Relationship between spinal mobility and radiographic damage in ankylosing spondylitis and psoriatic spondylitis: a comparative analysis.

Objective: To correlate measures of spinal mobility used in the assessment of spondyloarthritis with radiographic severity, and to compare ankylosing spondylitis (AS) and psoriatic spondylitis (Ps-Sp) in this clinical-radiographic correlation.

Methods: As part of the International SPondyloarthritis Interobserver Reliability Exercise (INSPIRE) study, 20 spondyloarthropathy (SpA) experts met for an examination exercise assessing 19 patients with SpA -- 10 with Ps-Sp (9 men, mean age 52 yrs, mean disease duration 17 yrs) and 9 with AS (7 men, mean age 38 yrs, mean disease duration 16 yrs). Spearman correlation with bias correction was used to correlate median values of the spinal measurements obtained in the INSPIRE study with modified Stoke AS spinal score (mSASSS) and Bath AS Radiology Index-spine (BASRI-s) scores calculated by consensus of 2 assessors.

Results: The 2 radiographic measures performed comparably in relation to clinimetrics in the SpA group as a whole. There was very good correlation between mSASSS and the occiput-to-wall distance, tragus-to-wall distance, modified Schober, and lateral spinal flexion in the entire group (rs > 0.64, p < 0.05 for each measure). There was also good correlation between mSASSS and cervical rotation and chest expansion (rs = 0.58 and 0.54, p <0.05, respectively). The clinical-radiographic correlations were comparable in the AS and Ps-Sp, except for cervical rotation, which correlated better with mSASSS in Ps-Sp than in AS.

Conclusion: Our study documents the structure-function correlations in axial SpA and provides evidence supporting application of radiographic and clinical measures used in AS to studies of Ps-Sp.