The impact of ventrolateral thalamotomy on high-frequency components of tremor.
OBJECTIVE
The present study assessed the impact of ventrolateral (VL) thalamotomy on the high-frequency components of tremor in patients with Parkinson's disease (PD).


METHODS
Tremor was recorded prior to, and 7 days post-surgery using a laser displacement sensor. In addition, tremor was recorded in 10 age-matched patients with PD showing low amplitude tremor (named PD controls) and in 10 age-matched control subjects. Tremor recordings in patients were performed after a 12h withdrawal from anti-Parkinsonian drugs. Tremor characteristics such as amplitude, median power frequency (MPF) and power dispersion (a measure of concentration of power in the frequency domain) were assessed for all groups (i.e. controls, PD controls, pre-surgery and post-surgery).


RESULTS
All tremor characteristics were similar between controls and PD controls. Tremor amplitude was significantly reduced post-surgery, to become statistically similar to that of controls and PD controls. However, MPF and power dispersion remained lower post-surgery, indicating that although there was normalization of tremor amplitude, tremor showed systematically slower oscillations after the surgical procedure. In order to eliminate amplitude as a possible confounding factor, epochs of post-surgical tremor (5s in duration) were paired for equal amplitude with 5s tremor epochs from matched controls. Results show once again that MPF and power dispersion were lower post-surgery compared to controls. In addition, when amplitude of power was compared within specific frequency bands (0-3.5, 3.5-7.5, 7.5-12.5, 12.5-16.5, 16.5-30 and 30-45), power regained normal values at frequencies below 7.5 Hz. Power within higher frequency bands was systematically lower, indicating that the surgical procedure had an impact on high-frequency components of tremor.


CONCLUSIONS
Results from the present study showed that VL thalamotomy reduced tremor amplitude by selectively targeting centrally driven components of PD tremor. The high-frequency component of physiological tremor failed to emerge after amplitude normalization.


CONCLUSIONS
The thalamus should then be considered as an important component of the generation and/or propagation of high-frequency components of physiological tremor.
Duval
Christian
C
Faculty of Applied Health Science, Brock University, 500 Glenridge Avenue, St Catharines, Ont., Canada H2S 3A1. cduval@brocku.ca
Strafella
Antonio P
AP
Sadikot
Abbas F
AF
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001931:Brain Mapping; D016022:Case-Control Studies; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications / Q000601:surgery; D011612:Psychosurgery / Q000379:methods*; D012044:Regression Analysis; D013788:Thalamus / Q000503:physiopathology / Q000601:surgery*; D016896:Treatment Outcome; D014202:Tremor / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*