Neurologists in the US suggest irregular arm swings while walking could be an early sign of Parkinson’s disease and scientific measurement of such a suspected symptom could help diagnose the disease earlier, giving greater opportunity to slow brain cell damage and disease progression.

The study is the work of Dr Xuemei Huang, associate professor of neurology, Penn State Hershey College of Medicine, and colleagues, and a paper on it is published in the current issue of Gait and Posture.

Parkinson’s disease is an age-related disorder where the person loses certain types of brain cell, has slow speech and impaired and irregular movements.

Huang told the press that:

“The disease is currently diagnosed by tremors at rest and stiffness in the body and limbs.”

“But by the time we diagnose the disease, about 50 to 80 percent of the critical cells called dopamine neurons are already dead,” she added.

Disease experts already know that “the later stages of Parkinson’s disease (PD) are characterized by altered gait patterns”, wrote the authors.

Decreased arm swing while walking is the most frequently reported motor dysfunction in people with Parkinson’s, and yet altered gait patterns in the upper body are not as well documented as for the lower body in the early stages of the disease.

So Huang and colleagues decided to compare arm swing magnitude and asymmetry in patients with and without Parkinson’s and produce some measures that could help with early assessment of the disease.

“We know that Parkinson’s patients lose their arm swing even very early in the disease but nobody had looked using a scientifically measured approach to see if the loss was asymmetrical or when this asymmetry first showed up,” explained Huang.

Huang and colleagues tested their assumption, that because Parkinson’s is an asymmetrical disease, the arm swing on one arm will be lost first compared to the other.

For the study, using an optically-based motion capture system, the researchers measured the arm swing of 12 people who had three years earlier been diagnosed with Parkinson’s, and also of eight people in a control group.

The motion capture system entailed the participants wearing many reflective markers and then being tracked by eight digital cameras that captured the exact position of each main part of the body while walking.

Special software analyzed data from the camera images:

“When a person walks, the computer was able to calculate the degree of swing of each arm with millimeter accuracy,” explained Huang.

The Parkinson’s patients were in “off” state when the measurements were done: that is they stayed off their medication overnight to stop it affecting the test results.

The participants were asked to walk at a normal and a fast pace, and then on their heels (to minimize push off).

“Arm swing was measured as the excursion of the wrist with respect to the pelvis,” wrote the authors, who compared arm swing magnitude for each arm, as well as inter-arm symmetry between the Parkinson’s group and the control group.

The results showed that:

  • Both groups had comparable gait velocities.
  • There was no significant difference between the Parkinson’s group and the control group in the size of arm swing in all walking conditions for the arm that swung more or less.
  • However, what was striking was that compared to the control group, the Parkinson’s group showed significantly greater asymmetry in their arm swing (one arm swung significantly less than the other while walking).
  • The Parkinson’s group asymmetry angle was 13.9 ± 7.9 per cent compared to 5.1 ± 4.0 per cent for the control group (p = 0.003).
  • When the participants walked faster, the arm swing increased but the amount of asymmetry stayed the same.

Huang and colleagues concluded that:

“Unlike arm swing magnitude, arm swing asymmetry unequivocally differs between people with early PD and controls.”

“Such quantitative evaluation of arm swing, especially its asymmetry, may have utility for early and differential diagnosis, and for tracking disease progression in patients with later PD,” they suggested.

Huang said they believed this was the first time that arm swing has been shown to be a potentially early sign of Parkinson’s disease.

While people without Parkinson’s show some irregular arm swing when they walk, the asymmetry is much larger in those who have the disease, said the researchers.

Huang said this could be a useful way to help early detection of Parkinson’s:

“There are wide scale efforts to find drugs that slow cell death. When they are found, they could be used in conjunction with this technique to arrest or perhaps cure the disease because they could be given before great damage has occurred,” she explained.

The study was funded by the National Institutes of Health and the University of North Carolina Center for Human Movement Sciences.

“Arm swing magnitude and asymmetry during gait in the early stages of Parkinson’s disease.”
Michael D Lewek, Roxanne Poole, Julia Johnson, Omar Halawa, Xuemei Huang
Gait & Posture, 2009, In Press, Corrected Proof, Available online 27 November 2009

Source: Penn State.

Written by: Catharine Paddock, PhD