OBJECTIVES: The aim was to investigate the reliability, validity, and sensitivity to change of a novel MRI scoring system in early peripheral SpA (pSpA).

METHODS: MRI of pelvis and lower extremities was performed before initiation of the TNF inhibitor golimumab in 56 patients and repeated in 46 patients who achieved sustained clinical remission after 24, 36 or 48 weeks. Three readers applied a semi-quantitative MRI scoring system for lower-extremity joint and entheseal inflammation. Four lesion types were assessed: entheseal osteitis, entheseal soft tissue inflammation, joint osteitis, and joint synovitis/effusion. MRI response was defined as a decrease in MRI lower-extremity inflammation index (sum of scores from 75 sites, each scored 0-3) above the smallest detectable change (SDC).

RESULTS: At follow-up, the MRI index decreased in 34 of 46 patients (74%), and fifteen (33%) patients achieved MRI response, i.e. a decrease above SDC of 2.8. When restricting the analysis to patients with clinical involvement of lower-extremity sites that were assessed by MRI, 13 of 28 (46%) achieved MRI response. Interreader reliability was very good with average-measure ICC of 0.92 (95% confidence interval: 0.85-0.95) for status scores and 0.89 (0.80-0.94) for change in scores. The MRI index correlated with other measures of disease activity, including C-reactive protein (Spearman's rho 0.41 (0.23-0.56)), swollen joint count of 6 joints (0.47 (0.27-0.63)), tender enthesis count of 14 entheses (0.32 (0.12-0.50)) and pain score (0.28 (0.08-0.46)), all p< 0.05.

CONCLUSION: The proposed MRI lower-extremity inflammation index demonstrated reliability, validity, and sensitivity to change in patients with early pSpA.

TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT01426815.