Electroclinical Correlates in Essential Tremor

Essential tremor (ET) is a neurological disorder that affects nearly 0.9% of the world's population, including 300,000 people in France alone. Patients who suffer from this condition usually present an upper limb tremor during voluntary motor activities but not at rest. The pharmacological treatments proposed for this condition are only effective in about 50% of patients, and this effectiveness is often only partial or observed at the cost of unacceptable side effects. Since the end of the 1980's, high-frequency deep brain stimulation (DBS) of the ventral-intermediate nuclei of the thalamus (VIM) has been proposed as an effective second-line treatment for severe forms of ET. However, some neuro-stimulated patients experience a recurrence of their tremor and may complain of an increase in pre-existing cerebellar ataxia. The mechanisms underlying these phenomena are still debated, but the fact that VIM stimulation is applied in a chronic and undifferentiated manner seems to play a determining role. One way to circumvent these phenomena could be to stimulate the VIM only during movement since the tremor in this condition is an action or postural tremor. This type of "closed-loop therapy" requires one or more intracerebral tremor biomarkers that can be reliably recognized and used to automatically trigger or modulate the intensity of VIM stimulation only when necessary. In a preliminary study in 10 patients, the investigators of Bordeaux university hospital were able to demonstrate the existence of potential intracerebral biomarkers of tremor under experimental conditions,in the immediate postoperative period (Guehl et al. 2022, submitted). The arrival on the market of the PERCEPT™ (new stimulator/recorder, Medtronic, Minneapolis, USA) now allows, in addition to treating patients with DBS, the recording of intracerebral activity at a distance from surgery, in a non-invasive way and in ecological condition at home. This study aim at recording the variations of thalamic oscillations, in ecological condition, during rest and movement, with and without deep brain stimulation. These measurements will be performed once a week during the 12 weeks of the late post-operative period (from 3 to 6 months), in order to ensure the reproducibility of the results. The signal processing and analysis will be performed in a blind manner to the patient's activity and stimulation condition.