Background The Assessment of SpondyloArthritis international Society (ASAS) has selected core sets of variables to include as standardised end points in clinical trials and clinical practice. These core sets include fatigue, pain and patient global assessment (PaGl) as key patient-reported outcome measures (ref.). However, although associations between fatigue, pain and PaGl have been examined to some extent on the group level, studies focusing on the agreement between these patient-reported measures in individual patients are missing. A better understanding of how tight the measures are bounded in individuals may improve our ability to deal with them in the daily clinic.
Objectives To examine associations on the group level and agreements on the individual patient level between fatigue, pain and PaGl as scored on visual analogue scales (VAS) in the daily clinic by patients with active spondyloarthropathy (SpA).
Methods Data on 118 SpA patients with active disease planned to initiate treatment with a biological agent were extracted from the Danish registry for biological treatment in rheumatology (DANBIO). Data included fatigue, pain and PaGl, BASDAI and BASFI assessed on VAS-scales (0–100) and age, CRP and physician global assessment. Associations between variables were examined using simple and multiple regression analysis (all mentioned variables including sex was incorporated as independent variables). Agreements between PaGl, pain and fatigue on the individual patient level was examined by Bland-Altman analyses yielding 95% lower and upper limits of agreement (LLoA and ULoA) between intra-individual assessments. The difference between the scores on the group level was expressed as the bias.
Results Mean age was 42.9±12.6 years, mean BASDAI 56.0±19.0, mean CRP mg/dL12.9 and mean PaGl 65.7±22.6. No significant differences in BASDAI, fatigue, pain, PaGl were demonstrated between men (n=76) and women. Fatigue, pain and PaGl were significantly but only moderately inter-correlated with high standard errors of estimation (SEE): Fatigue vs. PaGl (r =0.57, p<0.0001, SEE =21.4), fatigue vs.pain (r =0.55, p<0.0001, SEE =21.6), and pain vs. PaGl (r =0.81, p<0.0001, SEE =15.1). In multiple regression analyses, pain was independently predicted by PaGl (beta =0.52, p<0.0001) and BASDAI (beta =0.36, p<0.0001) [R =0.82, SEE =14.1, p<0.0001], PaGl by pain (beta =0.54, p<0.0001) and BASDAI (beta =0.33) [R =0.81, SEE =12.7, p<0.0001]), and fatigue by BASDAI (beta =0.44, p<0.0001) and PaGl (beta =0.23, p<0.05) [R =0.63, SEE =20.2, p<0.0001]. Biases between the patient-reported VAS-scores were small but intra-individual differences were substantial: LLoA and ULoA [bias] for fatigue vs. PaGl were -45.5 and 43.5 [-0.97], for fatigue vs. pain -42.3 and 52.9 [5.3], and for pain vs. PaGl -35.7 and 23.3 [-6.3]. LLoA and UloA remained constant over the whole range of the VAS-scales.
Conclusions In patients with SpA, fatigue, pain and PaGl scores were poorly associated and only poorly explained by other potential explanatory variables. On the individual level, disagreements between the scores were substantial. The findings emphasize the complexity of understanding patient-reported outcome measures and their diverging interplay across individuals.
van der Heijde D et al. J Rheumatol 1999; 26: 951–4.
Disclosure of Interest None declared