As shown in Table 1, the study population recruited 137 ax-SpA patients (115 from Phramongkutklao Hospital and 22 from Khon Kaen University Hospital) and 137 matched healthy controls. Most participants were male (75.9%), and 34.3% of women were menopause. The mean (SD) of age and mean duration of disease were 42.8 (12.0) years and 86.8 (96.9) months, respectively. HLA-B27 was found in 88.3%, whereas the family history of ax-SpA was found in only 13.1%. Patients with ax-SpA had concomitant anterior uveitis and psoriasis (5.8% and 1.5%, respectively). In ax-SpA patients, alcohol consumption who used greater than or equal to 3 units/day was found in 19.7%, whereas patients with smoking including ex-smoker were found in 35.8%.
The mean LS-BMD was significantly higher in ax-SpA patients compared with the controls. In contrast, the mean FN-BMD was significantly lower in ax-SpA patients than in the controls. There was no significant difference in TH-BMD between the two groups. The mean TBS was significantly lower in patients with ax-SpA compared with controls. The prevalence of degraded bone/low TBS in the ax-SpA patients was also significantly higher than that in the controls (7.35% vs 1.46%, p=0.010). The prevalence of low BMD/osteoporosis at TH was significantly higher in ax-SpA patients than that in the controls, but it was not significantly different between ax-SpA patients and the controls at LS and FN (Table 1).
As depicted in Table 2, ax-SpA patients with degraded bone/low TBS group had higher CRP level, disease activity scores (including PGA, BASDAI, BASFI, BASMI, and ASDAS), and prevalence of grade 4 sacroiliitis and current NSAIDs use than those in normal and high TBS groups. In addition, ax-SpA patients with degraded bone/low TBS group had a significantly shorter disease duration when compared with other groups. We found that patients with ax-SpA who had never received anti-TNF or anti-OP medication had lower TBS than patients who had received those medications. (p=0.037 and p=0.028, respectively).Furthermore, ax-SpA patients with degrade bone/low TBS group had significantly lower BMD at LS, FN, and TH than those with intermediate/ normal TBS groups. The radiographic VFs were found in 10 patients (7.5%, 10/134). The prevalence of VFs was significantly higher in patients with degraded bone/low TBS group as compared with patients with intermediate and normal TBS groups (30.0% vs 6.67% vs 5.5%, p=0.019, respectively).
Factors associated with trabecular bone score
In the univariate linear regression, ex- or current smoker, alcohol intake ≥ 3 units/day, BMI, current NSAIDs use, all parameters of disease activity, presence of syndesmophyte, and grade 4 sacroiliitis were associated with low TBS. In multivariate linear regression analysis, TBS was negatively associated with female gender, ex- or current smoker, alcohol intake ≥ 3 units/day, ASDAS, and grade 4 sacroiliitis, whereas BMI was positively associated with TBS.
The univariate logistic regression model showed that higher disease severity measurement including PGA, ESR, hsCRP, BASDAI, BASMI, BASFI, ASDAS, grade 4 sacroiliitis and the presence of syndesmophyte, alcohol intake ≥ 3 units/day, shorter disease duration, and PPI uses were significantly associated with degraded bone/low TBS. The ASDAS and grade 4 sacroiliitis were respectively selected to represent current disease severity and damage in multivariate models. In multivariate logistic regression, ASDAS, and grade 4 sacroiliitis were independently associated with degraded bone/low TBS with the adjusted odds ratios (confidence interval: CI) of 5.228 (1.611-16.963) and 11.820 (1.211-115.412), respectively. Short disease duration was also found to be associated with degraded bone/low TBS; however, the association was modest with an adjusted odds ratio (CI) of 0.982 (0.966-0.998), (Table 3).
VFs were found in 10 patients in this study (7.5%). The prevalence of VFs was significantly higher in degraded bone/low TBS group than in intermediate and normal TBS groups (30.0% vs 6.67% vs 5.50%, p=0.019, respectively), (Figure 1). For identifying patients with VFs, the sensitivity (95%CI) and specificity (95%CI) of degraded bone/low TBS were 30% (6.67% to 65.25%) and 94.35% (88.71% to 97.70%), whereas the sensitivity (95%CI) and specificity (95%CI) of osteoporosis/low bone mass at LS-BMD and FN-BMD were 10.0% (0.25%-44.50%) and 94.4% (88.8%-97.72%) and 16.67% (0.42%-64.12%) and 92.56% (86.35%-96.54%), respectively.
Combining the results from TBS and BMD, ax-SpA patients who had both degraded bone/low TBS and osteoporosis/low bone mass at the femoral neck or total hip were at the highest risk of having VFs as compared to patients with normal TBS and FN-BMD group with the OR (95%CI) of 15.8 (0.88-285.48), p= 0.061 for both femoral and total hip site. In contrast, ax-SpA patients that had normal BMD and degraded bone/low TBS at the lumbar spine had increased risk of VFs as compared with those with normal BMD and normal TBS at the same site with the OR (95%CI) of 11.3 (1.58-81.23), p=0.016), (Figure 2).