Comparing the visual analogue scale (VAS) and the numerical rating scale (NRS) in patient reported outcomes in psoriatic arthritis

Objective Patient self-report scales are invaluable in psoriatic arthritis (PsA), as they allow physicians to rapidly assess patient perspectives of disease activity. We aimed to assess the agreement of the visual analogue scale (VAS), a 100 mm horizontal line, and the numerical rating scale (NRS), a 21-point scale ranging from 0 to 10 in increments of 0.5, in patients with PsA.

Methods Data were collected prospectively across three UK hospital trusts from 2018-2019. All patients completed the VAS and NRS for pain, arthritis, skin psoriasis, and global disease activity. A subset completed an identical pack one week later. Demographic and clinical data were also collected. Agreement was assessed using medians and the Bland-Altman method. Intraclass correlation coefficients (ICC) were used to assess test-retest reliability. Spearman’s rank correlation coefficients were used to assess dependency between scale scores and clinical parameters.

Results 210 patients completed the study; one withdrew consent, thus 209 were analysed. For pain, arthritis, skin psoriasis and global disease activity, the difference between the VAS and NRS mostly lay within 1.96 SD of the mean, suggesting reasonable agreement between the two scales. 64.1% patients preferred the NRS. The ICCs demonstrate excellent test-retest reliability for both VAS and NRS. Higher VAS and NRS scores were associated with increased tender/swollen joint count, poorer functional status and greater life impact.

Conclusion The VAS and NRS show reasonable agreement in key patient reported outcomes in PsA. Results from both scales are correlated with disease severity and life impact.