Bone edema on magnetic resonance imaging is highly associated with low bone mineral density in patients with ankylosing spondylitis

OBJECTIVE To determine bone mineral density (BMD) using the posteroanterior L2-L4 (PA) and lateral L3 (LAT-L3) projections of dual energy x-ray absorptiometry (DEXA) in patients with ankylosing spondylitis (AS), and to evaluate the relationship between BMD and the presence of syndesmophytes. METHODS Twenty men with AS were studied. BMD was measured by femoral neck DEXA, PA DEXA, and LAT-L3 DEXA scans. Radiographs of lumbar spine were evaluated to obtain a lumbar spine score (LSS) for the presence of syndesmophytes. Twenty-three age matched healthy men served as controls. RESULTS While there was no significant difference in BMD from PA DEXA results between AS patients and controls, BMD from the LAT-L3 DEXA was significantly reduced in AS patients (p = 0.009). LSS correlated significantly with BMD from PA DEXA (r = 0.55, p = 0.013), but not with BMD of LAT-L3 DEXA. CONCLUSION LAT-L3 DEXA was superior to PA DEXA in detecting a decrease of BMD in patients with AS. The presence of syndesmophytes had no distorting effect on BMD measured by LAT-L3 DEXA.