BACKGROUND: Mild traumatic brain injury (TBI) or concussion is common in many 
sports. Today, neuropsychological evaluation is recommended in the monitoring of 
a concussion and in return-to-play considerations. To investigate the 
sensitivity of neuropsychological assessment, we tested amateur boxers post bout 
and compared with controls. Further the relationship between neuropsychological 
test results and brain injury biomarkers in the cerebrospinal fluid (CSF) were 
investigated.
METHOD: Thirty amateur boxers on high elite level with a minimum of 45 bouts and 
25 non-boxing matched controls were included. Memory tests (Rey Osterrieth 
Complex Figure, Listening Span, Digit Span, Controlled Word Association Test, 
and computerized testing of episodic memory), tests of processing speed and 
executive functions (Trail Making, Reaction Time, and Finger Tapping) were 
performed and related to previously published CSF biomarker results for the 
axonal injury marker neurofilament light (NFL).
RESULTS: The neurological assessment showed no significant differences between 
boxers and controls, although elevated CSF NFL, as a sign of axonal injury, was 
detected in about 80% of the boxers 1-6 days post bout. The investigation of the 
relationship between neuropsychological evaluation and CSF NFL concentrations 
revealed that boxers with persisting NFL concentration elevation after at least 
14 days resting time post bout, had a significantly poorer performance on Trail 
Making A (p = 0.041) and Simple Reaction Time (p = 0.042) compared to other 
boxers.
CONCLUSION: This is the first study showing traumatic axonal brain injury can be 
present without measureable cognitive impairment. The repetitive, subconcussive 
head trauma in amateur boxing causes axonal injury that can be detected with 
analysis of CSF NFL, but is not sufficient to produce impairment in memory 
tests, tests of processing speed, or executive functions. The association of 
prolonged CSF NFL increase in boxers with impairment of processing speed is an 
interesting observation, which needs to be verified in larger studies.