Background/Purpose: Juvenile-onset Spondyloarthritis (JSpAs), referred to as Enthesitis-Related Arthritis (ERA) subtype under the International League of Associations for Rheumatology (ILAR) classification is characterized by arthritis and enthesitis largely affecting the lower limbs.  Axial involvement is uncommon at presentation, but may develop later in life. Although there are validated instruments assessing spinal disease in adults with Ankylosing Spondylitis (AS) such as the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Bath Ankylosing Spondylitis Functional Index (BASFI), there are no validated tools to measure disease activity or functional impairment in this population of children. We have previously reported excellent intra-rater reliability of the BASDAI and BASFI. The aims of the current study were to measure the validity and responsiveness of these two adult scores in ERA.

Methods: Patients diagnosed with ERA followed in the JSpA Clinic at The Hospital for Sick Children (June 2009 – June 2010) were enrolled into the study.  The BASDAI and BASFI were measured prospectively at baseline and again at 4 to 6 months.  At each study visit, joint and entheseal clinical exams were performed according to a standardized protocol. The data collected at baseline and follow up visit were used to assess construct validity and were expressed using Pearson’s correlation coefficient. Responsiveness (sensitivity to change) was calculated in a subgroup of patients who showed changes in their joint and entheseal counts over time by dividing the mean change between the two assessments by the standard deviation of the change scores and was expressed by effect size.

Results: There were 41 patients (85% male) with a mean age at diagnosis of 12.1 ± 7.6 years and average age at enrollment of 14.5 ± 2.5 years.  Average disease duration at the time of the study was 5.1 ± 2.4 years. 46% were HLA B27 positive, 17% had a family history of Spondyloarthritis.  70% had SI involvement confirmed radiographically. The average time between baseline and follow up clinic visits was 4.6 ± 2.3 months.  Correlations between both the BASDAI and the BASFI and active joint counts were found to be high (r = 0.6) while correlations with sites of enthesitis were found to be moderate (r = 0.3 – 0.4).  Responsiveness was greatest in effect size for the BASDAI for detecting worsening arthritis (0.8) and improving enthesitis (0.7).  For the BASFI, effect size was large for detecting worsening arthritis (0.9) and was moderate for improving enthesitis (0.4).

Conclusion: Our study demonstrates that the BASDAI and the BASFI show adequate construct validity and responsiveness and may be used in the evaluation of disease activity and functional impairment in children with JSpA.  Correlations were higher for both measures in arthritis than in enthesitis, and sensitivity to changes over time showed the largest effect sizes for detecting worsening arthritis.  For enthesitis, the BASDAI showed a larger effect size for detecting improving enthesitis than the BASFI.  The results of this study illustrate that these two instruments validated in adults may become an objective addition to developing Paediatric JSpA core sets.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/validation-of-basdai-and-basfi-in-children-with-spondyloarthritis/