The incidence of clinically isolated syndrome in a multi-ethnic cohort.

The purpose of this study was to determine the incidence of clinically isolated syndrome (CIS), a potential precursor of multiple sclerosis (MS), and whether it varies by race/ethnicity in a multi-ethnic, population-based cohort. We conducted a retrospective cohort study of over 9 million person-years of observation from the multi-ethnic, community-dwelling members of Kaiser Permanente Southern California Health Plan from January 1, 2008 to December 31, 2010. Incidence of CIS and risk ratios comparing incidence rates between racial/ethnic groups were calculated using Poisson regression. We identified 468 newly diagnosed CIS cases that did not meet McDonald criteria for MS. The average age at diagnosis was 39.0 years (range 2.7-85.8) and 68.8% were women. The female preponderance was more pronounced among black (75.7%) and Hispanics (70.5%) than in white and Asian individuals with CIS (66.5 and 54.5%, respectively; P = 0.14). The most common presenting symptom in Hispanics was optic neuritis (P = 0.008), and in blacks, transverse myelitis (P = 0.07). Incidence of CIS was lower in Hispanics (3.8, 95% CI 3.2-4.4, P < 0.0001) and Asians (2.4, 95% CI 1.5-3.6, P < 0.0001) and similar in blacks (6.8, 95% CI 5.3-8.5, P = 0.30) compared with whites (5.9, 95% CI 5.1-6.7). The incidence of CIS varies by race/ethnicity and sex in a similar pattern to MS. In addition, the clinical presentation of CIS varies by race/ethnicity. These findings strengthen the probability that the old belief that blacks have a decreased risk of MS is no longer true. These findings highlight that studies that include minorities are likely to lead to important insights into the etiology and prognosis of CIS and MS.