Smartphone motor testing to distinguish idiopathic REM sleep behavior disorder, controls, and PD

TLDR

Idiopathic REM sleep behavior disorder is a prodromal form of Parkinson disease, yet subtle motor impairments are poorly captured by conventional rating scales. The study aimed to identify smartphone‑derived motor features that could distinguish iRBD from healthy controls and Parkinson disease patients. Researchers collected smartphone sensor data from 334 PD, 104 iRBD, and 84 control participants performing seven motor tasks (voice, balance, gait, finger tapping, reaction time, rest tremor, postural tremor) both in clinic and at home, and used these recordings to classify group membership. The smartphone‑based approach achieved 84.6–91.9% sensitivity and specificity across all pairwise comparisons, with postural tremor, rest tremor, and voice being the most discriminative tasks and reaction time the least.

Abstract

<h3>Objective</h3> We sought to identify motor features that would allow the delineation of individuals with sleep study-confirmed idiopathic REM sleep behavior disorder (iRBD) from controls and Parkinson disease (PD) using a customized smartphone application. <h3>Methods</h3> A total of 334 PD, 104 iRBD, and 84 control participants performed 7 tasks to evaluate voice, balance, gait, finger tapping, reaction time, rest tremor, and postural tremor. Smartphone recordings were collected both in clinic and at home under noncontrolled conditions over several days. All participants underwent detailed parallel in-clinic assessments. Using only the smartphone sensor recordings, we sought to (1) discriminate whether the participant had iRBD or PD and (2) identify which of the above 7 motor tasks were most salient in distinguishing groups. <h3>Results</h3> Statistically significant differences based on these 7 tasks were observed between the 3 groups. For the 3 pairwise discriminatory comparisons, (1) controls vs iRBD, (2) controls vs PD, and (3) iRBD vs PD, the mean sensitivity and specificity values ranged from 84.6% to 91.9%. Postural tremor, rest tremor, and voice were the most discriminatory tasks overall, whereas the reaction time was least discriminatory. <h3>Conclusions</h3> Prodromal forms of PD include the sleep disorder iRBD, where subtle motor impairment can be detected using clinician-based rating scales (e.g., Unified Parkinson9s Disease Rating Scale), which may lack the sensitivity to detect and track granular change. Consumer grade smartphones can be used to accurately separate not only iRBD from controls but also iRBD from PD participants, providing a growing consensus for the utility of digital biomarkers in early and prodromal PD.