The association between upper limb motor performances and gait dynamics in essential tremor: an emerging relationship

Essential tremor (ET) is a complex disorder extending beyond upper limb action tremor. Both slowing in upper limb movements and impaired gait performances have been widely described. The present study aimed to assess clinical-instrumental relationship between wearable-sensor recorded upper limb motility, tremor and walking performances in ET and explore their role in disease characterization. A gyroscope taped over the index finger was used to quantify both tremor in three tasks (forward outstretched; lateral-wing; instrumental finger-nose, iFN) and upper limb performances in the iFN. Maximum speed (MS) and time (going phase; approaching phase) were used as indices of upper limb motility. Explorative correlation analyses were used to assess the relationship between walking and upper limb metrics. Regression analysis - using synthetic indices of walking (WPC1) and turning performances (TPC1) obtained with PCA - were applied to confirm the association adjusting for possible confounders. Thirty patients were considered for the analyses (23 men, 76.7%; mean age ± SD: 71.9 ± 5.1). No significant correlation between tremor and kinematic parameters was found. Consistent correlations were found between upper limb kinematics and gait performances. Both WPC1 and TPC1 were significantly associated with MS. The study identified an association between upper limb motor performances and gait dynamics in ET, suggesting a possible expression of a shared motor-control pathway, at least partly independent from the tremor network. Moreover, the potential role of a simple, rapid and clinically-scalable, wearable sensor-based protocol applicable both in tremor quantification and as a potential marker of broader motor function in ET was also highlighted.