What is essential tremor?

Essential tremor refers to the involuntary, abnormal, rhythmic, oscillating movement  affecting a part of the body, produced by the alternating or simultaneous contraction of agonist and antagonist muscles. Although there are many types of tremors (over 20), essential tremor is the most common of all. This is a disorder of the nervous system that causes involuntary, rhythmic movements. Although it can affect almost any part of the body, tremor occurs most often in the hands, especially when doing simple tasks, such as drinking from a glass or tying shoelaces.

In general, it is not serious, but it tends to get worse over time and can be severe in some people. The intensity of the tremor is accentuated in situations of emotional tension, fatigue, ingestion of stimulants (caffeine) or when feeling observed. It improves with alcohol intake and disappears during sleep.   

One in 20 people over the age of 40, and 1 in 5 people over the age of 65, may have essential tremor. Essential tremor can appear for the first time at any age, although the average age of onset is between 35-45 years. The worldwide prevalence of essential tremor is estimated to range from 0.4 to 6%, increasing with age. It affects both sexes equally.

Causes

Essential tremor can occur sporadically or in families. A family history of tremor is found in 60% of patients. In those cases where there is no genetic origin, the causes are not clear. The genetics of ET appear to be varied, with the involvement of several genes as a risk factor for the disease.

Symptoms and diagnosis of essential tremor

SYMPTOMS

Essential tremor is characterized by rhythmic tremor that occurs during voluntary movements (kinetic tremor) or when maintaining a position against gravity (postural tremor). Tremor can manifest itself in the following ways:

  • Rhythmic trembling of the hands, arms legs or trunk
  • Tremulous voice
  • Difficulty in writing or drawing
  • Difficulty in holding and controlling utensils, such as a spoon.

DIAGNOSIS

Essential tremor is often misdiagnosed. The disease must be identified by clinical diagnosis, based on the criteria created by the Movement Disorder Society (MDS), and must comply with all of the criteria, both fundamental and exclusionary.

Although the diagnosis is made by physical examination of the patient, in order to rule out some possible causes of this tremor, it is often necessary to perform a brain MRI, other neuroimaging, and other neurophysiological tests.

Treatment of essential tremor

Treatment will depend on the severity of the tremor, the part of the body where it occurs, the patient's occupation, and how it affects their quality of life. Pharmacotherapy of essential tremor is limited and there is no one drug that benefits all patients. When pharmacological treatment does not adequately control tremor, surgical treatment may be chosen.   

There are several modes of surgical treatment, but we will focus on describing the most widely used today.

Surgical ablation

This type of surgery consists of producing an ablation or controlled injury in a selected small part of the brain. This treatment modality can be carried out interchangeably by three different methods and each of them constitutes a treatment technique in itself: radiofrequency thermal ablation, ionizing radiation injury (radiosurgery), and thermal ablation when administering a high dose of Ultrasonic energy using magnetic resonance-guided focal ultrasound. 

Deep brain stimulation (DBS)

This is the most widely used treatment modality worldwide today. It consists of high frequency stimulation in a small part of the brain. Through electrical impulses, the part of the brain that is abnormally overactive is inhibited or modulated – the part responsible for the symptoms of the disease. To do this requires implanting brain electrodes and a small neurostimulator similar to a cardiac pacemaker in the body. Once implanted, your doctor can adjust device settings and stimulation levels using an external programming device. In this surgical technique, electrical stimulation is performed on the dentato-rubro-thalamic tracts (DRT) and fundamentally in one of the following two regions: at the level of the nucleus ventralis intemedialis (Vim) and at the level of the posterior suthalamic area (PSA). Both regions have shown to be effective, although there are currently studies trying to define possible differences between the two targets.

This surgery is carried out following the methodology that we describe here.

A stereotactic guide or crown is first placed on the patient's head. The radiological location of the surgical target is determined with neuroimaging fusion (CT/MRI), combining anatomical images and diffusion tensors (DTI tractography). Once this is done, the intracerebral trajectories are simulated by the computer with the support of very powerful surgical programs or software. 

The patient receives local anesthesia/sedation, and the highly accurate image-guided surgical technique is performed using the help of various neural electrical records and micro-stimulation to identify the electrophysiological location of the surgical target. 

The electrodes are immediately implanted in the selected structure. A small, rechargeable neurostimulator is also implanted in another part of the body (infraclavicular region or abdomen), which is connected to the electrodes to stimulate these brain structures. This system implanted in the patient is controlled by the doctor in each hospital visit in a non-invasive way, through a programming device that uses 3D graphics to allow the stimulation parameters to be easily adjusted, including the directional stimulation that helps increase the efficiency and safety.

Who are the doctors at Instituto Clavel who treat essential tremor?

Dr. Clavel
Dr. Català

Sources

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