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BACKGROUND: Pharmacologic interventions (e.g., beta blockers) and thalamic lesions have failed to alter the pathophysiology of essential tremor (ET) beyond a reduction in tremor amplitude. Deep brain stimulation (DBS) of the ventral intermediate (VIM) nucleus of the thalamus successfully reduces tremor rating scores. It is unknown how VIM DBS alters the pathophysiologic characteristics of ET. OBJECTIVE: To determine the effects of VIM DBS on the neurophysiologic characteristics of ET. METHODS: Hand tremor and EMG activity of forearm extensor and flexor muscles were recorded in six patients with ET ON-DBS and OFF-DBS and from six age- and sex-matched control subjects. Hand tremor was assessed across different inertial loads. The amplitude, frequency, regularity, and tremor-EMG coherence were analyzed. RESULTS: VIM DBS reduced the amplitude, increased the frequency, decreased the regularity, and reduced the 1 to 8 Hz tremor-EMG coherence of ET. ON-DBS, patients with ET had greater tremor amplitude, lower frequency, more regularity, and greater tremor-EMG coherence compared to control subjects. CONCLUSIONS: Whereas pharmacologic and thalamic lesions have previously failed to change characteristics of ET beyond amplitude reduction, VIM DBS modified multiple features of ET. The changes in ET after VIM DBS provide strong evidence for clinical efficacy.
Vaillancourt et al. (Tue,) studied this question.