Background/Purpose: In the diagnostic work-up of spondyloarthritis (SpA), imaging of the sacroiliac joints by MRI (MRI-SIJ) is an important step. One study showed that in HLA-B27+ patients and male patients it might be useful to repeat an MRI-SIJ after one or two years¹. It is not known if repeating an MRI-SIJ after a shorter period than 1 year is useful. Therefore, we investigated whether it is useful to repeat an MRI-SIJ after 3 months in the diagnostic process for SpA.

Methods: Patients with chronic back pain (n=157) (≥3 months, but ≤2 years, onset <45 years) included in the SPondyloArthritis Caught Early (SPACE)-cohort in the Leiden University Medical Center (LUMC) underwent an MRI-SIJ during baseline visit. All patients with SpA and possible SpA are included for follow-up (n=90) and received a second MRI-SIJ during a follow-up visit after 3 months. All MRI-SIJs of both time points were scored by 3 independent readers ‘positive' or ‘negative' according to the ASAS definition², blinded for the time-sequence. If 2/3 reads were positive, the MRI-SIJ was marked as positive.

Univariate and multivariate regression analyses were performed to investigate which variables (IBP, elevated CRP, MRI-SIJ status at baseline, gender, HLA-B27 status and age at onset) could predict a positive MRI-SIJ at 3 months.

Results: Only patients with complete MRI-SIJ data are included in this analysis (n=90). In the univariate analysis, MRI-SIJ positivity at baseline was the strongest predictor of a positive MRI-SIJ over time (OR 51.0, 95% CI 12.2-212.8, p<0.001). Regardless MRI-SIJ status, gender and HLA-B27-status (OR 7.7, 95% CI 2.6-23.1, p<0.001 and OR 2.6, 95% CI 0.9-7.0, p=0.07, respectively) are strong predictors of a positive MRI-SIJ over time. The latter 2 variables were used in a multivariate model. Groups were made based on this model (table). In the majority of the patients (90%), MRI-SIJ status, either positive (n=15) or negative (n=66), did not change over time. Of the patients with a negative MRI-SIJ at baseline (n=71), 5 (7%) developed a positive MRI-SIJ after 3 months, and in 4/19 (21.1%) lesions on MRI-SIJ disappeared over time. Two out of 5 patients in whom MRI-SIJ was positive for the first time at follow-up fulfilled the ASAS axial SpA criteria only at follow-up.

Conclusion: We confirmed that a positive MRI-SIJ at baseline is a very strong predictor for a positive MRI-SIJ after 3 months. In patients with a negative MRI-SIJ at baseline, male gender and HLA-B27+ are predictive for a later positive MRI-SIJ.

In this group of patients with short symptom duration, variation in MRI-SIJ positivity occurred in 10% of the patients over a very short period of only 3 months. A positive change of MRI-SIJ has led to a different classification in 2 patients (2.2%). More data are needed to decide if it is necessary to repeat MRI-SIJ, and if so, with what time interval.

References:

¹Van Onna M et al. ARD 2011

²Rudwaleit M et al. ARD 2009