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What is Essential Tremor?

Essential tremor (ET) is the most common movement disorder. It is a progressive, often inherited disorder that usually begins in later adulthood. Patients with ET typically experience tremors when the arms are held up (such as while reading a newspaper) and when the hands are being used for activities like eating, drinking or writing. The tremors also may affect the head and voice, but rarely affect the legs and can worsen with stress, fatigue and stimulant medications.

What causes essential tremor?

Essential tremor is thought to be caused by dysfunction of a network of brain regions that control movement. These regions include the cerebellum, red nucleus, globus pallidus, thalamus and cortex. Interruption of abnormal signals in this network may be why thalamic (ventral intermediate thalamus - VIM) stimulation using a surgically implanted device is often effective in treating essential tremor.

Treatment for Essential Tremor

Patients with significant functional impairment usually opt for some form of treatment. Less impaired patients may choose to forgo treatment all together. Some patients that aren’t functionally impaired desire treatment because their tremor is a significant source of embarrassment. Once a patient desires therapy, there are several options:

Non-Medical Therapy

In some patients, tremors can be reduced by weighting the limb, usually by applying wrist weights. In a small proportion of patients, this can dampen down the tremor enough to provide some relief or improve functioning.

Since anxiety and stress classically make the tremor worse, non-medical relaxation techniques and biofeedback can be effective in some patients.

Medications known to make tremors worse should be eliminated or minimized when possible. These can include lithium, several antipsychotics, valproic acid, corticosteroids, some anti-depressants and a class of drugs called adrenergic agonists. People with tremor also may benefit from avoiding dietary stimulants, such as caffeine. They should also be evaluated for hyperthyroidism, which can produce tremors that mimic ET.

Medication

Doctors and patients may decide to try medications when the degree of impairment or discomfort outweighs the side effects of treatment. The mainstay medications include beta adrenergic blockers ("beta blockers"), such as propranolol (Inderal), and the anti-seizure medication primidone (Mysoline).

  • Primidone – the effectiveness of this drug in treating ET was first noted in a patient being treated for epilepsy. Primidone has been shown to be effective in several controlled trials, and is often the first medication prescribed for patients with ET. Some patients may experience a “first dose phenomenon” where they have transient feelings of unsteadiness, dizziness and nausea at the beginning stages of treatment. This is usually short-lived. Sedation is another common side effect and can be reduced by following a slowly escalating dose schedule. Most patients are able to tolerate the side effects, and studies have shown 60-100 percent of patients respond positively.
     
  • Propranolol – This beta blocker is effective in 40-50 percent of patients and is less useful in reducing head and voice tremor. It should not be used in patients with asthma, emphysema, congestive heart failure or heart block and should be used with caution in people with diabetes who are on insulin. These drugs may reduce exercise tolerance, lower blood pressure or heart rate, exacerbate depression and cause impotence. Other adrenergic blockers with fewer side effects include atenolol, nadolol, metoprolol and timolol.
     
    If both primidone and propranolol are not effective alone, combinations of both may provide relief in selected patients.
     
  • Miscellaneous medicationsBenzodiazepines, especially clonazepam, have long been used in the treatment of ET. Side effects of this class of medication include sedation and a risk of dependence. Other medications, including gabapentin, topiramate and methazolamide, may be prescribed for refractory patients who have not obtained significant relief or who are unable to tolerate the more common therapies.
     
  • Botulinum toxin injections – This treatment method is typically recommended for those with severe head tremor, or, more rarely, upper limb tremor. Although head tremor rarely leads to impairment of functional abilities, the embarrassment may cause patients to feel socially isolated. Several studies have shown that botulinum toxin injections may significantly help head and voice tremors. Hand tremors also may be reduced with botulinum toxin, but the injections are most effective when only a few muscles are involved in a simple rhythmic motion, and this is not the case with all hand tremors.

Surgery

When patients do not achieve satisfactory control of their tremor with non-medical or medical therapies and there is significant functional impairment, neuromodulation and other advanced therapies may be considered.

Video 1
Patient’s essential tremor stimulator turned off

Video 2
Patient’s essential tremor stimulator turned on

 

Surgical Lesion – Placing a surgical lesion in an area of the brain called the ventral intermediate thalamus (Vim) has been used to treat essential tremor for decades. Between 80 and 90 percent of patients have sustained benefit from this type of treatment. This procedure does not require leaving any permanent hardware in the body. Attempts to control tremor on both sides of the body using this procedure have led to an increased risk of developing speech problems, thus limiting its usefulness.

Deep Brain Stimulation (DBS) – A safer option for bilateral treatment is deep brain stimulation (DBS), which stimulates the brain at high frequencies. An advantage of DBS is that it is reversible and controllable. This allows physicians to adjust the stimulator for maximum benefit and fewest side effects. One disadvantage is that it requires surgical implantation of permanent hardware.

Preoperative Assessment
All patients considering DBS to treat their symptoms are evaluated by a neurologist on our team. During this evaluation, the physician decides whether the medications the patient is taking are appropriate and optimized, or whether less invasive treatments are available as alternatives. A neuropsychological evaluation is typically performed to assess for cognitive strengths and weaknesses that may affect surgical candidacy.  Medical clearance through the patient's internist may be required prior to scheduling surgery. A neurosurgeon from our team then evaluates the risks and benefits of the surgery in the context of each patient’s needs. 

The Implanted System
The system consists of one or two electrode(s) that goes/go into the brain, a connecting cable, and the "neurostimulator" which contains electronic circuitry as well as a battery. The entire system is implanted completely under the skin. The physician and patient each have a programmer that can communicate with the device through the skin.

Programming of the Deep Brain Stimulator

Immediately following the surgery, there may be some benefit without the stimulator even being turned on. This is thought to be due to swelling around the tip of the implanted electrode. This effect can diminish over the following weeks to months.

Usually, the initial programming is done three to four weeks after the surgery. During the first session, which lasts a few hours, the doctor programs various parameters of stimulation (voltage, frequency of stimulator and which of the four electrodes are used). This process requires continuous feedback from the patient to determine if there are any side effects and to determine the best settings for tremor relief.
 
Patients typically return a few times over the next several months until the stimulator is programmed optimally. While programming may require more than one visit, most patients (80-90%) get very significant reduction in their tremor by the end of the process.

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