Modulation of primary orthostatic tremor by magnetic stimulation over the motor cortex
a Department of Neurology
and University Department of Medicine, Royal Adelaide Hospital,
Adelaide, Australia, b Australian Neuromuscular Research
Institute, Queen Elizabeth II Medical centre, Nedlands, Western
Australia, c Department of Neurology, Chang Gung Memorial Hospital, Taipei,
Taiwan
Correspondence to: Professor P D Thompson, Department of Neurology and University Department of Medicine, Royal Adelaide Hospital, North Terrace, Adelaide SA 5000, Australia.
Received 16 December 1996 and in revised form 2 July 1997;
Accepted 9 July 1997
OBJECTIVES
To study the role of corticomotor
neuronal pathways in primary orthostatic tremor.
METHODSTranscranial magnetic stimuli at an
intensity 10% above the resting motor threshold were delivered over
the leg motor cortex in two patients with primary orthostatic tremor
while standing still. Electromyographic responses in both tibialis
anterior muscles were recorded after 20 stimuli given randomly at
intervals of 120 to 180 seconds. Differences between predicted
and actual times of occurrence of tremor bursts after the stimuli were
used to calculate a resetting index, with a value of 0 representing no resetting and a value of 1 representing complete resetting.
RESULTSTranscranial magnetic stimulation evoked
EMG responses in both tibialis anterior muscles, followed by transient
suppression of tremor before reappearance of rhythmic EMG activity.
Analysis of the timing of tremor bursts from EMG recordings before and after the magnetic stimuli disclosed that the phase of orthostatic tremor could be reset by brain stimulation (mean resetting indices 0.93 and 0.82).
CONCLUSIONThe results suggest that a central
oscillator, involving the motor cortex, has a crucial role in either
the generation or modulation of orthostatic tremor.
© 1998 by Journal of Neurology, Neurosurgery, and Psychiatry
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