Background: Multiple sclerosis (MS) is one of the most common neurological disorders and a leading cause of nontraumatic disability in young adults in many countries. Recent reports from the Middle East and North Africa have suggested a moderate to high risk of MS in these countries. Methods: A literature search was performed in August 2014 in MEDLINE, EMBASE, and IMEMR to retrieve original population-based studies on MS epidemiology in the Middle East and North African countries published between 1st January 1985 and 1st August 2014. We designed search strategies using the key words: MS, prevalence, incidence, and epidemiology. According to the inclusion criteria, 52 studies were included in this systematic review. Results: McDonald's criteria were the most widely used diagnostic criteria in the studies. Most studies were conducted in single hospital-based centers with a defined catchment area. The female/male ratio ranged from 0.8 in Oman to 4.3 in Saudi Arabia. MS prevalence ranged from 14.77/100,000 population in Kuwait (2000) to 101.4/100,000 in Turkey (2006). The overall MS prevalence in the region was 51.52/100,000. The mean age at disease onset ranged from 25.2 years in Kuwait to 32.5 years in Northeastern Iran, with an overall estimate of 28.54 years. Conclusions: Recent advances in MS registries will allow nation-wide studies and temporal comparisons between countries, provided that age- and sex-standardized estimates are available.

<b><i>Background:</i></b> Multiple sclerosis (MS) incidence has dramatically increased in Tehran, Iran. The health impact of air pollution in Tehran underscores the attention to a possible association to this environmental risk factor. In this study, the authors aimed to analyze the spatial distribution of prevalent MS cases and their association with the spatial patterns of air pollution. <b><i>Methods:</i></b> Patient records meeting McDonald's criteria for definite MS diagnosis with disease onset during 2003-2013 were obtained. Next, the location of 2,188 patients was successfully geo-referenced within Tehran metropolis by geographic information system (GIS) bureau of Iran's post office based on their phone numbers. A cluster analysis was performed using the average nearest neighbor index (ANNI) and quadrat analysis. The long-term exposures of MS patients to particulate matter (PM₁₀), sulfur dioxide (SO₂), nitrogen oxide (NO), nitrogen dioxide (NO₂), and nitrogen oxides (NOx) were estimated using the previously developed land use regression models. <b><i>Results:</i></b> Prevalent MS cases had a clustered pattern in Tehran. A significant difference in exposure to PM₁₀, SO₂, NO₂, and NOx (p < 0.001) was observed in MS cases compared with controls. <b><i>Conclusion:</i></b> This study revealed the potential role of long-term exposure to air pollutants as an environmental risk factor in MS.

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