The prevalence of Multiple Sclerosis (MS) has increased worldwide. As of 2020, 2.8 million people are estimated to live with MS globally. This represents a 30 percent increase as compared to 2013. Let’s look at how these numbers break down.
Prevalence in the U.S.
MS prevalence in the United States also shows a parallel increase to the global trend. In an article published in 2019, the estimated 2008-2010 prevalence of MS in the U.S. was 310 per 100,000 people, or an approximate 730,000 patients. Previous estimates published in 2013 from data collected from 1985 to 2011 estimated closer to 400,000 MS patients in the U.S. That reported change represents an 83% increase.
Break-Out by Gender and Region
Broken down by gender, the more recent data reveals a lopsided female to male ratio of 2.8. Put simply, MS patients are almost three times as likely to be women. As far as age, the prevalence of MS was highest in the age group of 55- to 64- year-olds.
An examination of MS prevalence by geography reveals some clear trends. More cases are found in the northern hemisphere. Notably, Canada has also seen a dramatic increase in the prevalence of MS. In contrast, a 2005 study (with less robust data collection methods) showed Panama to have a prevalence of only 5.2 per 100,000. The comparison between Canada in northern North America, and Panama, just north of the equator is stark.
However, when you compare the 2013 and 2019 studies, the skews in both gender and north-south geographic gradient were similar. In other words, although the absolute number of MS patients has increased, the dominant proportion of females and those who live in more northern regions is consistent between the two studies.
Incidence Versus Prevalence of MS
As we dig deeper into the studies, it’s important to understand the terminology used in reporting disease population. “Prevalence” and “incidence” are different. Prevalence is defined as proportion of persons who have a specific health condition at a specific time. Incidence is defined as the proportion of persons who develop a condition during a particular time.
Incidence Among Racial Groups
The incidence of MS in white populations over the last half-century has been stable or increased only slightly. In contrast, MS incidence in selected racial groups has increased significantly. Compared to the white population, incidence of MS has been higher in blacks and lower in Hispanics and Asians. However, MS incidence among black women drives the overall increase among blacks. Black women have a higher risk of MS, while black men have a similar risk as whites. Notably, MS prevalence in black women was greater than white, Hispanic, and Asian women. (Source).
What Factors Drive the Changes?
These results beg the question: why?
While the answer is not certain, there are several factors to consider.
First, improved diagnosis may increase reported incidence. MS is often diagnosed earlier now due to both the changing definitions of the types of MS, and widespread use of better neuroimaging.
Second, improved data collection techniques and increased access to healthcare may augment data accuracy. Especially in the U.S, it has been challenging to determine incidence and prevalence for chronic diseases, including MS. The lack of a unified health system and a limited ability of the infrastructure to identify and track patients across their lifespan curtails accurate data. However, recent improvements in data collection through surveys, registries, and administrative health claim datasets have increased accuracy of prevalence and incidence rates.
Last, as the cause of MS is not understood, contributing factors for its rise are difficult to identify definitively. But some theories exist. Various environmental and lifestyle factors are thought to affect the incidence of MS. That includes Vitamin D levels, geography, smoking, obesity, as well as the changing gut “microbiome.”
In fact, gut microbiome is the subject of many studies today. Certain gut bacteria create more inflammation in the body. An enrichment or depletion of some gut bacteria in MS patients may play an important role in the development of MS. Furthermore, ongoing studies demonstrate that some MS disease-modifying drugs that change the levels of some gut bacteria suppress the disease. The results suggest the potential use of drug-modifying therapies to treat MS. Source.
More on Gut Microbiomes in our next blog.