Disability outcomes in early-stage African American and White people with multiple sclerosis

Background: Factors driving differences in disease burden between African American and White people with multiple sclerosis (pwMS) remain unclear. Here, we explored whether differences in disability outcomes could be observed after controlling for major sociodemographic factors and comorbidities, and assessed the presence of a possible interaction between MS and race. Methods: In this cross-sectional study, 120 pwMS within 6 years from disease onset and 82 healthy controls between 18 and 70 years of age, self-identified as either African American or White, were prospectively enrolled. Inclusion criteria for pwMS were: diagnosis of MS according to the revised McDonald criteria, relapsing-remitting phenotype and Expanded Disability Status Scale (EDSS) < 6.5. Study outcomes included: (i) global disability (EDSS); (ii) quantitative mobility and leg function (Timed 25 Foot Walk Test-T25FWT); (iii) quantitative finger dexterity (9-Hole Peg Test-9HPT); (iv) cognitive efficiency and speed performance (Symbol Digit Modalities Test-SDMT). Differences in disability outcomes were assessed employing multivariable linear regression models. Based on their association with MS or disability, covariates included age, gender, race, years of education, total income, body mass index, comorbidities. The interaction between MS and race on disability outcomes was estimated via relative excess risk of interaction and attributable proportion. Results: Accounting for age, gender, total income, education, body mass index and comorbidities, African American pwMS showed significantly worse performances in manual dexterity and cognition than White pwMS (White pwMS coeff. 3.24, 95% CI 1.55, 4.92 vs African American pwMS coeff. 5.52, 95% CI 3.55, 7.48 and White pwMS coeff. -5.87, 95% CI -8.86, -2.87 vs African American pwMS coeff. -7.99, 95% CI -11.58,-4.38). MS and race independently contributed to the observed gradient in disability severity. Conclusions: Complex social disparities and systemic racism might contribute to clinical heterogeneity in MS.