WASHINGTON—Researchers and policy makers estimated that 300,000 to 400,000 people in the U.S. had multiple sclerosis in 2010, but new data indicates that number grossly undercounted the number of people affected by the neurological disease.
Surveillance data published in Neurology this spring indicates that that the actual numbers in 2010 were double the previous estimate. Using a new methodology, researchers at the VA and in the MS Prevalence Workgroup determined that about 727,000 individuals had MS at the beginning of the decade and that the number now approaches one million.1
How could so many people be missed?
Nationally, “we simply do not have a good surveillance network for neurological disease,” explained Mitchell Wallin, MD, MPH, director of the MS Center of Excellence-East, based in Washington, DC, and associate professor of neurology at George Washington University and the University of Maryland School of Medicine.
“We haven’t had a good prevalence study in 50 years,” Wallin told U.S. Medicine, and it turns out, “MS is more common than we thought.”
The study used data from the Optum, Truven Health and Kaiser Permanente Southern California datasets to model rates for privately insured individuals and the Centers for Medicare and Medicaid Services and VA healthcare databases for those covered by government-sponsored insurance programs. Altogether, the databases covered 45% of the U.S. population.
Based on previous studies, the researchers assumed a 5.0% rate of MS among individuals without insurance. The team then applied an algorithm previously validated against medical records in large datasets and healthcare systems to identify individuals with MS in the datasets. To capture cases missed because patients with relapsing disease might not see a healthcare provider during the period studied, the study adjusted for undercounting, as well.
For 2010, the cumulated 10-year prevalence was 309.2 per 100,000 or 450.1 per 100,000 for women and 159.7 per 100,000 for men, demonstrating “a steady rise in the prevalence of MS over the past five decades,” according to the authors.
That rise has been quite substantial. A 1976 prevalence study found a rate of 58 per 100,000 and the National Health Interview Survey pegged the rate at 85 per 100,000 from 199 to 1994. Using more restrictive criteria, another study put the rate at 149 per 100,000 for the 2008 to 2012 period.
The divergence in rates between women and men has also increased sharply.
“The trends have been consistent in many places around the world,” Wallin noted, “with rising prevalence and incidence in women. The ratio was close to 1 to 1 in the World War I generation.” In 1976, women were 1.7 times more likely to develop the disease. In the current study, the ratio is 2.8 to 1.
“We don’t have a great explanation” for the increasing rate in women, Wallin added. “It’s probably too quick to be genetics in 50 years. It’s probably things in the environment that women were not exposed to in earlier generations. It might be a virus that they are exposed to as adolescents.”
Those factors might explain the north-south differential in MS prevalence seen in the current and previous studies in the U.S. and across the world. “MS is a disease of geography,” Wallin said. “It could be an environmental thing going on or maybe a virus spreads more readily when people are together in closed environments.”
Wallin and colleagues expanded on the possible triggers for MS in a global study published recently in The Lance Neurology. While more than 200 alleles have been implicated in the disease, the rapid rise in incidence (globally) and prevalence support environmental factors, they observed. “Prime candidates include infection, such as with the Epstein-Barr virus or other organisms, as the initiator of multiple sclerosis, with the suggestion that infections start in the gut and spread to the [central nervous system].”2
Other risk factors might include lack of sunlight or vitamin D, diet, obesity, changes in the gut microbiome, they said.
Mortality Rates Drop
Two factors underlie the marked increase in the numbers of people with MS. Most significantly, mortality rates for this population have dropped rapidly in recent years. A Canadian study found that mortality rates for MS have declined 30% since the 1990s, Wallin noted.
The decrease in mortality among individuals with MS parallels that seen in the general population over the last several decades, despite a decline in life expectancy seen in the last five years driven by increases in deaths from opioid overdose, suicide, influenza and pneumonia.
Still, “people are living longer across the board,” Wallin said. “You can see that in the mortality data; the average age of the MS population has gone up.”
The improvement in mortality rates can be “attributed some to new medicines, but we’re also treating infection better and increasing mobility,” Wallin added.
The aging of the MS population is particularly notable. The average age at diagnosis is 34 and, until recent decades, people with MS died 20 years or more younger than those without the disease. As a result, it has been seen as a neurological disease of relatively young adults. Now, however, MS reduces life expectancy by just six or seven years and median survival from birth extends into the middle of the eighth decade of life.
“It’s generally a good thing that people are living longer. Now our goal is to improve function and what people can do as they live longer,” Wallin said.
In addition to declining mortality, the number of people diagnosed has increased modestly in recent years, as diagnostic criteria have changed and neuroimaging has risen.
The aging of the population with MS means more people will need disease-modifying medications for a longer period and demand for rehabilitation services and multidisciplinary care will continue to rise.
“Knowing we have an older MS population who will need more support over the course of their lives will affect advocacy and funding of treatment and prevention programs so we can help people stay active and functional longer,” Wallin noted.
Staying on top of changes in incidence and prevalence of neurological and other diseases remains a challenge because of the fractured U.S. healthcare system, patients’ movement between insurers and privacy laws.
“We’re OK with infectious diseases and cancer,” Wallin said, but “for so many diseases, we don’t know how many people have them” in the U.S. or around the world. “That’s an important issue in epidemiology—you want to know these basic numbers to use healthcare resources effectively.”
The algorithm and use of population-based healthcare administrative datasets developed to update the estimates for multiple sclerosis might provide a solution. A national surveillance system is important, too, Wallin said.
“Our goal is to come with an efficient, cost-effective way to monitor disease that could be done every 10 years,” he added. “That will help us understand who’s getting the disease, improve treatment, track incidence and prevalence, and try to prevent it.”
Wallin MT, Culpepper WJ, Campbell JD, Nelson LM, et. Al. US Multiple Sclerosis Prevalence Workgroup. The prevalence of MS in the United States: A population-based estimate using health claims data. Neurology. 2019 Mar 5;92(10):e1029-e1040. doi: 10.1212/WNL.0000000000007035. Epub 2019 Feb 15. PubMed PMID: 30770430; PubMed Central PMCID: PMC6442006.
GBD 2016 Neurology Collaborators. Global, regional, and national burden of neurological disorders, 1990-2016: a systematic analysis for the Global Burden of Disease Study 2016. Lancet Neurol. 2019 May;18(5):459-480. doi: 10.1016/S1474-4422(18)30499-X. Epub 2019 Mar 14. PubMed PMID: 30879893; PubMed Central PMCID: PMC6459001.
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