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Abstract
Objective: To determine whether the incidence of multiple sclerosis (MS) varies by race/ethnicity in a multiethnic, population-based cohort.
Methods: We conducted a retrospective cohort study of more than 9 million person-years of observation from the multiethnic, community-dwelling members of Kaiser Permanente Southern California health plan from January 1, 2008 to December 31, 2010. Incidence of MS and risk ratios comparing incidence rates between racial/ethnic groups were calculated using Poisson regression.
Results: We identified 496 patients newly diagnosed with MS who met McDonald criteria. The average age at diagnosis was 41.6 years (range 8.6–78.3 years) and 70.2% were women. The female preponderance was more pronounced among black (79.3%) than white, Hispanic, and Asian individuals with MS (67.8%, 68.1%, and 69.2%, respectively; p = 0.03). The incidence of MS was higher in blacks (10.2, 95% confidence interval [CI] 8.4–12.4; p < 0.0001) and lower in Hispanics (2.9, 95% CI 2.4–3.5; p < 0.0001) and Asians (1.4, 95% CI 0.7–2.4; p < 0.0001) than whites (6.9, 95% CI 6.1–7.8). Black women had a higher risk of MS (risk ratio 1.59, 95% CI 1.27–1.99; p = 0.0005) whereas black men had a similar risk of MS (risk ratio 1.04, 95% CI = 0.67–1.57) compared with whites.
Conclusions: Our findings do not support the widely accepted assertion that blacks have a lower risk of MS than whites. A possible explanation for our findings is that people with darker skin tones have lower vitamin D levels and thereby an increased risk of MS, but this would not explain why Hispanics and Asians have a lower risk of MS than whites or why the higher risk of MS among blacks was found only among women.
GLOSSARY
- CI=
- confidence interval;
- CIS=
- clinically isolated syndrome;
- ICD-9=
- International Classification of Diseases, ninth revision;
- MS=
- multiple sclerosis
Footnotes
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Supplemental data at www.neurology.org
- Received September 19, 2012.
- Accepted in final form January 24, 2013.
- © 2013 American Academy of Neurology
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