Incorporating assessment of the cervical facet joints in the modified Stoke ankylosing spondylitis spine score is of additional value in the evaluation of spinal radiographic outcome in ankylosing spondylitis.

BACKGROUND: To aim was to investigate the additional value of incorporating the de Vlam cervical facet joint score in the modified ankylosing spondylitis (AS) spine score (mSASSS) for the evaluation of spinal radiographic outcome in AS.

METHOD: Baseline and 4-year radiographs from 98 consecutive patients from the Groningen Leeuwarden AS (GLAS) cohort, who had AS treated with TNF-α inhibitors, were scored by two readers; the vertebral bodies were assessed according to the mSASSS (0-72) and cervical facet joints (C2-C7) were assessed according to the method of de Vlam (0-15). The combined AS spine score (CASSS) was calculated as the sum of both total scores (range 0-87) and compared with the original mSASSS according to three aspects of the Outcome Measures in Rheumatology Clinical Trials (OMERACT) filter: feasibility, discrimination, and truth.

RESULTS: Feasibility: the CASSS was calculated in 91% of the patients. No additional radiographs were necessary and the assessment took only a few extra minutes. Discrimination: both scoring methods had excellent inter-observer reliability (intra-class correlation coefficient (ICC) status scores >0.99, progression scores 0.92). Incorporating the cervical facet joints did not result in an increase in measurement error. The CASSS detected more patients with definite damage (61% vs. 57%) and definite progression (55% vs. 48%). Truth: higher CASSS scores at baseline and higher progression scores were seen in 41 (46%) and 22 (25%) patients, respectively. Cervical rotation correlated better with cervical CASSS than with cervical mSASSS (Spearman's rho = 0.68 vs. 0.59).

CONCLUSIONS: The CASSS is a relevant and easy modification of the mSASSS. It captures more patients with AS who have spinal radiographic damage and progression, which is of great additional value in the evaluation of radiographic outcome in this heterogeneous and overall slowly progressing disease.