A new UK-wide study has found that people who experience a traumatic brain injury may face a higher short-term risk of developing MND. However, this increased risk appears to be temporary, limited to the first two years after injury, suggesting that rather than causing the disease, traumatic brain injury may sometimes occur as an early consequence of undiagnosed, underlying MND.

These findings provide important new insights into the complex relationship between head injury and neurodegenerative disease and highlight the need for caution when interpreting the link between trauma and MND risk.

Studying a large population

Led by Dr Xingxing Zhu at the University of Glasgow, the research team analysed electronic health records from more than 340,000 adults across the UK between 2005 and 2020. The study included 85,690 people with a recorded history of TBI (traumatic brain injury) and 257,070 matched individuals from the general population with no such history.

Participants were followed for a median of almost six years, providing over 2.1 million person-years of follow-up data. During this time, 150 new ALS cases were identified across the cohort.

Risk peaks within two years of injury

Although the researchers found that TBI was more common in people with ALS, importantly, this association was time-dependent: the rate of ALS diagnosis was more than six times higher within the first two years after a TBI but returned to baseline levels thereafter.

This suggests that, in some and possibly all cases, the injury may not directly cause ALS but could instead reflect the effects of early, subtle disease symptoms. This could include balance problems or coordination changes that increase the likelihood of falls and injury before diagnosis.

The study found no significant differences in the age at diagnosis or death between people with and without a history of TBI.

Why is this important?

While previous studies have suggested that repetitive head impacts or severe TBIs might raise the risk of developing neurodegenerative diseases, the evidence for ALS has been inconsistent. This large-scale, population-based study helps to clarify the picture.

By showing that the association between TBI and ALS is limited to a short window after injury, the findings suggest reverse causality as a possible explanation, meaning the injury could occur due to early disease changes, not cause them.

The authors emphasise the importance of future studies that track individuals over more extended time periods and capture detailed information on all head injuries, including mild cases that may not require hospital treatment.

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Original study:
Zhu X, Russell ER, Lyall DM, Ho F, Mackay DF, Pell JP, Stewart W. Traumatic Brain Injury and Risk of Amyotrophic Lateral Sclerosis. JAMA Network Open. 2 October 2025; 8(10): e2535119. DOI: 10.1001/jamanetworkopen.2025.35119