Low bone mineral density and the presence of existing spinal syndesmophytes predict the formation of new spinal bony growths and radiographic progression in axial spondyloarthritis (axSpA) at 2 years, according to research conducted by Hyoung Rae Kim of the Catholic University of Korea, Seoul, South Korea, and colleagues.
The investigators noted that low bone mass in ankylosing spondyloarthritis (AS) had been linked in previous studies to spinal structural damage yet “despite the identification of this relationship, it is not yet known whether the presence of low bone mass can independently predict radiographic spinal progression in axSpA patients.”
In order to evaluate the association between low bone mass and the formation of new syndesmophytes and to investigate whether low bone mineral density (BMD) independently predicted radiographic progression in axSpA, the researchers enrolled 119 patients with definite axSpA into their study, published in Arthritis Research & Therapy.
They defined low BMD as z scores of less than or equal to –2.0 and spinal radiographic progression as worsening of the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) by 2 or more points over the 2-year follow-up period.
Overall, 34 (29%) of the patients had syndesmophytes at baseline, 90 (76%) had radiographic sacroiliitis fulfilling the modified New York criteria for the classification of AS, and 19 (16%) had low BMD.
At 2 years, new syndesmophytes had developed in 22 (21%) of the patients. New syndesmophyte formation occurred in 15% of patients without low BMD and in 37% of patients with low BMD (P = .047).
In the multivariable analysis, current smoking (odds ratio, 3.0; 95% confidence interval, 1.1-7.7), the presence of syndesmophytes (OR, 4.6; 95% CI, 1.8-11.9); and low BMD at baseline (OR, 3.6; 95% CI, 1.2-11.2) were independently associated with significant spinal progression, the investigators reported.
The presence of baseline syndesmophytes and low BMD at any site (OR, 5.5; 95% CI, 2.0-15.2; and OR, 3.6; 95% CI, 1.1-11.8, respectively) was identified by the investigators as significant predictors of new syndesmophytes.
“The presence of a syndesmophyte at baseline and low BMD were predictors of the formation of new syndesmophytes and significant mSASSS progression. … This study is the first to demonstrate that low BMD predicts radiographic progression in axSpA,” they concluded.
The investigators noted that a potential driving mechanism for the ankylosing process was bone loss resulting from chronic inflammation and the associated changes in bone microarchitecture.
“The inflammatory process induces bone loss, which affects the microarchitecture in the trabecular bone, thereby leading to instability. Reduced bone strength triggers a stabilizing anabolic effort that results in bone formation,” they wrote.
“Our results suggest that successful anti-inflammatory treatment reduces inflammation and allows the bone metabolism to normalize, thereby taking away the compensatory anabolic response that leads to new bone formation in the cortical bone of the spine,” they said.
They noted that their study was limited by its small sample and their findings needed confirmation in larger cohorts of axSpA patients.
SOURCE: Arthritis Res Ther. 2018 Oct 16. doi: 10.1186/s13075-018-1731-8.