RECENT evidence has revealed a complex and time-dependent association between traumatic brain injury (TBI) and risk of amyotrophic lateral sclerosis (ALS), according to a large UK cohort study. Individuals with documented TBI showed a higher incidence of ALS, but the increased risk was limited to the two years following injury and then returned to baseline levels.
ALS Risk and Traumatic Brain Injury
By analysing health records from 85,690 people with TBI and 257,070 matched controls, researchers found that the ALS risk was more than doubled in the TBI group overall (hazard ratio 2.61, 95% CI 1.88-3.63). However, closer inspection revealed this risk peaked in the first two years after injury (HR 6.18, 95% CI 3.47-11.00), then faded, aligning with rates seen in the general population. These findings indicate that some TBIs may actually reflect the early effects of subclinical ALS, a concept known as reverse causality—where the neurological changes of undiagnosed ALS may lead to falls and accidents.
What Do These Results Mean?
Researchers note these results expand on earlier, smaller studies which linked repeated head injuries in contact sports to later neurodegeneration. In the general population, such associations are complex; genetic and environmental factors likely interact in ALS development, and early neuronal vulnerability may precede clinical presentation. The findings emphasise that surveillance for neurological symptoms in TBI patients could help identify early ALS, rather than suggesting TBI as a direct cause.
Next Steps for ALS and TBI Research
While the overall absolute risk of ALS remains low, the study recommends careful assessment of people with TBI for the early signs of motor neuron disease. Further research should investigate whether particular injury patterns or genetic predispositions might clarify the relationship between TBI and ALS onset and progression
Reference
Zhu X et al. Traumatic brain injury and risk of amyotrophic lateral sclerosis. JAMA Netw Open. 2025;8(10):e2535119.
