Increased Arm Swing Asymmetry Points to Parkinson's Disease

Researchers at Pennsylvania State University (Hershey, USA) measured forearm accelerations while eight early PD subjects and eight controls performed 8-minute walking trials. Arm swing asymmetry (ASA), maximal cross-correlation (MXC), and instantaneous relative phase (IRP) of bilateral arm swing were compared between PD and Controls. The correlations between arm swing measurements (ASA and MXC) and the Unified PD Rating Scale (UPDRS) scores were then estimated.

The results showed significantly higher acceleration asymmetry, lower cross-correlation between the arms, and reduced synchronization of the arms in the early PD patients, who demonstrated significantly higher ASA and lower MXC than the controls. The IRP probability distribution for PD was significantly different from controls, with an angular standard deviation of 67.2° for PD and 50.6° for the controls. Among PD subjects, ASA was significantly correlated with the UPDRS score for the limbs, whereas MXC was significantly correlated with the tremor subscore of the limbs. According to the researchers, the lower cross-correlation and reduced synchronization suggest that the arm movements in PD patients are poorly coordinated. The study was published in the December 2011 issue of Gait & Posture.

“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,” said lead author associate professor of kinesiology Stephen Piazza, PhD. “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.”

Early diagnosis of patients with Parkinson's can also be done with a smell test, since people with the disease lose their ability to distinguish odors; the smell test is however inconclusive, since conditions other than PD can also affect the ability to smell. The researchers are planning to investigate further whether the arm swing evaluation in combination with a smell test could enhance early diagnosis even more.

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