The Static Physician's Global Assessment of Genitalia: A Clinical Outcome Measure for the Severity of Genital Psoriasis

Introduction: Genital psoriasis is a common but frequently overlooked manifestation of psoriasis with a considerable impact on patients' quality of life. Currently no validated clinical trial outcome measures exist to assess genital psoriasis severity that meet regulatory agency requirements. Methods: This study describes the development of the static Physician's Global Assessment of Genitalia (sPGA-G) scale, a clinical outcome measure for the assessment of genital psoriasis severity that accounts for the erythematous clinical presentation of genital psoriasis. The reliability of the sPGA-G was evaluated using scores collected from clinician assessments of photographs of genital psoriasis cases. Scores were collected from 10 academic and clinical experts in genital psoriasis and 95 clinician assessors who participated in either in-person (n=28) or online (n=67) sPGA-G training modules. Results: The sPGA-G had a high inter-rater reliability (IRR, measured by Kendall's W) for expert raters (W=0.856, P<0.0001), in-person assessors (W=0.822, P<0.0001), and online assessors (W=0.678, P<0.0001). IRR was also high for all clinical assessors combined, (W=0.714, P<0.0001). Discussion: This study demonstrates that the sPGA-G is an intuitive and reliable clinical outcome measure that specifically measures the severity of genital psoriasis.