Irregular arm swing points to Parkinson’s

PENN STATE (US) — An asymmetrical arm swing—where one arm swings less than the other—is an early sign of Parkinson’s and can be seen in time to begin drugs and other interventions in time to slow the disease’s progression.

No cure for Parkinson’s disease exists, but researchers say if taken early, certain drugs can improve some of the disease’s symptoms and even reduce the likelihood of death, making early diagnosis important. Changes in nutrition and other lifestyle factors may also modify the progression of the disease.

For the study, published in Gait & Posture, researchers attached inexpensive accelerometers to the arms of eight Parkinson’s disease patients who were in the early stages of the disease—within three years of clinical diagnosis. They also attached the accelerometers to the arms of eight age- and sex-matched people who did not have the disease.

Subjects then walked continuously for about eight minutes at a comfortable pace. Researchers then downloaded the acceleration data and used software they developed—that will be available free to interested doctors—to analyze it.

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“Scientists have known for some time that people with Parkinson’s disease exhibit reduced arm swing during the later stages of the disease, but no one had come up with an easy way to measure this,” says Stephen Piazza, associate professor of kinesiology at Penn State.

“We found that not only do people with the disease exhibit reduced arm swing, but they also exhibit asymmetric arm swing, and this asymmetric arm swing can easily be detected early in the disease’s progression.”

Piazza and colleagues noted significantly higher acceleration asymmetry, lower cross-correlation between the arms and reduced synchronization of the arms in the early Parkinson’s disease patients.

The lower cross-correlation and reduced synchronization suggest that the arm movements are poorly coordinated, says Joseph Cusumano, professor of engineering science and mechanics.

“In other words, if I measure the location of your right arm, it is difficult to use that measurement to predict the location of your left arm,” he says. “It is well known that Parkinson’s disease has an impact on how people move—neurologists have been using this fact as the basis for clinical examinations for a very, very long time—but here we are for the first time precisely quantifying how the disease not only affects the relative amount of limb movements, but also how well coordinated in time these movements are.”

To diagnose patients with Parkinson’s disease early, some doctors and scientists have proposed the use of a smell test, because people with the disease lose their ability to distinguish odors, according to Xuemei Huang, movement disorders physician at the Penn State Milton S. Hershey Medical Center. “But conditions other than Parkinson’s disease also can affect a person’s ability to smell,” she says.

The new method of evaluating arm swing can be applied quickly and inexpensively by primary care physicians in their own offices when the smell test is inconclusive and before the application of an expensive brain scan.

“Measuring arm swing asymmetry and coordination with our method may be the cheapest and most effective way to detect Parkinson’s disease early in patients’ lives when it still is possible to treat the symptoms of the disease and to improve longevity,” says Piazza.

The scientists plan to further investigate whether the arm swing evaluation in combination with a smell test can enhance early diagnosis even more.

They also plan to further develop their technique so that the accelerometers give immediate readings, which would save the extra step of downloading the data to a computer and analyzing it, thereby making the arm swing assessments of Parkinson’s disease even easier.

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