Judgment of disability stages in Parkinson disease patients due to pathological tremor of index finger.

The purpose of this study is to investigate the disability stages of Parkinson disease (PD) patients by wave analysis of parkinsonian pathological tremor. Physiological tremor and pathological tremor for the index finger are detected by accelerator sensor. The power spectrum is calculated by an auto-regressive model (AR model). The peak frequency and the peak power of the tremor for the index finger are evaluated under two conditions: (1) maintaining the index finger in a horizontal position using visual feedback with or without a weight load of 50 g, in which tremor is referred to as postural tremor, (2) resting the index finger with eyes closed, in which the tremor is referred to as resting tremor. The physiological tremor and the pathological tremor for the finger are characterized by two peak frequency components in which the first peak frequency component is 8-12 Hz, and the second is 20-25 Hz under the two conditions stated above. The peak frequency and the peak power for the PD patients at the two peak frequency components show the characteristics for the disability level of the PD patients. The first peak power especially around 8-12 Hz in the postural tremor without and with the weight load significantly increases as the disability stage determined by the Hoehn-Yahr method worsens, and there is significant difference of the peak powers for the stages. These results suggest that the first peak power around 8-12 Hz for the postural tremor without and with the weight load is a useful index to judge PD disability stage. It is found that postural tremor without and with the weight load gives the significant peak frequency and peak power compared with those for normal persons. It is pointed out that the first peak frequency component of 8-12 Hz originates from the central nervous system, and the first peak power reflects the degrees of disorder in the central nervous system, since PD is caused by the functional lowering of the central nervous system.