Is head trauma a risk factor for amyotrophic lateral sclerosis? An evidence based review

Our objective was to evaluate the epidemiological literature regarding the association between trauma to the head and ALS, in order to determine if trauma to the head is a risk factor for ALS. A Medline literature search was conducted for the period between 1980 and October 2010 using the search terms: ('head trauma' OR 'head injury') AND (ALS OR 'amyotrophic lateral sclerosis' OR MND OR 'motor neuron disease'). The references of primary articles and reviews were checked to assure completeness of the search. Articles with primary data and reference groups were reviewed. The American Academy of Neurology evidence based method for classification of evidence for inferring causality and assigning level of conclusion was used. Twelve of 14 articles published since 1980 met the inclusion criteria. One class II article and three class III articles showed an association between a single instance of head trauma and ALS that did not exceed what might be seen due to chance alone. Eight class IV evidence articles could not inform conclusions. We concluded that evidence based analysis of the epidemiologic literature does not permit concluding that a single instance of head trauma is a risk factor for, or causes, ALS (Level U conclusion).