Bone mineral density in patients with early axial spondyloarthritis

Objective : to study bone mineral density (BMD) of the lumbar spine (LS) and femoral neck (FN) in patients with early axial spondyloarthritis (SpA) and to reveal its association with inflammatory disease activity. Subjects and methods . Seventy-three patients aged 18–45 years with inflammatory back pain lasting at least 3 months and not more than 5 years were examined. Axial SpA was diagnosed according to the 2009 ASAS criteria. BASDAI and ASDAS C-reactive protein (CRP) values were used to estimate disease activity; BASFI was employed to evaluate functional status. The examination encompassed determination of HLA-B27, X-ray of the pelvis and LS, magnetic resonance imaging (MRI) of sacroiliac joints, LS, and hip joints (in the presence of clinical signs of their injuries), densitometry of LS (L I-IV ) and FN. By taking into account the young age of patients, the Z-score was applied to measure BMD. The latter is considered lower if the Z-score is 1–2 standard deviations (SD) in at least one of the segments under study. Results . The median Z-score was -0.7 (-1.3; -0.3) SD for FN and 0.9 (-1.6; -0.5) SD for LS. Reduced BMD in at least one of the segments under study was detected in 13 (17.8%) patients: that in LS and FN in 11 (15.1%) and 5 (6.8%) patients, respectively. Lower BMD was observed in two segments in 3 (4.1%) patients. No association was found between lower BMD and age, gender, disease activity (BASDAI, ASDAS), and laboratory inflammatory markers (erythrocyte sedimentation rate (ESR) and CRP). A relationship was established between inflammatory changes according to the data of MRI of LS (MRI spondylitis) and reduced BMD in the same segment. MRI spondylitis was detected in 8 patients. Five and 3 patients with spondylitis of LS were found to have lower and normal BMD in this segment, respectively. Six out of 65 patients without MRI spondylitis in LS had its reduced BMD and the remaining (n=59) patients had its normal BMD (p=0.0014). Conclusion . There was an association between the active inflammatory changes as evidenced by LS MRI and the reduced BMD in this segment of the axial skeleton. Our data validate the hypothesis that in early axial SpA, bone is lost in the vertebral bodies due to local inflammation.