Background Visual analog scales (VAS) and Numerical Rating Scales (NRS) are commonly used to measure pain in rheumatoid arthritis.
Objectives To examine agreement between measurement of wrist pain by 100mm VAS and 11-point NRS and comparibility of responsiveness to treatment effects on wrist pain of both types of scales in patients with rheumatoid arthritis (RA).
Methods Data were used from a previously reported four–week randomized clinical trial on the efficacy of wrist working splints among 33 patients with RA suffering from wrist arthritis . Patients were randomly allocated to the splinting group (n=17) and the control group (n=16). The study demonstrated that wrist splints were highly effective in reducing wrist pain, assessed with 100 mm VAS, after four weeks of splint wearing. Average wrist pain during the past week was measured with a 100mm VAS (0-100) and a 11-point NRS (0-10). The scales were included on different places in a questionnaire, and the order of the scales was randomly varied between patients and between baseline and four-week measurement. Agreement between VAS and NRS to measure wrist pain was examined at baseline by Bland-Altman analysis. Preceding this analysis VAS pain scores were divided by 10 and rounded to the nearest integer to make them comparable to NRS pain scores. Differences in change scores on VAS and NRS between the splinting and the control group were analysed with analysis of covariance, and effect sizes (Hedges g) with corresponding 95% confidence intervals were calculated.
Results At baseline VAS and NRS pain scores were highly correlated (Pearson r=0.82). Mean difference between the VAS and NRS pain scores at baseline was -0.24 (SD=1.15). Bland-Altman analysis showed high individual variability between VAS and NRS pain scores with wide limits of agreement (- 2.49 to 2.01). Highly significant treatment effects were found on wrist pain measured by VAS (F(1,30)=11.1; P=0.002) and NRS (F(1,30)=9.1; P=0.005), and effect sizes for VAS (Hedges g= -1.24; 95%CI: -1.98 to -0.49) and NRS (Hedges g=-1.05; 95%CI: -1.78 to -0.33) were of similar magnitude and not significantly different as shown by the overlapping 95% confidence intervals.
Conclusions The high intra-individual variability in wrist pain measured by 100 mm VAS or 11 point NRS indicates that individual scores on VAS and NRS are not comparable. However, on a group level, VAS and NRS showed similar responsiveness to treatment effects of splint wearing on wrist pain in patients with RA.
Veehof MM, Taal E, Heijnsdijk-Rouwenhorst, van de Laar MAFJ. Efficacy of wrist working splints in rheumatoid arthritis: a randomized controlled study. Arthritis Care Res 2008; 59:1698-1704
Disclosure of Interest None Declared