In many cases by the time Parkinson's disease is diagnosed, irreparable damage is already done.

But now, new research by a team of neurologists finds that the manner in which people walk -- including irregular arm swings -- may be a very early marker for the disease.

"This type of early detection research will be critical to advancing the science of therapeutic interventions hoping to slow disease progression," National Parkinson Foundation spokesman Peter N. Schmidt told "Further, the National Parkinson Foundation is supporting the introduction of such quantitative measures and has launched a major initiative around tracking the progression of such measures throughout the course of the disease."

Parkinson's is an age-related disorder involving loss of certain types of brain cells and marked by impaired movement and slow speech.

Xuemei Huang, associate professor of neurology at the Penn State Hershey College of Medicine, believes this kind of early detection may help physicians apply treatments to rein in further brain cell damage until strategies to slow disease progression are available.

"The disease is currently diagnosed by tremors at rest and stiffness in the body and limbs," Huang says. "But by the time we diagnose the disease, about 50 to 80 percent of the critical cells called dopamine neurons are already dead."

The new research, findings of which appear in the current issue of Gait and Posture, confirms Huang's clinical impression that in people with Parkinson's, one arm swings much less than the other as a person walks.

"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," says Huang.

"Our hypothesis is that because Parkinson's is an asymmetrical disease, the arm swing on one arm will be lost first compared to the other," Huang adds.

The researchers compared the arm swing of 12 people diagnosed three years earlier with Parkinson's, with eight people in a control group.

The Parkinson's patients were asked to stop all medication the night before to avoid influencing the test results.

The team used special equipment to measure movement accurately, including reflective markers on the study participants and eight digital cameras that captured the exact position of each segment of the body during a walk.

"Images from the cameras were sent to a computer where special software analyzed the data" explains Huang. "When a person walks, the computer was able to calculate the degree of swing of each arm with millimeter accuracy."

Analysis of the magnitude of arm swing, asymmetry, and walking speed revealed that the arm swing of people with Parkinson's has remarkably greater asymmetry than people in the control group; one arm swung significantly less than the other in the Parkinson's patients.

When the participants walked at a faster speed, the arm swing increased but the corresponding asymmetry between them remained the same.

"We believe this is the first demonstration that asymmetrical arm swings may be a very early sign of the disease," says Huang.

While slightly irregular arm swing occurs in people without Parkinson's, the asymmetry is significantly larger in those suffering from the disease.

"Our data suggests that this could be a very useful tool for the early detection of Parkinson's," notes Huang.

"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."