Quantitative assessment of wrist rigidity in Parkinson's disease by using built-in sensors of a smartphone

Abstract

Rigidity is one of the motor symptoms of Parkinson’s Disease (PD) which is described as an increased muscle tone that occurs throughout the entire range of mo tion of a limb. Clinical assessment of rigidity is highly subjective; it depends on the experience of the examiner. In this thesis, wrist rigidity is evaluated numerically by using data obtained from the accelerometer, gyroscope and capacitive touch screen of a smartphone. Due to lack of a built-in force sensor, a novel gadget has been devel oped to be used as a force sensor on the phone screen. The gadget is calibrated to convert the number of pixels to force values. Subsequently, a set of experiments were performed to measure rigidity with the phone. Totally, 11 healthy and 10 PD pa tients participated in the clinical experiments. Rigidity measurements were performed on the right wrist of the subjects, and scores were assessed according to the Unified Parkinson’s Disease Rating Scale (UPDRS) obtained by neurologists before the clinical trials. Experiments were conducted with and without a contralateral hand movement (Froment’s Maneuver). In addition, the experiments were conducted in “on” and “off” conditions. “On” condition refers the improvement of symptoms by the administration of anti-parkinsonian medications, “off” condition refers the aggravation of symptoms due to withdrawal of medications. The results have shown that the method can assess the severity of wrist rigidity according to the UPDRS rigidity scale in a confidence interval of 95%. The rigidity scores of the patients in the “off” condition were found higher than the “on” condition (α = 0.05). In addition, performing a contralateral hand maneuver aggravated the rigidity (α = 0.05). Considering the results, the method can be adopted clinically to assess rigidity.