Intra-rater reliability of the bath ankylosing spondylitis disease activity index (BASDAI) and the bath ankylosing spondylitis functional index (BASFI) in children with spondyloarthritis

Purpose Juvenile spondyloarthritis (JSpA), referred to as enthesitisrelated arthritis (ERA) sub-type under the International League of Associations for Rheumatology (ILAR) classification of juvenile idiopathic arthritis (JIA), is characterized by inflammation in the joints and entheses. Axial involvement is uncommon at presentation but may develop in the second decade of life. Several instruments assessing disease activity in ankylosing spondylitis have been validated including the BASDAI and BASFI. At this time, there are no disease activity scores for JSpA or ERA. The objective of this study is to measure the intra-rater reliability of the BASDAI and the BASFI in JSpA/ERA.