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Low bone mineral density is common in axial spondyloarthritis; more awareness required

EULAR 2018
Cohort study, axSpA
Osteoporosis is typically related with inflammatory arthritis (IA). Although the impact of osteoporosis is well outlined in the general population and some IA, such as RA, it is often ignored in axSpA, which is a form of IA centred on sacroiliac joints and the spine. This can be explained by the fact that axSpA predominantly affects men, in whom osteoporosis is often not considered. As a result, osteoporosis prevalence figures are unclear, and a wide variation exists in the literature.

Accurate epidemiology regarding bone mineral density (BMD) in axSpA is crucial to understanding the impact of low BMD in this cohort. Investigating the prevalence of low BMD in a well-characterised axSpA cohort and exploring relationships (e.g. demographic, disease-related, laboratory) between BMD and axSpA were therefore the objectives of a research by Fitzgerald et al.[3]

A detailed assessment was performed on axSpA patients, including demographics, clinical characteristics, and laboratory investigations. A total of 104 patients with axSpA were consecutively recruited: 77.9% of them was male, 98.1% was Caucasian, the mean age was 51 years, and disease duration 26 years. The mean ASDAS-CRP was 2.3, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) was 3.9, Bath Ankylosing Spondylitis Metrology Index (BASMI) was 4.3, and Bath Ankylosing Spondylitis Functional Index (BASFI) was 3.8, reflecting mild to moderate disease burden. In 42.3% of subjects, a history of fracture was present, with only 3 fragility fractures reported. Osteopenia was observed in 42.3%, and 16.3% had osteoporosis. Low BMD was most prevalent at the spine, with 44% of the cohort affected followed by the femoral neck (30.1%). Low BMD at the radius was uncommon (seen in <10%). Only 6.4% of the cohort had a prior diagnosis of osteoporosis, and only 39.4% had a previous dual-energy X-ray absorptiometry. Three vertebral fractures were detected, and all patients were unaware of these fractures prior to the study.

Factors that were significantly associated with bone loss at both the spine and the hip were female gender, higher BASFI, lower BMI, and lower urate levels. ASDAS-CRP and BASDAI had no impact on low BMD. Additionally, longer disease duration was associated with spine BMD loss. Non-obese patients were more likely to have low BMD at any site than obese patients (62.3% vs 40%, odds ratio 2.5, P=0.04). The use of biologics did not influence BMD.

These findings led to the conclusion that low BMD is common in this axSpA cohort, with over 50% of patients affected. Most cases of low BMD were undiagnosed prior to this study and less than half of the cohort had ever had a dual-energy X-ray absorptiometry, which suggests a continued low awareness of the risk of osteoporosis in a still male-dominated disease.[3]

  1. Fitzgerald G, et al. Abstract HU0255. EULAR 2018.

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