Abstract
BackgroundStudies have shown increased prevalence of osteoporosis and increased risk for vertebral fractures in patients with ankylosing spondylitis (AS). Measurements of bone mineral density (BMD) in the lumbar spine anterior-posterior (AP) projection may be difficult to interpret due to the ligamentous calcifications, and the lateral projection might be a better measuring site. Our objectives were to investigate BMD changes after 5 years at different measuring sites in patients with AS and to evaluate disease-related variables and medications as predictors for BMD changes.MethodsIn a longitudinal study, BMD in Swedish AS patients, 50 ± 13 years old, was measured with dual-energy x-ray absorptiometry (DXA) at the hip, the lumbar spine AP and lateral projections, and the total radius at baseline and after 5 years. Patients were assessed with questionnaires, blood samples, and spinal radiographs for grading of AS-related alterations in the spine with the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) and assessment of vertebral fractures by the Genant score. Multiple linear regression analyses were used to investigate predictors for BMD changes.ResultsOf 204 patients included at baseline, 168 (82%) were re-examined after 5 years (92 men and 76 women). BMD decreased significantly at the femoral neck and radius and increased significantly at the lumbar spine, both for AP and lateral projections. Mean C-reactive protein during follow-up predicted a decrease in the femoral neck BMD (change in %, β = –0.15, p = 0.046). Use of bisphosphonates predicted an increase in BMD at all measuring sites (p < 0.001 to 0.013), except for the total radius. Use of tumor necrosis factor inhibitors (TNFi) predicted an increase in AP spinal BMD (β = 3.15, p = 0.012).ConclusionThe current study (which has a long follow-up, many measuring sites, and is the first to longitudinally assess the lateral projection of the spine in AS patients) surprisingly showed that lateral projection spinal BMD increased. This study suggests that the best site to assess bone loss in AS patients is the femoral neck and that inflammation has an adverse effect, and the use of bisphosphonates and TNFi has a positive effect, on BMD in AS patients.
Highlights
Studies have shown increased prevalence of osteoporosis and increased risk for vertebral fractures in patients with ankylosing spondylitis (AS)
The Ankylosing Spondylitis Disease Activity Score based on C-reactive protein (ASDAS-CRP) was calculated [21, 22]
Values are mean ± standard deviation (SD) or numbers of patients (%) ASDAS-CRP Ankylosing Spondylitis Disease Activity Score based on C-reactive protein, BASDAI Bath Ankylosing Spondylitis Disease Activity Index, BASFI Bath Ankylosing Spondylitis Functional Index, BASMI Bath Ankylosing Spondylitis Metrology Index, CRP C-reactive protein, Dual-energy x-ray absorptiometry (DXA) dual-energy x-ray absorptiometry, ESR erythrocyte sedimentation rate, GC glucocorticoid, MHT menopausal hormone therapy, modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) modified Stoke Ankylosing Spondylitis Spine Score, NSAID nonsteroidal anti-inflammatory drug, tumor necrosis factor inhibitors (TNFi) tumor necrosis factor inhibitor
Summary
Studies have shown increased prevalence of osteoporosis and increased risk for vertebral fractures in patients with ankylosing spondylitis (AS). Measurements of bone mineral density (BMD) in the lumbar spine anterior-posterior (AP) projection may be difficult to interpret due to the ligamentous calcifications, and the lateral projection might be a better measuring site. Dual-energy x-ray absorptiometry (DXA) is the routine method for assessing BMD [6]; measurements at the anterior-posterior (AP) projection of the spine in AS patients may be difficult to interpret due to ligamentous calcifications superimposed on the vertebrae or to sclerosis of the vertebral endplates [1, 7]. In two studies on older men the lateral projection showed decreasing BMD over time whereas AP BMD increased [14, 15]
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