MONDAY, May 19, 2003 (HealthDayNews) -- People who suffer a severe head injury with a loss of consciousness and memory may be at greater risk of developing Parkinson's disease later in life, a new study suggests.
"We found a link between head trauma and the future development of Parkinson's disease," says study author Dr. James H. Bower, of the Mayo Clinic. Patients who had mild head trauma -- that is, trauma without loss of consciousness or only a brief episode of memory loss -- did not have an increased risk for developing Parkinson's, he adds.
But people who had moderate or severe head trauma -- trauma with a loss of consciousness or a prolonged episode of memory loss, a skull fracture or bruising on the brain -- appeared to have an 11-times greater risk of developing Parkinson's, Bower says.
"What was surprising was that these people only had one head trauma and on average this head trauma occurred 20 years before the development of Parkinson's," he notes.
Bower and his Mayo Clinic colleagues studied 196 people who developed Parkinson's. These patients were compared with healthy people from the general population. In both groups, the researchers looked at complete medical records, including incidents of head trauma, according to their report in the May 20 issue of Neurology.
Bower's team came up with three possible explanations for their findings. One is that when you suffer head trauma, the blood-brain barrier is disrupted and certain poisons from the bloodstream, such as a virus or toxins, get into the brain, triggering a cascade that leads to cell death. "But it can take 20 years before symptoms develop," Bower speculates.
Another possibility is that the trauma causes brain cells to produce new proteins that can lead to cell death, he says.
"The third, and least likely possibility, is that after a head trauma, some cells are lost, and over time with normal aging and cell death, it reaches a point when Parkinson's develops," Bower says.
"We are not suggesting that head trauma is a cause for Parkinson's disease," he says. "This is one cause among many, including genetic predisposition and other environmental factors."
Parkinson's affects about 1.5 million people in the United States, with some 50,000 new cases diagnosed each year. While Parkinson's can start at any age, it is most common among adults over 50 years of age.
A chronic neurological condition, Parkinson's is characterized by symptoms ranging from tremors on one side of the body to slowness of movement, stiffness of limbs and balance problems.
Bower notes that some boxers, such Muhammad Ali, suffer from dementia pugilistica, which is similar to Parkinson's. Although the patients in his research did not suffer from dementia pugilistica, the study findings suggest there is a link between trauma and symptoms of Parkinson's.
"The findings of our study are another reason to emphasize the importance of wearing protective head gear when playing sports," Bower says.
"By identifying the various causes of the disease, we can look for the commonality between the causes and what that means in the development of Parkinson's," he adds.
Dr. Miguel A. Hernan of the Harvard School of Public Health calls the new study "interesting."
"Risk factors identified in epidemiologic studies are helpful to generate hypotheses about the mechanisms that lead to disease," he says. "These hypotheses can be tested in the lab. Eventually, such research may result in a better understanding of the causes of disease and, perhaps, even in methods to prevent it."
"The problem with Parkinson's disease is that very few risk factors have been identified in epidemiologic studies," Hernan says. "Adding head injury to the list will definitely open new lines of basic research. I look forward to experiments that will test the hypotheses put forward by the authors."
More information
To learn more about Parkinson's disease, visit the Parkinson's Disease Foundation or the National Library of Medicine.
