Combined measures of movement and force variability distinguish Parkinson’s disease from essential tremor

ObjectiveTo examine whether behavioral and electrophysiological measures of motor performance accurately differentiate Parkinson’s disease (PD) and essential tremor (ET).MethodsTwenty-four patients (12 PD; 12 ET) performed isometric force, ballistic movements, and tremor tasks. Receiver operating characteristic (ROC) analyses were conducted on all dependent measures that were significantly different between the two patient groups.ResultsPatients with PD were more impaired on measures of movement deceleration than ET. Patients with ET were more impaired on measures of force variability than PD. ROC analyses revealed that sensitivity and specificity were excellent when combining measures during the isometric force task (torque rise time and force variability; 92% sensitivity and 92% specificity; AUC = 0.97). When combining measures across the force and movement tasks, the ROC analysis revealed improved sensitivity and specificity (force variability and peak deceleration; 92% sensitivity and 100% specificity; AUC = 0.99).ConclusionsCombining measures of force variability and movement deceleration accurately differentiate patients with PD from those with ET with high sensitivity and specificity.SignificanceIf validated in a larger sample, these measures can serve as markers to confirm the diagnosis of PD or ET and thus, enhance decision making for appropriate treatments for patients with these respective diseases.

► Essential tremor patients were more impaired on measures of isometric force variability than Parkinson’s disease patients.
► Combining force variability with torque rise time could differentiate Parkinson’s disease from essential tremor.
► Combining force variability with movement deceleration further discriminated Parkinson’s disease from essential tremor.