Objectives Radiographic sacroiliitis is prerequisite for the diagnosis of ankylosing spondylitis (AS). Because of the development of unequivocal sacroiliitis may take about a decade, the diagnosis of AS is frequently delayed in patients with inflammatory back pain (IBP). This study was aimed to evaluate the relationship between the baseline sacroiliac (SI) joint magnetic resonance imaging (MRI) findings and the development of radiographic sacroiliitis and to test its possible prognostic significance in spondyloarthritis (SpA) and AS in particular.
Methods Patients with MRI examinations of SI joints ordered between the dates of June 26, 2002 through Dec 12, 2009 by the Rheumatology Department were identified. Those who also had available pelvic X-rays after at least one year of MRI examination were included in the primary endpoint analysis. MRI scans were evaluated according to the ASAS/OMERACT definitions and scored by using the Leeds Scoring System. SI joints in plain radiographs were scored according to the modified New York criteria. All radiographs and MRI examinations were scored by one of the investigators. Nine-teen radiographs and 24 MRI examinations were rescored to calculate intra-class correlation coefficient (ICC) and Cohen’s kappa value, respectively. Medical records of the patients were reviewed to obtain potentially relevant demographic and clinical data.
Results Initial screening of the radiology database identified 1122 patients with sacroiliac MRI examination. Of these patients, 328 (253 female [77%], and the mean age; 45.2±12.9) were considered eligible for the analysis since they had follow-up X-Rays after a mean of 33±19 months. HLA-B27 was tested in 155 patients with 40 (25.8%) of them being found positive. The reliability for diagnosing bone marrow edema was good (κ=0.750) and ICC values for right SI joints and left SI joints were 0.786 and 0.862, respectively. On presentation 15 patients fulfilled the modified New York criteria for AS and they were excluded from further analysis. Baseline MRI revealed sacroiliitis in 120 patients, with 44 of them having moderateto severe bone marrow edema. During a mean of 36±18 months follow-up period, 23 patients (7%) developed unequivocal radiographic sacroiliitis according to the modified New York criteria. Of them, 19 (83%) had bone marrow edema at baseline MRI. The development of radiographic sacroiliitis was correlated with the presence of bone marrow edema (r=0.233, p<0.001), as well as with the presence of structural changes (r=0.179, p=0.019) on baseline MRI, also with the gender (r=0.192, p<0.001), and inflammatory back pain according to the Calin criteria (r=0.169, p=0.003). However in the regression model, the presence of bone marrow edema (p=0.001) and male sex (p=0.009) were the only predictors of the development of radiographic sacroiliitis.
Conclusions Our findings indicate that in patients with “early SpA” the presence of bone marrow edema on MRI and male sex may predict future development of full blown AS. Relatively low frequency of HLA-B27 in our study group may have precluded to show its role in the development of AS.
Disclosure of Interest None Declared