Prevalence of multiple sclerosis in key cities of Brazil. A study in Joinville, Southern Brazil

The Brazilian Committee for Treatment and Research in Multiple Sclerosis (BCTRIMS) has launched an initiative to determine the prevalence of multiple sclerosis (MS) in Brazil, based on key cities deemed representative of their regions in terms of demographic and environmental features.

To investigate the prevalence rate of MS in Joinville.

We reviewed the medical records of all patients who lived in Joinville and met the 2010 McDonald's diagnostic criteria revised for MS on the prevalence day (March 11, 2016). Potential MS patients included individuals treated by all practicing neurologists in the city and the ones found in patients' association and the database of the Municipal Department of Health. Advertisements about the survey were also broadcast on radio and television. Patients who were not living in Joinville on the prevalence day were excluded. All potential MS patients were invited to an in-person diagnostic review, carried out by a panel of experienced neurologists with special expertise in MS on March 11, 2016.

The MS prevalence rate was 13.5 per 100,000 inhabitants (95% confidence interval [95%CI] 12.9-14.0/100,000). A total of 51 (66.2%) participants were females, and 26 (33.7%) were males (female to male ratio=1.9:1). Out of the 77 patients, 73 (94.8%) were Caucasians, and four (5.1%) were mixed-race.

Despite its latitude location and European colonization, the prevalence rate was below expectation. The intense internal migration from regions with lower MS prevalence rates to Joinville may have played a role in attenuating the increased risk of MS associated with latitude gradient and European ancestry. Prevalence studies in other cities from Southern Brazil with no significant internal migration and taking part in this broad project may clarify this issue.