Prevalence and risk factors of low bone mineral density in juvenile onset ankylosing spondylitis.

The objective of this study is to assess the prevalence and risk in patients with juvenile onset ankylosing spondylitis (JoAS) complicated with low bone mineral density (BMD). A total of 112 children and adolescents with JoAS were enrolled in the study. Bone mass was measured from the lumbar spine and the left proximal femur using dual-energy X-ray absorptiometry. According to the 2007 International Society of Clinical Densitometry definitions, a Z score of less than -2 was termed as "low BMD." Stepwise regression analysis was used to investigate associations between low BMD and disease-related factors including gender, age, weight, height, body mass index, disease duration, HLA-B27 antigen, grades of sacroiliitis, Bath AS Disease Activity Index (BASDAI), Bath AS Functional Index (BASFI), patient global assessment (PGA), spine pain, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). Low BMD was found in 18 (16.1 %) cases in at least one of the two measured regions. Lumbar spine BMD had negative correlations with BASDAI, BASFI, spine pain, ESR, and CRP (P < 0.05). Hip BMD significantly negatively correlated with BASDAI and PGA (P < 0.05). In conclusion, patients with JoAS are likely to develop low BMD, which may be related to high disease activity.