Differences in spinal mobility measures in relation to disease duration and between subgroups with axial spondylarthritis

• Background/Purpose: Spinal mobility is a core domain for research and clinical practice in Ankylosing Spondylitis (AS) but less studied in undifferentiated SpA (USpA). Our objective was to study the change of commonly used spinal mobility measures stratified on disease duration in patients with AS and differences in these measures in AS vs. USpA.Methods: Patients with AS or USpA were identified from a cohort attending a specialist clinic. A cross sectional studie were the first measures of spinal mobility for each patient recorded during 1999 to 2012 were analyzed. Disease duration was split into tertiles, (<17 years (G1), 18-30 years (G2) and >31 years (G3)). Differences between AS G1/G2/G3 were calculated with Kruskal-Wallis. Differences between AS and USpA were controlled for sex and disease duration (ANCOVA).Results: 126 patients with AS vs. 57 with USpA were included in the study, mean (SD) age 48.4 (13.7) vs. 41.6 (11.4) years and 23% vs. 46% were women. In AS, lumbar, and thoracic measures, vital capacity and the BASMI composite score were the first measures to deteriorate in relation to disease duration (G1 vs. G2, p<0.035). Late in the disease all measures had deteriorated (G1 vs. G3, p<0.036). Patients with USpA presented better scores in lumbar, hip and thoracic spinal measures (p<0.05), data controlled for sex and disease duration. In early disease (<17 years) also cervical measures (p<0.05) were less affected compared to patients with AS.Conclusion: The first measures to significantly change during the disease course in AS were the lumbar and thoracic mobility measures and the BASMI score. As expected, patients with USpA were less affected in mobility than patients with AS.

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