Which factors explain the patient global assessment in patients with ankylosing spondylitis? A hierarchical cluster analysis on REGISPONSER-AS.

OBJECTIVES: To determine groups of factors (clusters) potentially associated with the patient global assessment (measured with the Bath Ankylosing Spondylitis Patient Global Score (BAS-G)), and to quantify the contribution of each cluster to the patient's well-being. METHODS: This was a cross-sectional study in patients with a diagnosis of ankylosing spondylitis (AS) from the national, multicentre Spanish REGISPONSER-AS registry. A hierarchical cluster analysis was conducted to group the potential factors (sociodemographic, socioeconomic, patient-reported outcomes, physical exploration variables and depression) associated with the BAS-G. The contribution of each cluster to the variability of the BAS-G was evaluated using a multivariate linear regression model and the determination coefficient (R2) for each cluster. RESULTS: A total of 681 patients with complete data were included. Three clusters of variables potentially associated with the BAS-G were found: cluster 1 contained the Maastricht Ankylosing Spondylitis Enthesitis Score (MASES), depression, sex (female) and university studies; cluster 2 included the Graffar scale, age and body mass index; and cluster 3 contained the Bath Ankylosing Spondylitis Functional Index (BASFI), the individual items of the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), pain during the last week, nocturnal pain and the number of swollen joints. A total of 6.8% of the variability of the BAS-G was explained by cluster 1, 0.5% was explained by cluster 2, and 60.8% was explained by cluster 3. CONCLUSION: The BAS-G is mostly explained by pain and function, while demographic and socioeconomic factors are weakly associated with the BAS-G. Depression also has a weak effect on this score.

ASAS Health Index in patients with spondyloarthritis and its association with disease activity and disease burden including fibromyalgia.

OBJECTIVES: To evaluate the association of the Assessment of Spondyloarthritis international Society Health Index (ASAS-HI) with disease activity and disease burden in patients with spondyloarthritis (SpA). METHODS: Observational, cross-sectional and single-centre study from the Córdoba AxSpA Task force, Registry and Outcomes (CASTRO). Scores related to disease activity (BASDAI and ASDAS), functionality (BASFI), structural damage, mobility, health and the presence of concomitant fibromyalgia (FM) were obtained from all patients. ASAS-HI score was considered the main outcome. Pearson's r statistic, Student's t test, and univariate and multivariate linear regressions were performed to assess the association between the ASAS-HI score and the studied covariates. RESULTS: A total of 126 SpA patients were included. The mean ASAS-HI score was 4.6±3.9, showing a "strong" positive linear correlation (r>0.60) with the BASDAI and BASFI and a "moderate" positive linear correlation (r=0.40 to 0.60) with the global VAS and ASDAS. Patients with FM showed a significantly higher ASAS-HI score than patients without FM (9.5±3.2 vs. 3.7±3.4, respectively, p<0.01). Multiple linear regression showed that 57.4% of the ASAS-HI variability (R2=0.574) was explained by the presence of concomitant FM (ß=2.23, 95% CI 0.73 to 3.80, p=0.004), higher scores on the BASDAI (ß=0.62, 95% CI 0.25 to 0.97, p=0.001) and BASFI (ß=0.57, 95% CI 0.26 to 0.88, p=0.001). CONCLUSIONS: The impairment of health in patients with SpA was mainly associated with high disease activity, worsening functionality and with the presence of a possible concomitant FM. Therefore, in patients with high ASAS-HI scores we must evaluate the presence of concomitant FM.