A new study finds that traumatic brain injury from a blow to the head, with loss of consciousness, may increase a person’s risk of developing Parkinson’s disease (PD) later in life. The results appear in the July 11 online edition of JAMA Neurology. The researchers did not find an association between head injury and Alzheimer's disease.
The neurological effects of head injuries are much in the news, with worry over repeated, relatively mild, concussions among athletes, and with the recent death of boxing great Muhammad Ali, who lived with Parkinson's disease. This new study, however, focused narrowly on the long-term effects of even one instance of trauma to the head — especially injuries involving loss of consciousness — among older people more representative of the general population.
Researchers led by Paul K. Crane, M.D., M.P.H., at the University of Washington in Seattle, analyzed self-reported data, collected between 1994 and 2014, from 7,130 people who had enrolled in other studies that gathered data on memory, cognition and aging. On average, study participants were 80 years old at the time of this report, and did not have dementia, PD, or Alzheimer’s disease when they enrolled in the original studies. Forty percent were men. Brain tissue was examined on autopsy for 1,589 participants, to search for signs of PD and Alzheimer’s disease.
- Eight hundred sixty-five study participants reported having had a traumatic brain injury with loss of consciousness at some time in their lives.
- During the time study participants’ health was followed, 117 new cases of PD were diagnosed among the total of 7,130 participants.
- A past traumatic brain injury with loss of consciousness longer than an hour was associated with three and a half times increased risk of developing PD.
- History of traumatic brain injury was also associated with the accumulation of Lewy bodies in brain cells, the toxic clumps of alpha-synuclein protein that are the hallmark of PD.
- Traumatic brain injury was not associated with mild cognitive impairment (MCI)|, dementia, Alzheimer’s or brain changes associated with Alzheimer’s.
- Microinfarcts — microscopic strokes in the brain that may be a cause of dementia — were found more often in the brains of people who had traumatic brain injury that lost consciousness for more than one hour.
What Does It Mean?
Head injuries are common, even among non-athletes. Earlier studies have suggested that they might be related to developing Alzheimer’s.
But the new research found instead that just one traumatic brain injury with loss of consciousness of more than one hour was associated with Parkinson’s, and not Alzheimer’s. Although most people recover to normal functioning after a traumatic brain injury, this study suggests that the consequences from even a single head injury may take decades to develop.
The finding underscores the importance of preventing head injuries. It also suggests that additional research to understand the relationship between brain injury and Parkinson's, and why they are linked, might provide ideas for possible interventions for reducing risk of PD.
Beth Vernaleo Ph.D., Associate Director of Research Programs, PDF added, “While previous research has linked head injuries to neurodegenerative disease, this study illustrates a more specific finding — that a single blow to the head causing a loss of consciousness for more than an hour, even in one’s 20s, may lead to a three-fold increased risk of Parkinson’s decades later. Although the vast majority of people who experience head injury will not develop Parkinson’s, this study may provide clinicians with an additional diagnostic tool. For example, asking patients about history of head injury, amongst other symptoms and risk factors, may prove a valuable means of ascertaining the likelihood of a PD diagnosis.”