Prognostic value of the clinical and imaging arm of the ASAS criteria for progression of structural sacroiliac joint lesions.

ABSTRACT

OBJECTIVE: To investigate the prognostic value of the two arms of the Assessment of SpondyloArthritis international Society (ASAS) criteria regarding the progression of structural lesions in the sacroiliac joints (SIJ). METHODS: Information on baseline fulfilment of the ASAS criteria and baseline and follow-up magnetic resonance imaging of the SIJ in 603 patients aged 18-40 years, referred with low back pain to an outpatient spine were collected. MRI-positivity was defined as bone marrow oedema (BMO) in ≥2 consecutive slices or ≥2 lesions in 1 slice, as described in ASAS definition of sacroiliitis. RESULTS: Of 71 participants fulfilling the ASAS criteria at baseline, 66(93%) fulfilled the 'imaging arm' and 14(20%) the 'clinical arm'. The 'clinical arm' predicted progression of erosions with an odds ratio of 55 (compared with not fulfilling the ASAS criteria), while the 'imaging arm' predicted progression of erosions with an odds ratio of 8. Moreover, in 24% of patients in the 'imaging arm', all having BMO at the SIJ at baseline, the BMO disappeared without neither erosions nor ankylosis emerging. CONCLUSION: We found that the 'clinical arm' was a strong predictor for progression of sacroiliac joint erosion, while the 'imaging arm' had a more modest prognostic value for structural progression.