Epidemiology

There were an estimated 2 million prevalent cases of MS globally in 2016.[10] The estimated prevalence of MS in the US adult population in 2010 was 309.2 per 100,000, representing over 727,000 cases.[11] Both the incidence and the ascertainment (i.e., diagnosis using more sensitive and specific investigations) of MS are felt to be rising globally and in the US.[10]

MS is most commonly diagnosed in people between 20 and 40 years old. However, it can occur in children as young as 2 years, where it may be confused for acute disseminated encephalomyelitis. It is occasionally diagnosed in people in their sixth or seventh decade who may have been asymptomatic for years. The estimated 2010 prevalence of MS in the US was highest in people aged 55 to 64 years.[11]

There is a significantly skewed sex ratio, with a female to male ratio of around 3:1, and the disparity appears to be increasing.[11][12]

A geographic gradient, with higher incidence at latitudes closer to the poles, has been linked with MS.[11][13] People of European descent are most commonly affected, but affected black Americans may have more aggressive courses due to a combination of socioeconomic and genetic factors, as well as later diagnosis.[14] The highest prevalence rates are reported in high-income North America, western Europe, and Australasia, with the lowest in eastern sub-Saharan Africa, central sub-Saharan Africa, and Oceania, although accurate data are not available for many parts of the world.[10]

Approximately 80% to 85% of people with MS have a relapsing course; in the other 10% to 15% the disease is progressive from onset (primary progressive MS).[15]

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