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INTRODUCTION: An algorithm to study hand movements in patients with Parkinson's disease (PD) who experience temporary, involuntary inability to move a hand have been developed. In literature, this rather engimatic phenomenon has been described in gait, speech, handwriting and tapping, and noted as motor blocks (MB) or freezing episodes. Freezing refers to transient periods in which the voluntary motor activity being attempted by an individual is paused. It is a sudden, unplanned state of immobility that appears to arise from deficits in initiating or simultaneously and sequentially executing movements, in correcting inappropriate movements or in planning movements. The clinical evaluation of motor blocks is difficult because of a variability both within and between individuals and relationship of blocks to time of drug ingestion. In literature the terms freezing, motor block or motor freezing are used in parallel. AIM: In clinical settings classical manifestations of Parkinson's Disease (akinesia, bradykinesia, rigidity, tremor, axial motor performance and postural instability) are typically evaluated. Recently, in literature, new computerized methods are suggested for their objective assessment. We propose monitoring of motor blocks during hand movements to be integrated. For this purpose we have developed a simple method that comprises PC computer, digitizing board and custom made software. Movement analysis is "off line", and the result is the data that describe the number, duration and onset of motor blocks. METHOD: Hand trajectories are assessed during simple volitional self paced point-to-point planar hand movement by cordless magnetic mouse on a digitizing board (Drawing board III, 305 x 457 mm, GTCO Cal Comp Inc), Fig. 1. Testing included 8 Parkinsonian patients and 8 normal healthy controls, age matched, with unknown neurologic motor or sensory disorders, Table 1. Three kinematic indicators of motor blocks: 1) duration (MBT%); 2) onset (t%); and 3) number (N) of MB episodes, allow identification and quantification of motor blocks. Duration of motor blocks (MBT) is defined as the time sequence when (x,y) coordinates do not change their values and is expressed in percentage from the whole movement duration MBT% = MBT/T (%). If during some movements more than one motor block occurs (N > 1) then this movement is decomposed. The whole movement motor block (mbt) is the sum of all motor blocks MBT; during the same movement and expressed in percentage from the whole movement duration mbt% = mbt/T (%). The onset of motor block (t) is determined with the beginning of motor block and expressed in percentage from the whole movement duration: t% = t/T (%). After the determination of kinematic indicators of motor blocks (MBT, N, t) for healthy controls, their mean values are calculated. Statistical package ANOVA is applied to determine statistical significance of the difference between PD patients and mean values from age matched control healthy group. PD patients are then classified into two groups: one group consisting of PD patients with motor blocks and the other without motor blocks, similar to healthy controls. RESULTS: Acquired movements are processed and analyzed. Fig. 2 is an example of hand trajectories. Time course of (x, y) coordinates indicates motor block appearance, Fig. 3. Detailed presentation of kinematic indicators of motor block (MBT, N, t) is in Fig. 4. Intra-subject variability of these parameters is presented in Figs 5, 6 and 7 for patient #3. The results for N show that 45% of all patients #3 movements had none motor blocks (N = 0); 20% had N = 1; 15% had N = 2; 11.5% had N = 3; 5.7% had N = 4; 0.3% had N = 5; 0.7% had N = 6; 0.3% had N = 7 and 1% had N = 8 motor blocks. The results for t% show that 3% of all patients' #3 blocks started at first quarter, 17% started in the second, 36% in the third, and 44% in the last quarter of movement. The results for MBT% show that 14.5% of all movements had MBT% in the range 0-5%; 56% had MBT% 5-10%; 22% had MBT% 10-15%; 5.5% had MBT% 15-20% and 2% had MBT% 20-25%. No block lasted more than 25% from the whole movement duration. Table 2 is the summary of mean variability for kinematic indicators of motor block (N, mbt%, t%) and for the movement duration T during a 7 day-testing of patients #3. The analysis of calculated data for eight tested PD patients revealed a significant difference (p < 0.01) between healthy controls and three PD patients; data on five PD patients were not significantly different (ns). This method clustered 3 PD patients in the group that experience motor blocks, while the rest were in the group without their significant occurrence. DISCUSSION: This algorithm is an additional instrument in classical evaluation of PD patients during their clinical evaluation and treatment. It provides to clinician a rapid feedback on the changes of voluntary hand movements in everyday progress of illness. Furthermore, this method could be of assistance for developing strategies to overcome motor blocks in arm movements at their beginning, as well as for the feedback of the success of drug therapy.