A method to assess hand motor blocks in Parkinson's disease with digitizing tablet

The non-volitional sudden discontinuation of motor activity, called motor block (MB) or freezing is most commonly associated with Parkinson's disease (PD). MB extends beyond the classical manifestations of PD: akinezia, bradykinezia, rigidity, tremor, and postural instability. MB has been observed and quantified in internally cued repetitive movements such as gait, speech, handwriting, and manual tapping tasks as a distinct feature of PD. We present a simple measurement system for objective evaluation of MB during point-to-point hand movements in patients with PD. Hand trajectories were evaluated in eight PD patients based on values obtained from a digitizing tablet (DT) score. 50 trials per day were recorded in seven consecutive working days. Subjects were instructed to consciously prepare and self-initiate movements between arbitrarily fixed starting and target points without lifting a wireless magnetic mouse. MB was identified as the time interval during movement with no change in coordinates. We analyzed three kinematic parameters: duration, start and number of MBs. If MBs were documented, the DT score was 1, if not, 0. Results were then compared with the ratings of the question in motor section related to freezing of hands from the Unified Parkinson's Disease Rating Scale (UPDRS). For all patients, DT score was in agreement with the UPDRS. Present results indicate that DT is useful for assessing MBs during volitional planar hand movement. This low-cost instrument may be included in a clinical test battery because of short testing time and trouble-free preparation of patient.