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http://ard.bmj.com/content/70/11/1981.abstract?etoc

HLA-B27 and gender independently determine the likelihood of a positive MRI of the sacroiliac joints in patients with early inflammatory back pain: a 2-year MRI follow-up study
M van Onna, A G Jurik, D van der Heijde, A van Tubergen, L Heuft-Dorenbosch, R Landewé

Contributors All listed authors have made an substantial contribution to the design and/or analysis and interpretation of the data. Furthermore, it was revised critically by every author and the current version was approved by the listed authors. There is no one else who fulfils the above-named criteria but has not been included as an author.

Accepted 24 June 2011
Published Online First 22 August 2011
Abstract
Objectives To describe how inflammation on MRI of the sacroiliac joints in patients with recent-onset inflammatory back pain (IBP) evolves over time, and to study determinants of activity on MRI of the sacroiliac joint.

Methods A 2-year follow-up study with annual MRI of the sacroiliac joints was conducted in patients with IBP of less than 2 years' duration. Images were scored for bone marrow oedema on short τ inversion recovery and enhancement after administration of gadolinium on T1.

Results Of the 68 patients (38% male; mean age 34.9±10.3 years) enrolled, 44 had a negative baseline MRI. Of these 44 patients, 39 patients had at least one follow-up MRI of whom six patients (15%) developed activity on MRI during follow-up. 24 patients (35%) had an abnormal MRI at baseline. In 23 of these 24 patients follow-up MRI was available. The MRI became negative in seven of these 23 patients (30%) during follow-up. Human leucocyte antigen B27 (HLA-B27) positivity and male gender determined independently the likelihood of a positive MRI at any time point. In an HLA-B27-positive patient the likelihood of a positive MRI during follow-up is 88% if the baseline MRI is positive and 27% if the baseline MRI is negative. In an HLA-B27-negative patient with a negative MRI at baseline the likelihood of a positive MRI during follow-up is less than 5%.
Conclusions A positive MRI at baseline predicts a positive MRI during follow-up in HLA-B27-positive patients. A negative MRI at baseline in HLA-B27-negative patients strongly predicts a negative MRI during follow-up.