The risk of Parkdinson's disease rose threefold for people with traumatic brain injuries (TBI) who lost consciousness for more than an hour.
But TBI was not associated with Alzheimer's disease.
"If there were a signal there across the three studies we really should have seen it, and we didn't," says study investigator Paul Crane, MD, MPH, Alzheimer's researcher at the University of Washington, Seattle to Scientific American.
A meta-analysis published online in the journal JAMA Neurology shed new light on the relationship between TBI and neurodegeerative disorders. Researchers reviewed three separate studies that followed 7,130 participants over a 10-year period. Nearly 1,600 of those participants consented to an autopsy, allowing clinicians to examine the brain in addition to annual or biennial cognitive and clinical testing.
Prior research is limited, and divided, on the relationship of TBI and Alzheimer's. Most used clinical criteria to confirm participanys had Alzheimer's, though the difference between Alzheimer's and dementia is difficult to observe while the person is still living. Autoposies are more accurate for distinguishing neurodegenerative disorders.
But this study looked only at people with TBI and late-onset Alzheimer's. Early-onset Alzheimer's, which has been included in prior research, was beyond the scope. Still, the lack of associations suggests the relationship with TBI and dementias stll needs to be better understood. Research into the different types of Alzheimer's could explain the differet findings.
The study focused on people who suffered one TBI incident, not chrnoic traumatic encephalopathy (CTE) common among athletes liek Mouhammad Ali who suffer multiple, repeated brain injuries.