Validation of the Physician's Global Assessment of Fingernail Psoriasis by Rheumatologists Treating Psoriatic Arthritis.

OBJECTIVES: This study aimed to assess the content validity and reliability of the Physician's Global Assessment of Fingernail Psoriasis (PGA-F) by rheumatologists treating patients with psoriatic arthritis. METHODS: There were 3 stages of analyses with 3 clinician cohort groups. Stage 1 (concept confirmation) included rheumatologist qualitative data (cohort 1) to establish content validity, acceptability, utility, and feasibility of the PGA-F in assessing nail severity. Quantitative information regarding the response category utilization in nail abnormalities was assessed by photographs. Stage 2 (inter-rater reliability) involved quantitative analysis of PGA-F data from study investigators, including rheumatologists, involved in a phase III clinical study (cohort 2) and a cohort of newly recruited rheumatologists (cohort 3). Stage 3 included known-groups validity. RESULTS: Qualitative analyses identified consensus that the PGA-F severity levels are comprehensive of real-world patient symptoms and the instrument is simple to use and understand. Psychometric analyses support the PGA-F as a clinical outcome assessment tool. Inter-rater reliability showed rheumatologist agreement across the fingernail psoriasis severity spectrum. They were monotonically ordered by the hypothesized severity structure with excellent fit to the clinicians who evaluated them. Agreement on the rank order of the severity of the photographs in this target rheumatologist population was consistent with previous reports by dermatologists. CONCLUSIONS: The PGA-F was shown to be usable by rheumatologists to measure patients along the full range of the fingernail psoriasis severity spectrum, have a strong relationship with a conceptually similar reference measure, differentiate among patients based on fingernail psoriasis severity, and detect category severity change over a 24-week period.