Objectives: The precise anatomical location of pathology associated with inflammatory back pain (IBP) in early SpA remains unclear. We used MRI to study the SIJ and lumbar spine (LS) and explored the relationship between sites and extent of inflammation and HLA-B27 status over 12 months.
Methods: 54 IBP patients; median duration 24 weeks (54% HLA-B27 positive; median BASDAI 5.65) and 22 control subjects (n=11 mechanical back pain; n= 11 volunteers) were recruited and 63% (n=34) were re-assessed at 1 year. Fat saturation and T1W MRI was performed with images being scored for active bone marrow oedema (BMO) lesions representative of inflammation.
Results: At baseline 85% of the patients had BMO (SIJs and LS) vs 40% in the control group. The majority of affected patients had inflammation at the SIJ level (95 % [n=44]; 23.5% [n=12] LS) and 28.2% (n=13) at both sites simultaneously. The SIJ activity score confirmed more severe inflammation (BMO grade 2 or 3: 52.2%) in the IBP group (controls= BMO grade 1: 100%; p<0.001). HLA-B27 was associated with both the severity (p=0.009) and number of baseline SIJ lesions (p=0.045) and with persistence (SIJ or LS) at one year (p=0.02). 90% of re-attenders fulfilled ESSG criteria; 73.5% showed MRI inflammation despite clinical improvement (median BASDAI 5.65 to 3.05; p<0.009).
Conclusion: LS and SIJ involvement may occur simultaneously in very early SpA and may be differentiated from non-inflammatory back pain on the severity of MRI lesions. HLA-B27 is associated with both the severity of osteitis and its persistence.