Comparison of three methods for calculating the Bath Ankylosing Spondylitis Metrology Index in a randomized placebo-controlled study

Objective To compare 3 methods for calculating the Bath Ankylosing Spondylitis Metrology Index (BASMI) score using patients who participated in the GO-RAISE study. Methods Patients with active ankylosing spondylitis (AS) were randomly assigned in a 1:1.8:1.8 ratio to receive subcutaneous injections of placebo, golimumab 50 mg, or golimumab 100 mg every 4 weeks. Lumbar flexion, tragus-to-wall distance, lumbar side flexion, intermalleolar distance, and cervical rotation angle measurements at baseline, week 14, and week 24 were used to calculate the BASMI 2-step (BASMI2), 10-step (BASMI10), and linear (BASMIlin) scores. Results BASMI2 scores were generally lower than BASMI10 and BASMIlin scores, which were nearly identical. Median changes from baseline to week 14 in the combined golimumab group were similar to those in the placebo group when using the BASMI2 calculation method (0.00 versus 0.00; P = 0.288). The combined golimumab group showed significantly greater improvement from baseline to week 14 than the placebo group when using the BASMI10 (-0.20 versus 0.00; P = 0.018) and BASMIlin (-0.31 versus -0.07; P = 0.015) calculation methods, with the latter showing the greatest difference between golimumab and placebo. Guyatt's effect size was better for the BASMIlin and the BASMI10 versus the BASMI2 in the combined golimumab group at week 14 (0.58 and 0.53 versus 0.42, respectively) and week 24 (0.76 and 0.69 versus 0.61, respectively), despite the relatively short period to assess changes in spinal mobility. Conclusion The BASMIlin method was the most sensitive to changes in range of motion exhibited by patients with AS who received golimumab.