Prianka Waghray, BA, Brandel France de Bravo, MPH
Studies have shown that people with traumatic brain injuries (TBI) are at higher risk for Parkinson’s disease, and that exposure to pesticides also increases the risk of Parkinson’s. A recent study concludes that people who reported traumatic brain injury and had exposure to paraquat—a chemical used to kill weeds and other plants—were three times more likely to develop Parkinson’s disease than other people. Traumatic brain injury was defined as a loss of consciousness for more than 5 minutes.
Methods used in the Study
From 2001 to 2011, researchers interviewed 357 Parkinson’s patients and 754 people from the general population in Central California who otherwise matched the Parkinson’s patients. Participants were asked to report if they ever experienced a head injury with a loss of consciousness for more than 5 minutes. Using a tracking system that measures chemicals in the environment, researchers assessed participants’ exposure to paraquat based on where they lived and where they worked between 1974 and 1999. Paraquat is an herbicide that can only be applied by licensed professionals. It is not the type of weed killer used in people’s backyards; it is used in farming, which is why the researchers chose the agricultural area of Central California.
For some time, scientists have speculated that a traumatic brain injury might make the brain more vulnerable to certain chemicals in pesticides and herbicides, thereby worsening the effects of exposure to them. The findings of the Central California study suggest that head injury and paraquat exposure combine to damage dopamine-producing cells located in the brain. Dopamine cells enable a person’s motor functions. When these cells are damaged, a person’s motor functions can be permanently impaired. While dopamine cells were damaged by head injury and paraquat exposure alone, more cells were damaged when traumatic brain injury was accompanied by exposure to paraquat.
What is Parkinson’s Disease?
Parkinson’s disease is one of the most common nervous system disorders and affects 1-2% of the population over 65 years of age. Parkinson’s is a chronic neurological disorder, which means that it affects a patient’s nervous system and gets worse over time.
A person with Parkinson’s may have difficulty walking, chewing, speaking, and moving their arms and legs. There are four (4) common symptoms associated with Parkinson’s:
- Tremors and trembling hands, legs, jaw and arms
- Stiffness of the arms, legs and body
- Inability to move fast
- Lack of balance and coordination
Other symptoms include cognitive impairment and emotional changes, including depression.
There is no one cause of Parkinson’s disease, and environmental exposures may contribute to developing the disease.
Other risk factors for Parkinson’s include:
- Being over the age of 50: The single biggest risk factor is growing old.
- Your genes: Parkinson’s is known to run in families. Scientists suspect a genetic link.
- Gender: Men are more likely to develop Parkinson’s than women.
When should you be concerned?
Has everyone with Parkinson’s had a brain injury, been exposed to paraquat, or both? No: Parkinson’s happens after brain cells that make dopamine have been damaged. Damage to brain cells occurs for different reasons in different people. More research is needed on the percentage of Parkinson’s cases that can be explained by the combination of traumatic brain injury and exposure to paraquat. Also, the study’s findings are most relevant to people who live or work in agricultural areas where paraquat is used. People in urban areas, for instance, are unlikely to have the same level of exposure to this herbicide.
Is there anything you can do?
While there is no cure for Parkinson’s, there are ways you can slow the onset of symptoms:
- Exercise: There is evidence that exercise improves balance and coordination, helping Parkinson’s patients stay limber for longer.
- Reduce stress: Studies show that stress worsens every symptom of Parkinson’s.
- Social support: Having a support system, including family, friends, and other Parkinson’s patients, can help individuals cope with the disease.
For Parkinson’s patients whose symptoms cannot adequately be treated by medication, researchers are working on other treatment options, including Deep Brain Stimulation (DBS), a surgically implanted medical device that helps control movement and balance for Parkinson’s patients.  DBS, approved by the Food and Drug Administration in 2002, is designed to block nerve signals that cause tremors, shaking, and other symptoms of Parkinson’s.
Studies show that DBS can curb some symptoms in patients with advanced Parkinson’s, but the treatment also has risks. A 2009 study published in JAMA (the Journal of the American Medical Association), found that by 6 months after surgery, patients receiving DBS had gained, on average, four and a half more hours per day of good symptom control, while patients receiving standard medical care showed no change in symptom control. Patients with DBS also had significant improvements in quality of life as compared to patients receiving standard medical care, who had almost no change in quality of life over the six-month study period. On the other hand, the DBS patients experienced many more moderate to severe side effects than the patients receiving standard care, particularly in the first three months. Patients with the surgically implanted device were more likely to fall, have gait disturbances, dyskinesia (problems with controlling movement), motor dysfunction (problems with movement ), problems with balance, experience depression, and suffer from dystonia, a disorder which causes muscles to contract uncontrollably and the body to contort. The most common problem for DBS patients (about 10% of patients) was infection at the site of the surgery, requiring antibiotics and sometimes the removal of all or part of the device.
If patients taking medication showed no improvement, does that mean medication doesn’t work? One goal of the medication, apart from controlling symptoms, is to delay the worsening of symptoms, so “no change” is a type of success. And why did the patients who underwent surgery report an improved quality of life, given the increase in serious side effects? One possibility is that patients who had surgery wanted to believe that their lives had improved. Another possible explanation is that a larger proportion of patients benefit from the surgery than the percentage that will experience serious harm. The bottom line is that patients considering the surgery need to know the risks and decide whether they are worth taking. To help them do that, more research is needed to determine if the benefits of DBS truly outweigh the risks for most patients. If only some patients truly benefit, then it is important to know which patients those are.
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 National Institute of Neurological Disorders and Stroke. NINDS deep brain stimulation for Parkinson’s disease information page. 7, February 2012. Retrieved at http://www.ninds.nih.gov/disorders/deep_brain_stimulation/deep_brain_stimulation.htm.
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