Both structural damage and inflammation of the spine contribute to impairment of spinal mobility in patients with ankylosing spondylitis.
OBJECTIVE
To study the relationship between spinal mobility, radiographic damage of the spine and spinal inflammation as assessed by MRI in patients with ankylosing spondylitis (AS).


METHODS
In this subanalysis of the Ankylosing Spondylitis Study for the Evaluation of Recombinant Infliximab Therapy cohort, 214 patients, representing an 80% random sample, were investigated. Only baseline data were used. MRI inflammation was assessed by the AS spinal MRI activity (ASspiMRI-a) score, structural damage by the modified Stoke AS Spine Score (mSASSS) and spinal mobility by the linear definition of the Bath Ankylosing Spondylitis Metrology Index (BASMI). Univariate correlations were calculated on baseline values using Spearman rank correlation. Independent associations between the variables of interest were investigated by multivariate linear regression analysis. Associations with clinical disease activity, C-reactive protein, disease duration, age, gender, body mass index and HLA-B27 status were also investigated. Subanalyses were performed according to disease duration.


RESULTS
BASMI correlated moderately well with mSASSS (Spearman's rho=0.6) and weakly with ASspiMRI-a (rho=0.3). A best-fit model for BASMI included both mSASSS (regression coefficient (B)=0.865, p<0.001) and ASspiMRI-a (B=0.236, p=0.018). In patients with a disease duration < or = 3 years, B was greater for ASspiMRI-a than for mSASSS (0.595 vs 0.380), while in patients with a disease duration > 3 years B was greater for mSASSS than for ASspiMRI-a (0.924 vs 0.156).


CONCLUSIONS
Spinal mobility impairment in AS is independently determined both by irreversible spinal damage and by reversible spinal inflammation. Spinal mobility impairment is more influenced by spinal inflammation in early disease, and by structural damage in later disease.
Machado
Pedro
P
Rheumatology, Coimbra University Hospital, Coimbra, Portugal.
Landewé
Robert
R
Braun
Jürgen
J
Hermann
Kay-Geert A
KG
Baker
Daniel
D
van der Heijde
Désirée
D
D000328:Adult; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D018501:Antirheumatic Agents / Q000627:therapeutic use; D018450:Disease Progression; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D000069285:Infliximab; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D011859:Radiography; D016059:Range of Motion, Articular; D011994:Recombinant Proteins / Q000627:therapeutic use; D012720:Severity of Illness Index; D013131:Spine / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D013167:Spondylitis, Ankylosing / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*
D000911:Antibodies, Monoclonal; D018501:Antirheumatic Agents; D011994:Recombinant Proteins; D000069285:Infliximab