Incidence and prevalence of multiple sclerosis in the Americas: a systematic review.

BACKGROUND: The incidence and prevalence of multiple sclerosis (MS) varies considerably around the world. No previous study has performed a comprehensive review examining the incidence and prevalence of MS across the Americas. The purpose of this study was to systematically review and assess the quality of studies estimating the incidence and/or prevalence of MS in North, Central and South American regions. METHODS: A comprehensive literature search was performed using MEDLINE and EMBASE from January 1985 to January 2011. Search terms included 'multiple sclerosis', 'incidence', 'prevalence' and 'epidemiology'. Only full-text articles published in English or French were included. Study quality was assessed using an assessment tool based on recognized guidelines and designed specifically for this study. RESULTS: A total of 3,925 studies were initially identified, with 31 meeting the inclusion criteria. The majority of studies examined North American regions (n = 25). Heterogeneity was high among all studies, even when stratified by country. Only half of the studies reported standardized rates, making comparisons difficult. Quality scores ranged from 3/8 to 8/8. CONCLUSION: This review highlights the gaps that still exist in the epidemiological knowledge of MS in the Americas, and the inconsistencies in methodologies and quality among the published studies. There is a need for future studies of MS prevalence and incidence to include uniform case definitions, employ comparable methods of ascertainment, report standardized results, and be performed on a national level. Other factors such as sex distribution, ethnic make-up and population lifestyle habits should also be considered.