Palm-Worn Device May Help in Tracking Changes in Rigidity After DBS, Study Says

A palm-worn device can quantify joint stiffness in Parkinson’s disease patients by tracking changes in rigidity following treatment with deep brain stimulation, and may be of use in measuring fluctuations in motor symptoms, scientists who created the tool report.

Their study, “A Palm-Worn Device to Quantify Rigidity in Parkinson’s Disease,” was published in the Journal of Neuroscience Methods.

Most Parkinson’s patients — at least 89%, the study states — have problems with rigidity, which results in stiffness and makes movement arduous.

Clinically, rigidity is defined as resistance to passive movement — movement that is performed by another person without voluntary motion by the patient — and measured by an expert who moves the “wrist, elbow, and knee joints about their full range of motion and subjectively grades resistive force,” the researchers wrote.

Clinical assessment of rigidity in Parkinson’s patients is largely subjective, due to observer-dependent scoring of muscle stiffness based on The International Parkinson and Movement Disorder Society-Sponsored Revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS).

Automatic devices hold the potential of objectively measure a patient’s increased resistance to passive movement.

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Researchers at the Bionics Institute and the University of Melbourne in Australia developed the Bionics Institute Rigidity Device (BiRD), a palm-worn apparatus that uses a miniature motor to trigger an automatic flexion of the hand’s third digit at the metacarpophalangeal joint — the joint at the base of each finger.  Transducers then record data on flexion and extension forces, allowing investigators to quantify rigidity.

Their intent was to establish a more objective measure of a patient’s resistance to passive movement.

The team chose to validate the device against the MDS-UPDRS and demonstrate BiRD’s sensitivity to the therapeutic impact of deep brain stimulation (DBS), a surgical treatment of motor symptoms.

Eight Parkinson’s patients (six men and two women, ages 47–59) and 16 healthy individuals, serving as controls, were recruited to test the device.

Two experienced physiotherapists assessed patients’ rigidity according to the MDS-UPDRS. Individuals were instructed to draw a large imaginary circle in the air using their contralateral arm. Evidence shows that contralateral movement, i.e. moving the side of the body that’s not being evaluated — for instance, moving the right hand instead of the left — substantially increases rigidity in Parkinson’s patients.

Patients had their DBS device on, but were off dopaminergic medication; each had stopped such medication the night before the test.

“Participants were familiarized with the device [BiRD] and a practice trial was conducted prior to formal assessment. Each rigidity assessment consisted of 15 continuous extension/flexion cycles applied without removing the device,” the study said.

In the Parkinson’s group, rigidity of both arms was measured first using the BiRD, and then by the two physiotherapists (using the MDS-UPDRS). Patients’ deep brain stimulation device was then turned off, and rigidity quantified using the new device every 10 minutes for an hour.

DBS treatment was then resumed, and rigidity was measured by BiRD at five-minute intervals for half an hour. “At the last trial within this period, the two raters also assessed rigidity,” researchers wrote.

In the control group, dominant hand stiffness was assessed using BiRD while people were at rest or performing a contralateral activation task. In these people, 10 evaluation cycles were performed: five at rest and five during activation maneuver (movement).

Measurements obtained with BiRD were moderately similar to those recorded with MDS-UPDRS. The device was able to identify the impact of DBS therapy on rigidity by detecting differences between on- and off-DBS states.

The device was also able to distinguish differences between contralateral activation exercises, as well as among participants with and without Parkinson’s disease.

Stiffness in Parkinson’s patients gradually increase during an hour after the DBS device was turned off. Rigidity was almost immediately eased by resumption of deep brain stimulation treatment.

“Given its ability to track changes in rigidity due to therapeutic intervention, our technique could have applications where continuous measurement is required or where a suitably qualified rater is absent,” the researchers concluded.