The precise anatomical location of pathology associated with inflammatory back pain (IBP) in early spondyloarthropathy (SpA) remains unclear.
To use MRI to study the sacroiliac joint (SIJ) and lumbar spine (LS) and explore the relationship between sites and extent of inflammation and HLA-B27 status over 12 months.
54 patients with IBP; median duration 24 weeks (54% HLA-B27 positive; median Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) 5.65) and 22 control subjects (11 with mechanical back pain; 11 volunteers) were recruited and 63% (n = 34) were reassessed at 1 year. Fat saturation and T1-weighted MRI was performed with images being scored for active bone marrow oedema (BMO) lesions representative of inflammation.
At baseline 46/54 (85%) patients had BMO (SIJs and LS) compared with 40% in the control group. The majority of affected patients had inflammation at the SIJ level (96% (n = 44); 23.5% (n = 12) LS) and 28.3% (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 1 year (p = 0.02). 90% of reattenders fulfilled European Spondyloarthropathy Study Group criteria; 73.5% showed MRI inflammation despite clinical improvement (median BASDAI 5.65 to 3.05; p<0.009).
LS and SIJ involvement may occur simultaneously in very early SpA and may be differentiated from non-inflammatory back pain by the severity of MRI lesions. HLA-B27 is associated with both the severity of osteitis and its persistence.