Over the past ten years, there have been many epidemiological studies on MS in Iran indicating an increase in the prevalence of MS. Initial studies took place in Isfahan and Mazandaran provinces. The prevalence of MS was 20.1 per 100,000 people in Mazandaran Province (582 cases) in 2007. The average age of patients was 34.3 years, and the female to male ratio was 2.6(4). In the present study, it can be seen that the prevalence of MS in Mazandaran is 72.5 per 100,000 people, which shows an increase of roughly 3.5 times. The average age of the patients increased four years and reached to 38.5, and the ratio of women to men, by 0.3 increase, estimated at 2.9.
In Isfahan province which is located in central Iran, the prevalence of MS disease was 35.5 per 100,000 in 2006, and the average age of the patients was 32.5 years with a female to male ratio of 3.6(5). A more recent study in 2014 showed a 1.5-fold increase in the prevalence of this disease with 54.5 MS patients per 100,000 and a drop in the sex ratio of 0.3 since 2006 in the same region. (11) There was no MS patient under 15 years old. These findings suggest potential role of puberty period on the onset of pathogenesis of MS that noted in another study as well. (12)
In 2009, a research project on MS showed a prevalence of 50.57 in 100,000 people for this disease in Tehran. The female to male ratio was 3.1l, and the mean age of MS patients was 35.48 years in this study (13). Izadi found the prevalence of 72.1 in 100,000 people in Fars province in 2015 for this disease with female to male ratio of 4.04 (a prevalence of 116.5 in women and 28.3 in men) (14). A review article, published in “the International Journal of Epidemiologic Research” in 2018, showed a sharp increase in the prevalence of MS up to 95 per one hundred thousand since 2013(15).
Our study showed a lower prevalence for MS in Mazandaran compared to other provinces of Iran with a lower latitude while, we expected Mazandaran, as a northern province, to have a higher prevalence of MS. Different factors can be contributing to a relatively lower estimation of the prevalence of MS in Mazandaran despite its higher latitude. One possible explanation for this difference can be the referral pattern of patients of neighbouring provinces to the study centres to access tertiary healthcare facilities. Because of the proximity of Mazandaran province to Tehran, the capital of Iran, with a significantly higher number of health care facilities, we can see a tendency in Mazandaran MS patients to follow their treatment in Tehran. Additionally, Rasht, the capital of Gilan province, might be more accessible for some of the patients in the western regions of Mazandaran.
Numerous studies have reported a similar increasing trend in the prevalence of MS in many other countries around the world. In 2002, Pugliatti et al. estimated the prevalence of MS in northern and western Europe to be under 170 per 100,000 population (16). This figure increased to more than 200 in one hundred thousand in Kingwell et al. study in 2013. (17). In Canada, there has been a dramatic increase in the prevalence of MS from 157 in 1996 to 265 per hundred thousand population in 2013(18). In the United States, the MS prevalence rate was estimated at 85 per 100.000 people in 2002 (19), while, eight years later, studies conducted in three different regions of the United States, showed an increase of up to 109 per 100,000 population in the prevalence of this disease (20).
Although these findings hypothesized the sunlight and UV role in the pathogenesis of MS, but many studies did not support this hypothesis. In the study of Ofer Amram and et al., the life time UVB exposure estimated by new satellite technology. (21) There was no significant associatiation between the age MS onset and calculated UVB exposure. (22)