Assessing cross-sectional, group-level spinal mobility measures in individuals with early axial spondyloarthritis (axSpA) was helpful when discriminating disease severity and activity, according to a study recently published in Rheumatology.
This study included data on individuals from the SPACE (n=148) and DESIR (n=328) cohorts. The SPACE study is an ongoing observational study in Europe with 2.6 years of follow-up available. The study involves individuals with chronic back pain (between 3 months and 2 years of duration) with an onset before the age of 45 years. DESIR is a French study with 5 years of data available, including those with early back pain indicative of axSpA. Spinal mobility measures were compared with threshold values from healthy individuals, with longitudinal analysis performed for individuals and cross-sectional analysis conducted at the group level. To assess the potential effect of disease and patient characteristics on spinal mobility, subgroup analyses were performed. Intraclass correlation coefficients with the smallest detectable changes were used to examine reliability.
The most impaired spinal mobility measures among the 2 cohorts were the modified Schober test (DESIR, 52%; SPACE, 20%) and lateral spine flexion (DESIR, 44%; SPACE, 41%). The combination of these 2 measures resulted in an 84% impairment in the DESIR cohort and a 74% impairment in the SPACE cohort for at least 1 spinal mobility measure.
Discrimination between subgroups was best accomplished using Bath AS Metrology Index and lateral spinal flexion. These revealed greater impairment, disease activity, and baseline syndesmophyte presence among those who received biologic treatment. Spinal mobility measures within individuals fluctuated over time. This variation persisted even when individuals with low disease activity were isolated for analysis. Spinal mobility measures received reliability scores ranging from fair to good (inter-reader intraclass correlation coefficients [ICC], 0.55-0.84; intra-reader ICC, 0.49-0.72).
Limitations to this study include certain assumptions that were deemed necessary in the course of spinal mobility measures. These assumptions were due to data-collection errors and other factors.
The study researchers concluded that “despite the fact that the assessment of spinal mobility over time appears to have several challenges, it seems that the limitations of the [spinal mobility measures] use are mainly at the individual patient level and in longitudinal assessments. The assessment of spinal mobility is particularly informative at the group level and cross-sectionally, enabling discrimination of patients with worse disease activity and severity.”
Marques ML, Ramiro S, Goupille P, Dougados M, van Gaalen F, van der Heijde D. Measuring spinal mobility in early axial spondyloarthritis: does it matter? [published March 16, 2019]. Rheumatology. doi:10.1093/rheumatology/kez026