Traumatic Brain Injury Accelerates Onset by 5 Years, Study Suggests
Experiencing a traumatic brain injury (TBI) is associated with an earlier age of Parkinson’s onset, but not with more severe disease-associated nerve cell loss or younger age of death, a study suggests.
These findings, presented at the 2021 Alzheimer’s Association International Conference in Denver and online, suggest that TBI, a well-established risk factor for Parkinson’s, may lower the threshold of brain damage leading to the development of symptoms, the researchers noted.
The study, “Traumatic brain injury accelerates Parkinson’s disease onset without altering Parkinson’s neuropathology,” was published in Alzheimer’s & Dementia.
Parkinson’s is caused by the progressive loss of dopamine — one of the brain’s major signaling molecules — due to the malfunction and death of dopamine-producing nerve cells in substantia nigra, a brain region involved in the control of voluntary movements.
It is believed that this loss of dopamine and dopamine-producing nerve cells must cross a certain threshold before the symptoms of Parkinson’s become noticeable.
Traumatic brain injury is “a well-established risk factor for Parkinson’s disease (PD),” the researchers wrote.
A previous study reported that veterans with TBI — regardless of its severity, defined through the duration of loss of consciousness — had a 71% higher likelihood of developing Parkinson’s than other vets.
However, “the nature of this relationship remains unclear,” the researchers wrote.
Now, a team of researchers in the U.S. evaluated whether TBI is associated with age of disease onset, survival, and severity of substantia nigra neurodegeneration by retrospectively analyzing data from the National Alzheimer’s Coordinating Center (NACC) database.
NACC, the largest resource of its kind in the U.S., collects demographic, clinical, and autopsy-derived brain data from people ranging from cognitively normal to mildly cognitively impaired to demented. TBI status was assessed based on self-reported history.
The potential link between traumatic brain injury and age of onset and survival was investigated through the analysis of data from 423 Parkinson’s patients: 53 with a history of TBI and 370 without such head trauma. Participants’ visits occurred between 2005 and 2018.
Nerve cell loss in the substantia nigra was assessed by analyzing autopsy information from 1,133 people (150 with TBI), who were selected without regard to their prior diagnoses.
Results showed that traumatic brain injury was associated with a 4.9-year earlier age of Parkinson’s onset. The 10 patients with TBI-associated loss of consciousness for more than five minutes showed Parkinson’s symptoms a mean of 9.9 years earlier than those without any previous head trauma. This reflected a significantly increased risk of Parkinson’s by nearly three times.
Patients who reported a history of TBI also lived a mean of 5.9 years longer than those without head trauma, but there was no significant association with age of death.
In addition, a history of traumatic brain injury, regardless of the unconsciousness period, was not associated with greater substantia nigra damage in autopsies.
Traumatic brain injury “appears to accelerate PD onset without altering death age or PD-related [nerve cell damage],” the researchers wrote.
“This relationship suggests that TBI lowers the threshold required for PD [nerve cell damage] to present as symptomatic PD,” they added.