Factors Associated with Osteoporosis in People with MS Undergoing Bone Density Screening

Background: People with MS (PwMS) reportedly have a higher risk of low bone mineral density (BMD), osteoporosis and fractures compared to healthy adults. However, population-based studies examining BMD and osteoporosis prevalence in PwMS are limited. 

Objectives: We aimed to (i) compare BMD and osteoporosis frequency between PwMS and non-MS controls who received BMD screening, and (ii) determine if MS is an independent predictor of low BMD and osteoporosis after accounting for age, sex, area of residence, disability, prior fracture, history of falls, presence of specific comorbidities, medication use, and continuity of ambulatory physician care.

Methods: Using the population-based databases held at Manitoba Population Health Research Data Repository, which includes all BMD test results for Manitoba, we identified PwMS with BMD screening (MS-cases, n=783).  We then matched 5 non-MS controls with BMD screening (n=3915) to each MS case by age, sex, and first BMD screening date. We compared the groups with respect to femoral neck BMD using linear regression, and likelihood of osteoporosis (defined as BMD T-score -2.5 or lower) using logistic regression. Potential interactions between having MS and other covariates were investigated.

Results: The average BMD T-score at the femoral neck among MS cases was -1.48±1.08 and -1.12±0.98 among controls. MS was independently associated with femoral neck BMD (β estimates: -0.24; 95% confidence interval [CI]: -0.32, -0.17; p<0.01). The unadjusted prevalence of osteoporosis among MS-cases was 17%, compared to 6.5% among controls. MS was independently associated with osteoporosis (adjusted odds ratio [aOR]: 2.41; 95%CI: 1.82, 3.19; p<0.01). Other factors significantly associated with osteoporosis included: age, sex, BMI, disability, long-time antispasmodic users, and chronic lung disease. The only significant interaction was for prior fracture (p=0.02), which was strongly associated with osteoporosis in PwMS (aOR: 2.70; 95%CI: 1.28, 5.70; p<0.01) but not in controls (aOR: 1.07; 95%CI: 0.62, 1.85; ns).

Conclusions: Within a population undergoing BMD screening, PwMS had lower BMD and a higher rate of osteoporosis compared to matched controls, even after multiple covariate adjustments. These findings suggest that MS be considered as a secondary cause of osteoporosis.