[Characterization and discrimination of kinetic tremor in Parkinson's disease]

Kinetic tremor recorded with a laser system during a compensatory tracking task of the index finger was analyzed in 21 patients with PD whose tremor amplitude was between low and moderate, and 30 control subjects. Nine characteristics quantifying the tracking task and tremor including mean tracking error, reaction time, peakedness, harmonicity, median frequency, proportional power in the 3-4 Hz, 4-6 Hz and 7-12 Hz ranges, and power at 0.25 Hz, were applied to the processed signal. The discriminating power of each characteristic was evaluated using differences between group means (p values), maximum percentage discrimination, and number of outliers in the patient group using z-score and 96.7(th) percentile of the control group. All nine characteristics showed significant differences between means of the two groups using Welch-modified t-tests for unequal variances. The most discriminating characteristics reflected differences in the frequency distribution of the movement and did not correlate highly with postural tremor amplitude nor with clinical ratings of tremor. Discrimination methods classified correctly up to 66.7 p.cent of the patients. Combining representative information about proportional power during posture and tracking gave a much higher discrimination (90 p.cent) with respect to the 96.7th percentile of the control group. These results suggest that by combining information coming from postural and kinetic tremors it is possible to isolate a specific aspect of PD symptomatology which could be used to reevaluate the classic distinction made between the akineto-rigid and tremulous forms of PD independently of tremor amplitude.