Hand rhythmic tapping and timing in Parkinson's disease

Background. Dysrhythmia is one of the features frequently associated with the motor disturbance in Parkinson's disease (PD). The mechanism responsible for this phenomenon is not known. Objectives. To assess the rhythmic movements of the hand in PD patients in general and in parkinsonian subtypes. Methods. Fifty-one PD patients (32 males) with mean age 66.3±9.1 years (6.6 years of symptoms) and 36 healthy controls (age 64.9±13.2, range 40-85) were studied. Subjects were asked to tap with their dominant or less affected arm on a digitized switch board at their most comfortable pace (16 s), fastest tapping speed (12 s), and at different frequencies provided by a metronome. The mean rhythm and the tap-to-tap variation were compared. Performance of the PD patients and control subjects were compared, as there were different subtypes of PD patients. Patients were subclassified into: tremor predominant (TP) (14 patients), freezing predominant (FP) (11 patients), akinetic-rigid (AR) (12 patients) and an unclassified group (UC) (14 patients). Results. There was no significance difference between patients and controls in the self-chosen, most comfortable tapping rate or in the tap-to-tap variation of the self-paced task. PD patients tapped at a significantly slower rate than controls when asked to tap at their fastest rate (4.39±1.32 vs. 5.14±1.31 Hz; p<0.01). This difference was the result of an especially slow performance of the TP and AR subgroups (3.85±1.20 and 3.88±1.46, respectively; p<0.01, compared to the control group). TP was the only subgroup to show an increased tap-to-tap variation at their fastest tapping rate compared to the control group (0.070±0.057 vs. 0.029±0.025 s, respectively, p<0.05). The TP subgroup also showed hastening when they followed an externally given rhythm of 2.5 Hz and they tapped at 2.73±0.36 Hz (p<0.05). Conclusions. Externally driven and self-paced tapping are preserved in patients with PD, when examined at their best 'on' state. The tremor predominant subgroup seems to have specific pacing disturbances.