Background Ankylosing spondylitis (AS) is a chronic rheumatic disorder resulting in axial deformation due to (osteo)sclerosis and postinflammatory vertebral decalcification. Therefore measuring axial bone density is complicated in AS. Limited data are available on the potential role of quantitative ultrasound (QUS) for screening of osteo-porosis in a high-risk patient group with AS. We evaluated test characteristics of Sahara calcaneus QUS by comparison with data from dual-energy X-ray absorptiometry (DEXA) in AS.
Methods From July 1999 up to July 2000, 39 consecutive AS patients were recruited, after informed consent, at the Outpatient Department Rheumatology of Leeuwarden/Zwolle. All patients had Sahara calcaneus QUS (hologic) and DEXA (hologic/lunar) with an interval of less than 3 mos.
Results 12 female, 27 male AS patients, mean age 49 yr (SD:12 yr), mean SI score 3.3–3.3 (0–4) were assessed: AS duration > 10 yrs: n = 29, <9 yrs: n = 10. HLA B27 positivity in 88%. Mean (SD) bone density was 532 (114) in calcaneus using Sahara QUS, 838 (112) in femoral column using DEXA, and 615 (178) in Ward’s using DEXA. Pearson correlation of estimated calcaneal density using QUS – lumbar AP T score is 0.41 (p < 0.05), and QUS – Ward’s T score 0.36 (p < 0.05).
Conclusion In our study population pretest probability for axial/femoral osteopenia increases 18–19%; pretest probability for axial osteoporosis increases 30% using T <-1.0 in calcaneus QUS. Prior to applying QUS for screening of osteoporosis in high-risk populations as AS a further improvement of QUS is warranted.
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