[A case presenting with both features of essential tremor and Parkinson tremor].

A 78-year-old woman had postural and action tremor in hands since age of late 20's, though without much difficulty in daily living. Since age 76, she has had an increasing difficulty in walking and postural balance, with some worsening of hand shaking as well. She also noted to have head shaking, involuntary movements in the mouth, and some difficulty in swallowing. Reportedly both of her parents and her brother had hand tremor. Neurologically she had resting, postural and action tremors in hands more on the left. She also had marked rigidity in the neck and moderate cogwheel rigidity in all limbs more on the left, moderate bradykinesia, markedly stooped posture with relatively wide base, slow and small-paced gait, and poor postural balance more posteriorly. Thus, it is most likely that the present case suffered from essential tremor and later developed Parkinson disease. Power spectrum analyses of surface electromyogram and accelerometer showed the peaks at 4.3 Hz for the resting tremor, and 3.1 and 5.2 Hz for the postural tremor. Furthermore, significant EEG-EMG coherence was seen at the peaks of 4.3 and 5.2 Hz, suggesting possible involvement of sensori-motor cortex for generation of both tremors. When the postural tremor was loaded with 500 g weight, the peak of power spectrum and EEG-EMG coherence showed the broader pattern with the maximal peak at 4.3 Hz, exactly the same frequency as that of the resting tremor. These findings may be explained by postulating that the 4.3 Hz peak of the resting tremor became apparent by loading because 5.2 Hz peak of the postural tremor was suppressed by the loading. The peak of the postural tremor at 3.1 Hz which was not detected by EEG-EMG coherence suggested that the tremor for 3.1 Hz was not involved to sensori-motor cortex for generation.