[Differentiation of parkinsonian and essential tremor using electrophysiological methods]

Tremor is one of the most common movement disorders. Different tremors are induced by central and/or peripheral oscillators. The motor cortex plays a significant role in the generation of parkinsonian tremor but its function in essential tremor is not clear. We examined the effect of motor cortex activation on parkinsonian and essential tremor during movement of the contralateral hand. Our aim was to study the role of interhemispheric motor connections in genesis of different tremors.

We recorded the tremor of nine Parkinson patients and seven patients suffering from essential tremor using accelerometry. After Fast Fourier-transformation of digitized tremor signal we measured the power changes at the peak frequency after flash triggered movement (FM) and self-paced movement (SPM). For control we used flash signal without movement.

Peak frequency of parkinsonian and essential tremor was not different. The power decrease of parkinsonian tremor was significant during flash triggered and self-paced movement compared to the effect of flash (p(Flash-FM)=0.0008; p(Flash-SPM)=0.002), changes during the different movement protocols were not different (p(FM-SPM)=0.33). During self-paced movement parkinsonian tremor became significantly smaller than essential tremor (p<0.05). The effect of movement was not significant on the power of essential tremor (p=0.42), probably due to high standard deviation of individual data.

Voluntary movement of the contralateral hand decreases parkinsonian tremor suggesting that its generator can be inhibited via the activation of the motor cortex. The diverse reaction of essential tremor may reflect various connections between its generator system and the motor areas, therefore it is not a separate disease entity.