Transcranial Stimulation for Essential Tremor

The main purpose of this study is to see if transcranial magnetic stimulation (TMS) can be used to help study brain function in healthy people and in those with neurological diseases like essential tremor. This portion of the study is being done to establish the optimal methods for stimulating the brain to measure its responses.

Essential tremor (ET) is a movement disorder characterized by tremor of both hands, and often head and voice, affecting approximately 4.8-6.7 million individuals over the age of 40 in the United States alone. Hand tremor can limit basic activities of daily living like feeding, drinking, writing and dressing. While medications can be effective for tremor, they are often poorly tolerated due to their sedative or neuronal activity depressant properties. Surgical options such as deep brain stimulation of the ventral intermedius thalamus (Vim DBS) can be highly effective but its invasive nature limits its popularity. Noninvasive brain stimulation has demonstrated the ability to reduce tremor but precisely where to target brain stimulation to achieve the best results is currently unknown.

Repetitive transcranial magnetic stimulation (rTMS) enables noninvasive, selective and sustained modulation of specific neural networks, and can lead to clinical benefits in debilitating neurologic and psychiatric disorders, including medication-resistant depression, paresis following stroke or traumatic brain injury, Parkinson's disease, or dementia. There is also recent evidence that rTMS of the cerebellum can relieve hand tremor due to essential tremor. TMS uses electromagnetic induction to generate controlled currents in targeted brain structures that can be identified and defined using MRI-based neuronavigation. TMS is safe if appropriate guidelines are adhered to. To date, the impact of rTMS on ET has not been sufficiently established, but pilot studies offer promising results.

The investigators are testing whether MRI-guided neuronavigated cerebellar paired pulse TMS demonstrates abnormal physiologic measures in ET subjects compared to controls and whether there is reduction of tremor via cerebellar rTMS in patients with ET. The investigators plan to collect imaging, functional and neurophysiological assessments before and after the rTMS to identify the mechanistic underpinnings of rTMS-induced changes in tremor and cerebello-cortical inhibition.

Eligibility Criteria:
Inclusion Criteria for ET subjects:

1. Outpatients with essential tremor as diagnosed and confirmed by movement disorder specialist
2. Women of child-bearing potential must provide a negative pregnancy test at entry into the study
3. Stable doses of all medications for at least 14 days prior to study entry and for the duration of the study,
4. At least a 1cm amplitude tremor as judged by the screener using a ruler

Inclusion Criteria for Healthy Volunteers:

1. Healthy subjects without tremor and without significant neurologic disease suggestive of cerebellar ataxia or other neurodegenerative diseases
2. Ages 18-80

Exclusion Criteria:

1. Any unstable illness or concomitant medical condition that, in the investigator's opinion, precludes participation in this study, including disorders that may affect gait or balance (i.e., stroke, arthritis, etc).
2. Pregnancy or lactation.
3. Concurrent participation in another clinical study.
4. Dementia or other psychiatric illness that prevents the patient from giving informed consent (Montreal Cognitive Assessment Score score less than or equal to 21).
5. Legal incapacity or limited legal capacity.
6. Tremor derived from any cause other than essential tremor (Parkinson's disease, drug-induced, anxiety-induced) in the clinical assessment at screening
7. Currently taking lithium or amiodarone or any other drug judged to be contributing to tremor as judged by the investigator (may be a cause of tremor)
8. No medication is an absolute exclusion from TMS. Medications will be reviewed by the responsible MD and a decision about inclusion will be made based on the following:

   * The patient's past medical history, drug dose, history of recent medication changes or duration of treatment, and combination with other Central Nervous System active drugs.
   * The published TMS guidelines review of medications to be considered with TMS
9. History of seizures, diagnosis of epilepsy, history of abnormal (epileptiform) EEG, or family history of treatment resistant epilepsy with the exception of a single seizure of benign etiology (e.g. febrile seizures) in the judgement of the investigator
10. TMS and MRI-Specific exclusion criteria including:

    * Known metal in the head (such as a surgical aneurysm clip) or a history of prior neurosurgical procedures.
    * Ferromagnetic bioimplants activated by any electronic, mechanical or magnetic means, such as cochlear implants, pacemakers, medication pumps, vagal stimulators, deep brain stimulators, neurostimulators, biostimulators, or ventriculo-peritoneal shunts.
    * Subjects who have or might have bullet fragments or other shrapnel (veterans or workers exposed to metal in their work environment).
    * Subjects with metallic paint (e.g. color contact lenses, tattoos, metallic eyeliner)
    * Subjects expressing significant claustrophobia.