Prevalence and risk factors of osteoporosis and vertebral fractures in patients with ankylosing spondylitis

Abstract

Ankylosing spondylitis (AS) is characterized by inflammation of the entheses and paravertebral structures, leading in time to bone formation at those sites. As well, vertebral bone loss is also a recognized feature of ASObjective: To calculate the prevalence and risk factors of osteoporosis and vertebral fractures in patients with AS.Methods: Eighty patients with AS were enrolled in the study. Clinical, biological and radiological status was assessed by the Bath AS Disease Activity Index (BASDAI), Bath AS Functional Index (BASFI), ESR and C-reactive protein (CRP), Bath AS Radiology Index (BASRI) and modified stoke AS spine score (mSASSS). BMD of the hip and spine was measured and vertebral fractures were defined using a combination of Genant semiquantitative (SQ) approach and morphometry by VFA (fracture vertebral assessment).Results: The years±11.8. The mean BMI was 22.8 kg/m2±4.1 and the mean disease duration was 10.8 years±6.6. Prevalence of osteoporosis was 25%. 18.8% of patients had a vertebral fracture (grades 2 and 3). Factors associated with osteoporosis were low weight and BMI and longer disease duration, higher ESR, CRP, BASFI and BASDAI. Vertebral fractures were associated with advanced age, longer disease duration, higher BASFI, BASRI and mSASSS and reduced BMD and T-score at the hip site, presence of osteoporosis at any site. Multiple logistic regression analysis (Table 4) revealed that parameters significantly associated with osteoporosis were BASDAI (OR=1.05, 95% confidence interval [CI]: 1.03–1.09); disease duration (OR=1.13, 95%CI: 1.03–1.25); and BMI (OR=0.82, 95%CI: 0.69–0.93). The presence of VFs (grades 2 and 3) were independently associated with disease duration (OR=1.50, 95%CI: 1.07–2.10); and mSASSS (OR=1.17, 95%CI: 1.05–1.30).Conclusion: Osteoporosis is common in patients with AS and seems to be related to disease activity while vertebral fractures appear to be related to the duration and structural severity of the disease rather than BMD.