Traumatic head injury and ALS linked, but relationship still unclear: Review
People with history of such injuries nearly 50% more likely to be diagnosed
Written by |
- Traumatic head injury is linked to a nearly 50% higher chance of ALS, with a stronger association observed in men.
- Multiple head injuries were not associated with a higher chance of ALS relative to single injuries.
- Causality is unclear; early, undiagnosed ALS might increase fall risk, leading to head injuries, not vice versa.
There is an association between traumatic head injuries and amyotrophic lateral sclerosis (ALS), but the nature of this relationship remains unclear, according to a review and meta-analysis of published studies.
People who had a history of a traumatic head injury were nearly 50% more likely than those without head injury to have an ALS diagnosis, researchers found. However, multiple head injuries were not associated with a higher chance of ALS relative to single injuries, suggesting that the link between the two conditions may be more complex.
“The association between THI [traumatic head injury] and ALS does not feature dose-response relationship which weakens the association and does not suggest causality [cause-and-effect],” researchers wrote.
In addition, most studies lacked evidence that traumatic head injury preceded ALS, supporting the hypothesis that early, undiagnosed ALS may increase risk of falls and injuries, which may, therefore, be an early sign — not a cause — of ALS.
“Future studies that increase their sample size and representativeness of the population, adjust for [potential influencing] variables and demonstrate temporality between the exposure [THI] and the outcome [ALS] are needed,” researchers wrote.
The study, “Head injuries as a risk factor for amyotrophic lateral sclerosis: A systematic review and meta-analysis,” was published in Clinical Neurology and Neurosurgery.
‘The link with ALS is still considered debatable’
ALS is a neurodegenerative disease in which motor neurons, the specialized nerve cells that control voluntary movement, gradually die, leading to a variety of symptoms. There are several well-recognized risk factors for ALS, including genetics and certain environmental exposures.
One potential risk factor is traumatic head injury, or a violent blow to the head that can harm the brain. Previous studies have connected traumatic head injury with a variety of neurological conditions, including ALS. “However, the link with ALS is still considered debatable,” the researchers wrote.
To assess these links, a pair of U.S.researchers systematically reviewed studies published through September 2025 on potential associations between head injury and ALS. A total of 17 studies, covering 578,715 people, were included in the final meta-analysis.
Pooled data showed that a history of traumatic head injury was significantly associated with a 54% higher chance of ALS. Data from the 14 studies that adjusted analyses for potential influencing factors showed a 47% higher chance of ALS in people with head injuries. Both analyses showed high variability between the included studies, which may limit conclusions.
To dig deeper into this potential relationship, the team looked at different participant subgroups. Combining results from two studies that broke down their analysis based on sex, the researchers found that head injury was significantly associated with a higher risk of ALS in men (by twofold), but not in women.
“This differential association between trauma and ALS among males compared to females might be a result of the differences in peripheral inflammatory mechanisms involved in the two sexes,” the researchers wrote. “It was previously highlighted that males are more susceptible to oxidative stress [a type of cellular damage] and have higher [first-line] immune activation compared to females.”
In this context, a head injury, which also triggers inflammation, could have a greater effect on men’s nervous systems.
Undiagnosed ALS may increase risk of head injuries
Significant associations between head injury and ALS were also found across geographical regions and when the team included only data from the 12 high-quality studies.
“Interestingly, subgroup analysis according to the frequency of THIs did not find a difference in the association with the risk of ALS between single THI or multiple THIs,” the team wrote. Specifically, single head injury was significantly linked to a 48% higher chance of ALS, while multiple head injuries were significantly associated with a 34% higher chance.
This lack of dose-response relationship suggests that head injuries may not directly cause ALS. Instead, traumatic head injury “could be the final step in a multi-step model suggesting several steps are needed to trigger ALS and prolonged exposure to several environmental factors combined contributes to ALS development,” the team wrote.
Another possibility is that early, undiagnosed ALS increases the risk of head injuries and not vice versa. Prior studies have suggested that the relationship is strongest for injuries that occur within a year of ALS diagnosis. During this time, unrecognized ALS symptoms could lead to falls, the team noted.
Because 70.6% of the studies lacked evidence that head injury preceded the development of ALS, the researchers weren’t able to determine the relative timing of head injury and ALS diagnosis.
Small sample sizes, poor population representativeness, and incomplete adjustment for potential influencing factors in many studies may also have influenced the results. Moreover, there was significant publication bias, meaning that studies showing a relationship between head injury and ALS were more likely to be published than those that didn’t.
Because of these limitations, the researchers stressed the need for more research into the interplay between head injury and ALS. Studies following up participants over time and “with large sample size that adjust for [potential influencing] variables and demonstrate temporality of the evidence are needed,” they concluded.
Leave a comment
Fill in the required fields to post. Your email address will not be published.