Verhoeff-van Gieson, and Masson's trichrome stains. Acne scars were identified based on morphological changes in collagen and elastin, loss of pilosebaceous units in the scar area, and tilting of follicular units in the adjoining dermis. The depth of the scars was measured in µm. Results Atrophic acne scars revealed loose, haphazardly arranged collagen (71%) and reduced elastic tissue (96%). Appendageal tilting was noted in 44/49 (90%) biopsies, with consistent pilosebaceous unit loss in the scar. Mean depths of ice-pick, boxcar, and rolling scars were 1933.4 ± 1117.8 µm, 1327.88 ± 571.34 µm, and 1357.14 ± 578.3 µm, respectively. There was a significant difference in the mean depth of scars between ice-pick and boxcar scars (p=0.02). Additional findings noted were scar vascularisation (n=46), ectatic channels in the scar (n=18), mononuclear inflammatory infiltrates (n=43), calcinosis (n=3), demodex mites (n=2), solar elastosis (n=2), pigment-laden macrophages (n=2), granulomatous perifolliculitis (n=4), and pulled up eccrine glands (n=8). Based on existing data, the dose of fractional carbon dioxide (Fr: CO2) laser should be set to achieve an approximate depth of 1933.4 µm to address all atrophic scars. Limitations Small sample size and technical difficulties in histological sectioning of atrophic scar remain the main limitations of our study. Conclusion This study provides novel histological insights into facial atrophic acne scar characteristics and depth in skin of colour. Also, it gives data on the histological depth that needs to be achieved by energy devices, using the appropriate dose based published data.