Early diagnosis of ankylosing spondylitis: assessment the criteria for axial spondyloarthritis, proposedby the International Working Group of the Assessment of SpondyloArthritis Society (ASAS)

Objective: To test the significance of new criteria for axial spondyloarthritis (axSPA) in the early stages of ankylosing spondylitis (AS) and spondyloarthropathies (SPA) and that of changed ASAS criteria for inflammatory back pain.
Subjects and methods. The study enrolled patients aged 16 to 49 years who were consecutive visitors to the Research Institute of Rheumatology, Russian Academy of Medical Sciences, in 2006-2008 for chronic (a history of at least 3 months, but not more than 3 years) low back (LB) and/or thoracic portion (TP) pains without significant X-ray signs of sacroiliitis. In addition of pelvis X-ray study, goal-seeking collection of history data, and examination, sacroiliac joint (SJ) magnetic resonance imaging (MRI) (1,5 Tesla, Magnetom Symphony (Siemens)) was performed and HLA-B27 and erythrocyte sedimentation rate were determined in all the patients. X-ray and MRI of vertebral portions with pains being observed were, if needed, carried out. The diagnosis of axSPA was established in the detection of inflammatory LB and/or TP pains that met the criteria described by A. Calin et al., in the presence of MRI signs of sacroiliitis and/or spondylitis with no evidence for another interpretation of back pain. Pelvis X-ray films were assessed by two rheumatologists; MRI scans were estimated by a rheumatologist and a radiodiagnostician. The MRI diagnosis of sacroiliitis was made if there was one T2-FS medullary edema (ME) area (on at least two consecutive slices) or two areas or more (on at least one slice) in the SJ subchondral or periarticular regions. The MRI diagnosis of spondylitis was established if there was one T2-FS ME area (on at least two consecutive slices) or more (on at least one slice) in the vertebral bodies or posterior vertebral structures. The ESSG criteria or the criteria proposed by B. Amor et al. were used for the diagnosis of undifferentiated SA. Results. Early axSPA was diagnosed in 39 patients (a study group). A control group consisted of other 39 patients with chronic LB and/or TP pain without MRI signs of sacroiliitis and spondylitis. The patients' median age in these groups was 25 and 23 years; the median duration of back pain was 12 and 20 months; HLA-B27 was detected in 94,9 and 43,6% of the patients, respectively. The sensitivity of the first variant of the ASAS criteria was 84,6% and its specificity was 100%. These of the second variant of the ASAS criteria were 94,9 and 84,7%, respectively. With the consecutive use of the first variant of the ASAS criteria for early SPA, then their second variant, their sensitivity was as high as 100%. LB pain only was observed in 76,9% of patients with axSPA, 20% of them having wandering pains in the buttocks. In the control patients, LB pain was also predominant (71,7%). The sensitivity and specificity of the criteria proposed by M. Rudwaleit et al. and the ASAS (J. Siper et al.) were 89,7 and 85,7%; 89,7 and 100%, respectively. There were no statistical differences in the sensitivity of individual criteria. The specificity of the ASAS criteria was significantly higher than that of the criteria described by A. Calin (p=0,0000; double Fisher's test). Conclusion. With the consecutive use of the first variant of the ASAS criteria for early SPA, then their second variant, their sensitivity was as high as 100%. It is more preferential to use the criteria described by М. Rudwaleit et al. or the 2009 new criteria by the ASAS working group. The valuable symptom of inflammatory pain is wandering buttock pain, the specificity of which in patients with early axSPA was 100%.

axial spondyloarthritis, inflammatory back pain, magnetic resonance imaging, sacroiliitis, spondylitis

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