Choosing the right outcome measures for acne scar research: a guide for clinicians

Acne scarring is a common consequence of acne vulgaris. Recently, there have been huge advancements in photoelectric therapies for scarring, leading to a growing body of literature on the efficacy and safety of these devices. However, interventional studies are hindered by the absence of standardized and validated outcome measures for acne scarring. In this article, we aim to review current grading modalities to assist clinicians in conducting acne scar research and therapies. PubMed and MEDLINE online databases were searched to identify acne scarring severity measurement tools. Each was classified into objective tools, subjective investigator-reported or patient-reported assessments and they were evaluated for reliability, sensitivity, validity and other important aspects. Objective instruments for assessing clinical efficacy in acne scarring show promise, especially PRIMOS, a three-dimensional imager with strong interrater reliability [intraclass correlation coefficient (ICC) > 0.90] and intrarater reliability (ICC > 0.96). Regarding subjective assessments, the Échelle d'Évaluation Clinique des Cicatrices d'Acné (ECCA) tool features the widest range of applications and shows acceptable performance. The original ECCA tool scored five out of eight points, while the adapted version achieved six out of eight points after combining three essential factors: reliability, sensitivity and validity. The Goodman and Baron Global Acne Scarring Grading System (GSGS) score also achieved a good score of seven out of eight. However, most scales demonstrated poor or moderate performance owing to the lack of reliability testing and evidence from independent assessment. Our conclusion is that PRIMOS stands out as a strong objective tool, whereas GSGS and adapted ECCA are the leading subjective scales with acceptable to strong performance. More importantly, there is the need for standardized scales, facilitating the pooling of results for systematic reviews, meta-analyses and clinical recommendations.