Last Updated: 2007-10-08 18:20:17 -0400 (Reuters Health)

NEW YORK (Reuters Health) – A history of head injury is associated with an increased risk of developing amyotrophic lateral sclerosis (ALS), according to results of a study published in the October 1st issue of the American Journal of Epidemiology.

"Clinical observations and case-control studies have suggested that physical trauma may be associated with a higher risk of ALS, but the evidence is far from conclusive," write Dr. Honglei Chen and his associates.

The research team, led by Dr. Chen at the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, studied 109 ALS patients, diagnosed between 1993 and 1996, and 255 matched controls. The participants were asked if they had ever been injured so severely that they had required medical attention, and if so, how many times and at what ages.

Overall, 46.8% of cases and 45.1% of controls reported ever experiencing a severe physical injury that required medical attention. Only head injury was associated with an elevated risk of developing ALS (odds ratio = 1.4), the researchers found.

Compared to subjects without head injury, those with repeated head injuries and those with head injuries within the last 10 years before diagnosis had significantly increased risks of ALS (OR = 3.1 and 3.2, respectively).

Subjects with repeated head injuries with the latest occurring in the last 10 years had an 11-fold higher risk of ALS than those without head injury.

The investigators observed that patients with head injuries had an earlier age at ALS diagnosis than those without previous head injuries (54.0 years versus 59.5 years).

Taken together, the results are "consistent with a recent observation of higher ALS risk among Italian soccer players, and may thus suggest that repeated head injury is a risk factor for ALS," Dr. Chen told Reuters Health.

"ALS is very rare and our results were based on a small number of cases," he pointed out. "It is therefore important to confirm this association with a large number of cases, hopefully in a prospective study."

Am J Epidemiol 2007;166:810-816.