Why Use Immersive Virtual Reality to Assess Gait in Functional Motor Disorders?

Background: Functional motor disorders (FMD) are disabling conditions modulated by attentional demands. Immersive virtual reality (iVR) engages multiple attentional and sensory networks, but its application in people with FMD (PwFMD) remains limited. Objective: We investigated whether iVR modulates spatiotemporal gait parameters in PwFMD differently from people with Parkinson's disease (PwPD) and healthy controls (HC). Methods: Wearable insoles tracked spatiotemporal gait parameters in the PwFMD (n = 30), the PwPD (n = 32), and HCs (n = 42) across three real-world (C1-C3) and three iVR (C4-C6) walking conditions with increasing cognitive and sensory load. Discriminative performance was evaluated using receiver operating characteristic (ROC) analysis, whereas group and condition effects were examined using repeated-measures analysis of variance (ANOVA) adjusted for age, sex, and body mass index (BMI). The dual-task effect (DTE) quantified the impact of cognitive load. Results: In the iVR condition (C4-C6), gait speed, stride length, and swing-time variability discriminated both PwFMD and PwPD from the HCs with good accuracy (AUC > 0.8), particularly under higher dual-task load (C5 and C6), whereas no parameter reliably differentiated the PwFMD from the PwPD using ROC analysis (AUC < 0.7). Adjusted ANOVA revealed significant group × condition interactions for multiple gait parameters (P < 0.05). DTE analysis revealed distinct responses to cognitive load: dual-task cost was greater in PwPD than in PwFMD, which was often comparable to the HCs, particularly under cognitive dual-task conditions (C3 and C6). Conclusions: iVR revealed context-dependent gait abnormalities and differential responses to cognitive load in PwFMD and PwPD, which suggests its use as a paradigm to probe underlying mechanisms. © 2026 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.