Review of studies on boxing and CTE
Generally, it seems like more bouts is correlated with more brain damage and related symptoms, but scientists don't really know how/why.
Some points:
- In 1920's people first started noticing boxers in "punch drunk" state. Basically CTE symptoms
- Pre-clinical CTE: more susceptible to head blows, worse reaction times
- Most common symptoms are slurred speech, abnormal gait
- "Neuropsychological tests" are one way to diagnose brain damage. These are tests of attention, memory, hand-eye coordination, etc
- Interestingly, one study using neuropsychological tests found no correlation between number of bouts and performance
- Another study comparing 20 active amateur boxers with 20 non-boxer controls over 9 years found no evidence of neuropsychological decline or CTE
- Authors note that many studies on the topic do not control for drug and alcohol use
- CT scan based study found strong correlation between number of bouts and number of abnormalities in the scan. No correlation between number of KO's and TKO's and abnormalities. Suggests damage is from repeated non-KO punches.
- Another larger study of 338 active professional boxers found "normal" CT scans in 93% and "borderline" atrophy in 7% of scans
- MRI studies might be more accurate, comparison studies show that CT scan can be normal but issues show up on MRI
- There are only small MRI studies, some of which don't show abnormalities in the boxers they studied (n=10 or so), and some of which do
- Authors note that because these studies typically are not done over the course of a career, it's hard to say whether the damage is from boxing, or other reasons (drugs/alcohol perhaps)
- Electroencephalography (EEG) abnormalities show up in about 50% of boxers diagnosed with CTE. But other studies don't show confirm this
Overall, conclusion is, boxing probably causes brain damage, probably from repeated punches to the head, but we don't really know much about it, can't diagnose it with precision, and certainly can't treat it.