Objective: There is a lack of knowledge on factors that reliably can predict radiological changes in patients with AS. We have investigated whether urinary C-terminal cross-linking telopeptide of type I (CTX-I) and type II (CTX-II) collagen, as specific biochemical markers of bone and cartilage degradation, respectively, are associated with radiological damage and progression, and with BMD in patients with AS.
Methods: Eighty-three patients with AS [mean (s.d.) age: 50.4 (12) yrs, 65% male, mean (s.d.) disease duration after diagnosis: 16.7 (10) yrs] who participate in an ongoing cohort study of patients with AS [Outcome in AS International Study (OASIS) cohort] were assessed for urinary CTX-I and -II. Results of both biochemical markers were compared with baseline scores for radiological damage (modified modified Stoke Ankylosing Spondylitis Spine Score, primarily reflecting syndesmophyte-formation and -growth), and with scores for radiological progression after 2 yrs follow-up. Markers were also associated with disease activity parameters and BMD.
Results: Mean duration of complaints was 28.6 yrs. At that time, 54% of patients had signs of radiological damage, and 35% of them showed radiological progression after 2 yrs. Baseline radiological damage (rho = 0.24; P <or= 0.05) correlated with CTX-II, but not with CTX-I. CTX-II correlated with serological markers of inflammation (ESR rho = 0.29 and CRP rho = 0.30; P <or= 0.01), but not with baseline BASDAI or BMD. There was a negative correlation between CTX-I and BMD of the trochanter (rho = -0.31; P <or= 0.01) In multivariate analyses, CTX-II significantly and independently contributed to explaining variation in radiological damage (standardized beta = 0.27; P = 0.03) and progression (standardized beta = 0.27; P = 0.05).
Conclusion: In AS, cartilage degradation plays a role in explaining radiological-damage and -progression in the spine.