Abstract
Objective To examine whether behavioral and electrophysiological measures of motor performance accurately differentiate Parkinson’s disease (PD) and essential tremor (ET). Methods Twenty-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. Results Patients 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). Conclusions Combining measures of force variability and movement deceleration accurately differentiate patients with PD from those with ET with high sensitivity and specificity. Significance If 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.
Highlights
Parkinson’s disease (PD) and essential tremor (ET) are among the most common movement disorders, yet misdiagnoses still occur because both groups can present with action tremor and slowness (Shahed and Jankovic, 2007)
We interpret these results as behaviorally significant if they are in agreement with previous studies in the literature, but we did not include them in the Receiver operating characteristic (ROC) analysis
The ET patients produced more antagonist activity (Qant1 and Qant2) throughout the entire movement when compared to the PD group
Summary
Parkinson’s disease (PD) and essential tremor (ET) are among the most common movement disorders, yet misdiagnoses still occur because both groups can present with action tremor and slowness (Shahed and Jankovic, 2007). There are very few objective diagnostic tests for PD or ET. A potential solution to this would be differentiating PD from ET patients through objective behavioral and electrophysiological methods. This approach has been used to identify differences in movement speed and variability between ET and healthy individuals (Deuschl et al, 2000; Köster et al, 2002; Schwartz et al, 1999; Trillenberg et al, 2006) and between PD and healthy individuals (Pfann et al, 2001; Vaillancourt et al, 2004). Identifying measures that differentiate PD from ET is highly desirable because the prognosis and early treatment options are different for each movement disorder
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