Distinguishing the tremor of Parkinson's disease from essential tremor: Finger displacement

Abraham Lieberman, Barrow Neurological Institute
Rohit Dhall, Barrow Neurological Institute
Sara Dhanani, Barrow Neurological Institute
Naomi Salins, Barrow Neurological Institute
Arshia Sadreddin, Barrow Neurological Institute
Guillermo Moguel-Cobos, Barrow Neurological Institute
Di Pan, Arizona State University
Anthony Santiago, Barrow Neurological Institute
George Prigatano, Barrow Neurological Institute
Narayanan Krishnamurthi, Barrow Neurological Institute
Alexander Troster, Barrow Neurological Institute


Although, the tremor of Parkinson's disease (PD) usually, but not always, differs from essential tremor (ET), there is no simple bedside test to distinguish PD from ET. We believe we have made such an observation. We studied 50 consecutive tremor-dominant PD patients (mean age: 63.4 years; mean disease duration: 4.9 years) and 35 consecutive ET patients (mean age: 64.1 years; mean disease duration: 12.5 years). Among PD patients, 31 had a bilateral tremor and among ET patients, 29 patients had a bilateral tremor. Patients sat opposite the examiner and pointed both index fingers at the examiner's index fingers. Then they closed their eyes. Within 15 s, one or rarely both of the patient's index fingers moved, was displaced, either upward or laterally. Finger displacement occurred only with bilateral simultaneous pointing with the patient's eyes closed. All the tremor-dominant PD patients exhibited displacement of an index finger. In 46 patients, it occurred on the side of dominant tremor, in 4, it occurred bilaterally. In 31 of 35 ET patients, no displacement occurred. In 4 of 35 ET patients, it occurred unilaterally on the side of dominant tremor. Odds ratio of distinguishing PD from ET: 89.62 at 95% confidence limits (5.31-1513.4), p = 0. 0018. Sensitivity 100% (0.91-1), specificity 89% (0.72-0.96). Finger displacement can distinguish the tremor of PD from ET. The unilateral movement with eyes closed suggests the tremor of PD unlike ET may impact circuits involving the parietal and supplementary motor cortices. © 2014 Informa Healthcare USA, Inc.