Assessment of Bone Density in axSpA Benefits From Inclusion of Lateral DXA

Lateral dual-energy x-ray absorptiometry (DXA) is unaffected by spinal osteoproliferation in axial spondyloarthritis (axSpA) and should be included in bone mineral density (BMD) assessments of these patients, according to study results published in the International Journal of Rheumatic Diseases.

In patients with axSpA, osteoproliferation in the spine may lead to overestimation of DXA-measured BMD, warranting a need for better techniques to assess low BMD in this population. To determine the utility of incorporating lateral DXA in bone health assessments of patients with axSpA, researchers conducted an observational cross-sectional twin-center study to compare both lateral and conventional DXA projections in lumbar spine BMD assessments in this patient population, determine which variables might affect the accuracy of conventional DXA, and assess whether lateral DXA incorporation into bone health assessment affects the prevalence of low BMD.

Patients with axSpA were consecutively enrolled between April 2017 and January 2018. Demographic and disease-related data, including symptom duration, extra-articular manifestations, and osteoporosis history, were collected, and physical examinations and laboratory evaluations were conducted for all participants. A Hologic Horizon^® DXA scanner was used to measure BMD.

In total, 110 patients were enrolled and 100 with paired anteroposterior and lateral DXA of the lumbar spine were included (78% men; 98% white; mean age, 51.6±11.6 years; median disease duration, 23.6 years); a total of 7 participants reported a prior diagnosis of osteoporosis, 33 had ≥1 osteoporosis risk factor, and 5 had a history of either current or past definitive osteoporosis treatment.

Investigators found that spine BMD measured using anteroposterior (conventional) projection positively correlated with age, modified Stoke Ankylosing Spondylitis Spine Score (mSASSS), and Bath Ankylosing Spondylitis Metrology Index (BASMI). Conversely, spine BMD measured using lateral projection demonstrated no correlation with either mSASSS or BASMI and a nonsignificant inverse correlation with age. Similar patterns were noted with hip BMD.

Lumbar spine BMD measured with anteroposterior projection was significantly higher than BMD measured with lateral projection (mean difference, 0.34 g/cm²; 95% CI, 0.30-0.37). This difference correlated with age, mSASSS, BASMI, body mass index (BMI), and Bath Ankylosing Spondylitis Functional Index, indicating that older patients with more severe disease might experience a bigger difference between BMD measurements in these projections.

After controlling for biologic exposure and sex and correcting for multicollinearity, the R² of the final model for the difference between anteroposterior vs lateral BMD measurements was 0.4. Researchers found that disease duration, BMI, and mSASSS remained independently associated with differences between anteroposterior and lateral spine BMD.

Investigators identified 57 patients who fulfilled the criteria for BMD classification using T-scores. Within this cohort, 16% had low spine BMD measured using anteroposterior DXA compared with 47% when measured using lateral DXA (Chi-square, 7.4; odds ratio, 12.2; 95% CI, 1.4-106).

When anteroposterior spine and hip BMD were combined to assess for overall low BMD, 35% of patients had low BMD at a minimum of 1 site. When lateral spine and hip BMD were combined, 56% of patients had low BMD, which researchers noted was a statistically significant difference.

Study limitations included an inability to determine causality given the cross-sectional design of the study, a nearly exclusively white patient population, and an inability to draw conclusions related to the association between BMD and vertebral fractures.

“Including lateral DXA in the bone health assessment significantly increased the prevalence of low BMD in this [patient] population,” the researchers concluded. “Lateral DXA should be routinely added to the BMD assessment of individuals with axSpA.”

Disclosure: This clinical trial was supported by AbbVie. Please see the original reference for a full list of authors’ disclosures.

Reference

Fitzgerald G, Anachebe T, McCarroll K, O’Shea F. Measuring bone density in axial spondyloarthropathy: time to turn things on their side? [published online January 7, 2020]. Int J Rheum Dis. doi:10.1111/1756-185X.13765