Elsevier

Journal of Clinical Densitometry

Volume 15, Issue 3, July–September 2012, Pages 260-266
Journal of Clinical Densitometry

Original Article
Identification of Rheumatoid Arthritis Patients With Vertebral Fractures Using Bone Mineral Density and Trabecular Bone Score

https://doi.org/10.1016/j.jocd.2012.01.007Get rights and content

Abstract

The aim of this study was to test bone mineral density (BMD), trabecular bone score (TBS), and their combination, for detection of rheumatoid arthritis (RA) patients with vertebral fractures (VFs). One hundred eighty-five women aged 56.0 ± 13.5 yr, with RA since 15.5 ± 9.9 yr were studied. Lumbar spine, total hip, and femoral neck BMD were assessed by dual-energy X-ray absorptiometry (DXA). TBS was calculated from anteroposterior image of lumbar spine BMD. VFs from T4 to L4 were evaluated using Vertebral Fracture Assessment software on DXA device. The proportions of patients with VF and T-scores ≤−2.5 were only 24.2%, 21.2%, and 33.3% at lumbar spine, total hip, and femoral neck, respectively. T-scores were significantly lower in patients with VF than in patients without VF, the largest difference being observed at femoral neck (p = 0.0001). TBS was significantly lower in patients with VF vs without VF (p = 0.0001). The areas under the curves were 0.621, 0.704, 0.703, 0.719, and 0.727 for lumbar spine BMD, TBS, lumbar spine BMD + TBS, total hip BMD, and femoral neck BMD, respectively. The threshold of 1.173 for TBS had the best sensitivity (63%) and specificity (74%). TBS measured at the lumbar spine has a better discrimination value than lumbar spine BMD, and similar to femoral neck BMD, for prediction of presence of VF in patients with RA. In RA subjects with osteopenia, the proportion of patients with VF was higher in the lowest tertile of TBS when compared with the highest tertile. In this population, at low risk according to BMD, TBS could help to detect patients with VF.

Introduction

Bone involvement is the main extra articular complication of rheumatoid arthritis (RA). Patients with RA have a greater risk of osteoporosis and fracture than the general population (1). The most important factor involved in the pathogenesis of osteoporosis is the inflammation because of disease activity through the effect of inflammatory cytokines. Other well-known risk factors are glucocorticoids (GCs) use, menopausal status, low body mass index (BMI, kg/m2), and reduced physical activity (1). Population-based controlled studies have shown that the relative risk of having at least 1 vertebral fracture (VF) is 1.7–2.3 2, 3, 4 and up to 6.2 (5) in RA patients. Consequences of VFs such as chronic back pain, thoracic kyphosis, functional impairment, and back-related disability, are added to the disability of the RA itself (1).

A low bone mineral density (BMD) is also a determinant of VF risk. Prevalence of osteoporosis in RA is 20–30% at the spine and 7–26% at the hip 6, 7, 8, 9, 10. However, there is a discrepancy between low BMD and fracture risk, and a number of fractures are observed in patients with T-scores, which are not in the osteoporotic range. T-scores in RA patients with VFs are between −1.2 and −2.7 at the spine 2, 11, and between −1.4 and −1.7 at total hip 2, 11, but the risk of VFs has been described to be higher in RA compared with patients with postmenopausal osteoporosis or controls 2, 4, 5, 11. This discrepancy may be related to alterations of bone, which are not captured by BMD measurements, that is, changes in bone quality. Such decreases in bone quality (including parameters of mineralization, bone matrix, microarchitecture) have been described to be related to both inflammation (1) and long-term GCs treatment 12, 13. A challenge in clinical practice is thus to have a tool able to detect patients with a risk of having fractures although their BMD is not in the osteoporotic range.

The trabecular bone score (TBS) is a texture parameter assessing the pixel gray-level variations in dual-energy X-ray absorptiometry (DXA) images. The method was initially based on micro-computed tomography (μCT, 3 dimensional [3D]) images, then adapted for 2-dimensional projections obtained by DXA. The method builds an experimental variogram from the gray-scale variations in pixels in multiple random directions, and TBS is the slope at the origin of this variogram (on a log-log representation). There is no direct relation of TBS with microarchitectural parameters, nor trabecular network. On trabecular bone specimens, TBS measured with an experimental tool is correlated with the main 3D microarchitectural parameters, measured by μCT 14, 15.

The software for TBS computation can be installed on DXA machines, and TBS is automatically calculated consecutively on BMD measurement. A low TBS value indicates few gray-level variations of large amplitude and is intuitively interpreted as a low quality of bone texture.

In postmenopausal women, TBS is lower in patients with osteoporotic fractures compared with BMD-matched women without fracture (16). In a retrospective analysis of the Manitoba Study, TBS predicts osteoporotic fractures independent of bone density (17).

The aim of this study was to test TBS, BMD, and their combination in the detection of RA patients with VF.

Section snippets

Study Subjects Selection

Participants were 185 women with RA who fulfilled the American College of Rheumatology criteria (18). They were consulting in the tertiary Department of Rheumatology of Cochin Hospital, Paris, France between February 2009 and July 2010 for a BMD measurement as part of the routine procedure in RA.

Clinical assessment included demographic data: age, height, weight, and BMI (kg/m2). Disease duration was defined as the time elapsed between the onset of first disease-related symptoms and enrollment.

Patients’ Characteristics

Between February 2009 and July 2010, 185 women with RA (mean age of 56.0 ± 13.5 yr) were included in the study. Their main characteristics are summarized in Table 1. Among them, 133 (71.9%) women were rheumatoid factor positive. The mean disease duration of RA was 15.5 ± 9.9 yr. In our population, 162 women (88.1%) were treated with DMARDs, 130 (70.3%) with biological agents, and 112 (60.5%) were currently treated with GCs at a mean daily dose of 6.4 ± 4.3 mg per day equivalent prednisone.

Thirty-three

Discussion

This study is the first assessing the value of TBS in patients with RA. A high proportion of these patients have VFs although their bone density is above the osteoporotic threshold, and a low TBS is associated with a higher risk of having such fractures.

Our results confirm that a generalized osteoporosis is observed in RA: 30% of our patients with a mean age of 56 yr had a T-score below −2.5, and 18% had at least 1 VF. Both hip BMD and lumbar spine TBS were correlated to HAQ, which assesses the

References (22)

  • M.C. Lodder et al.

    Radiographic damage associated with low bone mineral density and vertebral deformities in rheumatoid arthritis: the Oslo-Truro-Amsterdam (OSTRA) collaborative study

    Arthritis Rheum

    (2003)
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