Objective: To evaluate whether participating in physical contact sports is associated with a release of neurofilaments and whether this release is related to future clinical neurological and/or psychiatric impairment.

Methods: We have performed a systematic literature review of the PubMed, MEDLINE and Cochrane Library databases using a combination of the search terms neurofilament(s)/intermediate filament and sport(s)/athletes. Only original studies, written in English, that have reported on neurofilament measurements in CSF and/or serum/plasma of physical contact sport athletes were retained for data extraction. This review was conducted following the Preferred Reporting Items for Systematic Review and Analyses guidelines.

Results: Eighteen studies reporting on light chain neurofilament (NfL), in eight different contact sports (i.e. boxing, American football, ice hockey, soccer, mixed martial arts, lacrosse, rugby and wrestling), matched our inclusion criteria. In 13/18 athlete cohorts, significant NfL elevations in CSF or serum/plasma were described, as compared to situations of non-exposure. Most compelling evidence was present in boxers and American football players, where marked and/or immediate exposure-related increases were appreciable at the intra-individual level in exclusive cohorts, generally paired with control groups who were well-described and matched for age. Findings in others sports were less suitable to draw conclusion upon. No studies were encountered that have investigated the relationship with the targeted clinical endpoints. 

Conclusion: Nfl release can be seen, as a potential marker of neuronal brain damage, in participants of physical contact sports, particularly boxing and American football. The exact significance regarding the risk for future clinical impairment remains to be elucidated.