STOCKHOLM — People who experience a concussion during adolescence are at significantly elevated risk for multiple sclerosis (MS) later in life, especially 15 years or more following their head trauma, a large retrospective study suggests.

This risk for developing MS over time nearly doubled in this population compared with people without a history of concussion.

"We also found a significantly increased risk among males and not females" starting at about 8 years post-concussion in a secondary analysis, lead study author Christopher Povolo, BSc, of the Department of Clinical Neurological Sciences, Schulich School of Medicine & Dentistry at Western University in London, Ontario, Canada, told Medscape Medical News.

The findings were presented during a poster session here at the 35th Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) 2019.

Previously, other investigators linked head trauma, including concussion, with MS.

For example, a Swedish case control study presented at ECTRIMS in 2017 showed adolescents with one concussion diagnosis were at elevated risk to develop MS (odds ratio [OR], 1.22; 95% confidence interval [CI], 1.05 - 1.42; P = .008).

The study, published the same year in Annals of Neurology, revealed the risk was even greater among those with two or more concussion diagnoses (OR, 2.33; 95% CI, 1.35 - 4.04; P = .002).

In the current research, Povolo and colleagues studied the correlation between concussions in adolescents age 11 to 18 years and future MS using information from several linked Canadian databases. They assessed 391,860 people, including 97,965 diagnosed with a concussion as adolescents.

The concussed group presented to an emergency department in Ontario between 1992 and 2011. The investigators matched each of these cases to three unaffected individuals, adjusting for age, sex, address, and index date.

Those who developed MS had one or more related hospitalizations or five or more relevant ICD codes for physician billing within 2 years.

Primary and Secondary Outcomes

The researchers report no overall increased risk of MS within 15 years of follow-up among those with a history of adolescent concussion.

In contrast, the same group had a significantly elevated risk of developing MS at 15 years or longer (hazard ratio [HR], 1.85; P = .005), according to a stratified Cox regression analysis.

A secondary analysis showed a difference by sex. Males exposed to concussion as teenagers had an increased risk for MS earlier, at 8 or more years of follow-up (HR, 1.58; P = .02). Females showed no such significantly increased risk.

Povolo and colleagues also tried a more sensitive definition for developing MS: three or more hospital or physician claims using all available years of data. In this case, all participants regardless of sex had an increased risk of MS (HR, 1.37; P = .008) if they had at least 8 years of follow-up since their concussion.

The investigators would like to expand their research in this area. "In the future, we could make it longer, or use a countrywide database," Povolo said.

"All Is Fine With Their Data"

A main message of the research is "prevention and the risk during adolescence," Tomas Olsson, MD, PhD, a professor of neurology affiliated with the Department of Clinical Neuroscience, Center for Molecular Medicine, Karolinska Hospital in Stockholm, told Medscape Medical News when asked to comment.

"So tough sports like boxing, ice hockey, American football may not be good in relation to MS, probably mainly for those having parents with MS," he added.

Olsson was coauthor of the 2017 study in Sweden that reported similar associations between adolescent concussion and risk of future MS. "Basically their findings replicate our own, which were published a couple of years ago. So I think all is fine with their data."

Support for the study was provided by a Roche Canada unrestricted, investigator-initiated trial grant and research funding from the Swedish Research Council, Knut and Alice Wallenberg foundation, and the Swedish Brain Foundation. Povolo has disclosed no relevant financial relationships. Olsson reported unrestricted MS research grants and compensation for advisory boards and/or lectures from Biogen, Genzyme, Novartis, AstraZeneca, and Allmiral.

35th Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) 2019: Abstract P396. Presented September 11, 2019.

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