Are you at risk for Parkinson's disease?

An estimated one million people in the United States are living with Parkinson’s disease (PD). Nearly 90,000 people are diagnosed each year, according to the Parkinson's Foundation. Men are twice as likely to have the condition as women. Public awareness of PD has grown in recent decades, as celebrities like actor Michael J. Fox have chosen to address it publicly. Fox was diagnosed in 1991 at the age of 29.

Early symptoms of Parkinson’s disease may be barely noticeable. But, with time, this central nervous system disorder progresses, causing a range of symptoms. These may include:

• Tremor: Shaking in the hands, arms, legs, or head
• Rigidity: Stiff limbs and muscles
• Postural instability: Trouble with balance and coordination
• Bradykinesia: Slowness of movement, which may also include a reduction in facial expressions

Researchers know that Parkinson's develops due to the death of nerve cells in a part of the brain called the basal ganglia. These cells coordinate muscle movement. Once too many of these cells are gone, the remaining ones can no longer produce enough of a vital chemical messenger called dopamine, which brain cells use to communicate.

Unlike Fox, most people who develop PD do so after age 60. (An estimated 5 to 10 percent of cases appear before the age of 50.) But besides age, risk factors that contribute to disease development have not been as clear.

What we know about Parkinson's risk factors

Research has suggested that certain environmental toxins may contribute to the development of PD. These chemicals may act on the body either alone or in interaction with our genes. But the results of studies have often been inconclusive, says Jill Giordano Farmer, DO, MPH, director of the Parkinson’s Disease and Movement Disorders program at the Global Neurosciences Institute in New Jersey.

In studying twins, Dr. Farmer notes, researchers have found differences in the development of PD based on their exposure to industrial solvent chemicals over time. Those with greater exposure had higher rates of Parkinson’s. But the connection requires further research and confirmation.

Study results about genetic risk factors have also not been definitive. Only about 15 to 25 percent of people with PD have a family history of the disease. Mutations (or errors) in several genes have been identified. Still, genetic factors, when they are present, are considered rare, says Farmer. They carry a low risk of penetrance, or being passed from one generation to another.

“So, there really are no risk factors that are modifiable (or changeable),” at least at this time, Farmer says. “We do not tell patients to avoid certain foods or to be on certain diets or to take certain supplements. The data just isn’t there.”

Instead, healthcare providers (HCPs) advise patients to follow general rules of good health, like eating a diet high and fruits and vegetables, as well as these:

Use protection if working with chemicals

In her own practice, Farmer asks patients about their exposure to Agent Orange, a herbicide widely used to destroy trees and plants during the Vietnam War. The chemical has been linked to some cancers and other diseases, including PD.

Veterans with Parkinson's disease who were also exposed to Agent Orange during their service are eligible for health care and disability compensation from the U.S. Department of Veterans Affairs (VA) without proving a direct connection between their disease and service. Some research also shows an increased risk of PD in people exposed to certain pesticides (chemicals used to kill insects).

Avoid repetitive head trauma as much as possible

Even mild traumatic brain injury (TBI) is associated with a higher risk of Parkinson’s disease later in life. One study published in Neurology in 2018 compared roughly 163,000 Veterans who experienced mild TBI to Veterans of a similar age who had not. Compared to those with no TBI, the Veterans with mild TBI had a 56 percent higher risk of developing Parkinson’s disease. Though the individual level of risk was seen as low, the authors called the association between TBI and PD the "highest level of evidence” yet discovered.

Diagnosing Parkinson’s disease

Early diagnosis of PD is still considered difficult because there are no blood or laboratory tests that are definitive. But based on medical history and a physical exam, Farmer says, HCPs still can make fairly accurate diagnoses.

For an HCP to consider a diagnosis of Parkinson’s disease, bradykinesia (slow movements) must be present. Additionally, a patient must display one or more of these symptoms:

• Shaking in a limb while at rest
• Stiffness of the arms, legs, or torso
• Difficulty with balance

Afterwards, HCPs look to see how the patient responds to dopamine replacement.

“If there’s improvement in motor symptoms,” Farmer says, “that gives us our answer.”

Brain scans are generally not helpful in making a diagnosis of PD. But certain types of scans, such as magnetic resonance imaging (MRI) of the brain, may be used to help confirm a diagnosis or to rule out other conditions that may resemble PD.

Farmer and other neurologists are working to understand and better manage PD. Scientists, meanwhile, continue to work toward identifying biomarkers (indicators of disease) that would allow for earlier diagnosis and treatment of PD. As with cancer, the hope is to tailor treatments to each individual and to stay ahead of worsening disease.

Parkinson's disease treatment: the present and future

Parkinson’s disease is not yet curable. But medical treatments, and in some cases, surgery, can bring symptom relief to patients, sometimes for many years.

The primary medicine taken for PD is called levodopa. It helps increase levels of dopamine in the brain. Patients may also take other medicines to boost dopamine and reduce involuntary movements, tremors, and muscle stiffness.

If medicines aren’t effective, a procedure called deep brain stimulation is also an option. After electrodes are implanted in the brain, an electrical current is used to stimulate areas of the brain to help prevent PD symptoms.

Anything that can best mimic continuous levels of dopamine offers the greatest benefit for easing symptoms, says Farmer. That can mean either electronically (through deep brain stimulation) or through dopamine-modulating drugs taken orally or under the skin, she says.

What holds the greatest promise, Farmer says, involves research efforts to identify disease-modifying therapies that can stop or reverse the degeneration that occurs once Parkinson’s disease takes hold.

“We’re not there yet,” she says, “but researchers are looking into these mechanisms.”