Re-emergent Tremor in Parkinson's Disease: The Role of the Motor Cortex.
BACKGROUND
Parkinson's disease patients may show a tremor that appears after a variable delay while the arms are kept outstretched (re-emergent tremor). The objectives of this study were to investigate re-emergent tremor pathophysiology by studying the role of the primary motor cortex in this tremor and making a comparison with rest tremor.


METHODS
We enrolled 10 Parkinson's disease patients with both re-emergent and rest tremor. Tremor was assessed by spectral analysis, corticomuscular coherence and tremor-resetting produced by transcranial magnetic stimulation over the primary motor cortex. We also recorded transcranial magnetic stimulation-evoked potentials generated by motor cortex stimulation during rest tremor, tremor suppression during wrist extension, and re-emergent tremor. Spectral analysis, corticomuscular coherence, and tremor resetting were compared between re-emergent tremor and rest tremor.


RESULTS
Re-emergent tremor showed significant corticomuscular coherence, causal relation between motor cortex activity and tremor muscle and tremor resetting. The P60 component of transcranial magnetic stimulation-evoked potentials reduced in amplitude during tremor suppression, recovered before re-emergent tremor, was facilitated at re-emergent tremor onset, and returned to values similar to those of rest tremor during re-emergent tremor. Compared with rest tremor, re-emergent tremor showed similar corticomuscular coherence and tremor resetting, but slightly higher frequency.


CONCLUSIONS
Re-emergent tremor is causally related with the activity of the primary motor cortex, which is likely a convergence node in the network that generates re-emergent tremor. Re-emergent tremor and rest tremor share common pathophysiological mechanisms in which the motor cortex plays a crucial role. © 2020 International Parkinson and Movement Disorder Society.
['Leodori|Giorgio|G|', 'Belvisi|Daniele|D|', 'De Bartolo|Maria I|MI|', 'Fabbrini|Andrea|A|', 'Costanzo|Matteo|M|', 'Vial|Felipe|F|', 'Conte|Antonella|A|', 'Hallett|Mark|M|0000-0002-3180-6811', 'Berardelli|Alfredo|A|']
D006801:Humans D009044:Motor Cortex D010300:Parkinson Disease D050781:Transcranial Magnetic Stimulation D014202:Tremor D014953:Wrist
tremor Parkinson's disease motor cortex TMS-EEG clinical neurophysiology