Background The zygapophyseal (ZA) joints of the cervical spine are frequently affected in ankylosing spondylitis (AS). Longitudinal data about the development of damage in the ZA joints is limited.
Objectives To investigate the prevalence of radiographic ZA joint involvement in the cervical spine and to explore the associations with patient characteristics, clinical assessments, and cervical radiographic damage according to the modified Stoke AS Spine Score (mSASSS) in AS patients with active disease. Furthermore, to investigate the incidence of ZA joint involvement during 4 years of TNF-α blocking therapy.
Methods This study included consecutive AS patients with active disease from the Groningen Leeuwarden AS (GLAS) cohort with available lateral cervical radiographs at baseline and after 4 years of follow-up. Patients fulfilled the modified New York criteria for AS and the ASAS criteria to start TNF-α blocking therapy. ZA joints of C2-C3 up to C6-C7 were scored by two trained and independent readers blinded to patient characteristics and time sequence according to the method of de Vlam et al. (0=normal, 1=joint space narrowing or erosion, 2=partial blurring or ankylosis, 3=complete blurring or ankylosis). ZA joint involvement was present if at least one ZA joint had a score ≥1. The mSASSS was scored to assess radiographic damage of the vertebral bodies and the presence of bridging syndesmophytes. Independent samples T-test, Mann-Whitney U test, and Chi-square test were used to evaluate the relationship with patient characteristics, clinical assessments, mSASSS, and bridging syndesmophytes.
Results 108 patients were included with a mean age of 43±11 years, median symptom duration of 17 (range 1-50) years, 76% was male, 84% was HLA-B27 positive, mean BASDAI was 5.9±1.7, and mean ASDAS was 3.8±0.8. At baseline, 45% of the patients had ZA joint involvement with on average 3 ZA joints involved. Complete ankylosis of at least one ZA joint or of the entire cervical spine was present in 19% and 2% of the patients, respectively. Ankylosis occurred most frequently at C2-C3 level. Patients with ZA joint involvement were significantly older (46 vs. 40 year), had longer symptom duration (22 vs. 15 years), larger occiput-to-wall distance (9 vs. 2 cm), higher mSASSS (median 16 vs. 4), and more often bridging syndesmophytes (57% vs. 22%). After 4 years of follow-up, 8% of the patients had developed new ZA joint involvement. Furthermore, 18% of the patients who already had ZA joint involvement developed damage in other ZA joints.
Conclusions In this cohort of AS patients with active disease, radiographic ZA joint involvement was very common and associated with assessments of more longstanding disease. The incidence of ZA joint involvement was low during 4 years of TNF-α blocking therapy.
Acknowledgements The GLAS cohort was supported by an unrestricted grant from Pfizer. Pfizer had no role in the design, conduct, interpretation, or publication of this study.
Disclosure of Interest F. Maas: None declared, S. Arends Grant/research support from: Abbott, Pfizer, Wyeth, E. van der Veer: None declared, F. Wink: None declared, M. Efde: None declared, H. Bootsma: None declared, R. Chaudhry: None declared, E. Brouwer Grant/research support from: Abbott, Pfizer, Wyeth, A. Spoorenberg Grant/research support from: Abbott, Pfizer, Wyeth, Consultant for: Abbvie, Pfizer, UCB
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