Essential tremor (ET) is the most common movement disorder. The majority of ET cases affect the hands, interfering with normal tasks like dressing, eating, drinking , typing, etc. Also, it is visible to others who are not familiar with ET, leading to negative judgments and embarrassment.
While there is no cure for ET, treatments and lifestyle changes that can make life easier. However, ET usually worsens over time. Even cases that responded to medication initially may become more severe than drugs can manage. After months or years of increasing helplessness, the longing for a permanent solution becomes intense. Thankfully, there are two neurosurgical procedures that offer relief: Focused Ultrasound (FUS) and Deep Brain Stimulation (DBS).
Tremor signals in the brain
ET is believed to originate in a part of the brain called the cerebellum. We don’t yet know what triggers the abnormal signals that lead to tremors in the body. We do know that these signals are transmitted along what is called the tremor pathway. When abnormal signals leave the cerebellum they travel into a central part of the brain called the thalamus. Within the thalamus, there are several small centers or nuclei. One of them, the VIM nucleus, is a key player in forwarding tremor messages.
Imagine a large city served by a major railroad terminal. Trains arrive from many directions, and leave by many different tracks. With the push of a button, switching stations direct them to one track or another with. Both the thalamus and the VIM nucleus are similar to a switching station since they forward tremor signals to other parts of the brain where they are “assigned” to one part of the body or another, resulting in visible tremors. Therefore, neurosurgical treatments for ET are aimed blocking abnormal signals that reach the thalamus and the VIM nucleus within it.
Treating the thalamus and the VIM nucleus
Intervening in the thalamus to block tremors can be done either by ablating (destroying) part of it or by electrically stimulating it. Ablating the thalamus is called thalamotomy. Implanting electrodes to stimulate it is called deep brain stimulation (DBS). Until the last few years thalamotomy was an invasive procedure that involved inserting a probe through a hole in the stall to destroy part of the thalamus with extreme cold or extreme heat. Now however, there is a new noninvasive thalamotomy procedure called focused ultrasound (FUS). Persons with ET desire permanent relief now have a choice of two treatments: FUS or DBS. Which is better?
A new study compares FUS and DBS
A 2019 study by Harary, et al.i (Harvard Medical School) offers a comparison of unilateral thalamotomy using FUS vs. DBS. (“Unilateral” means treating only the side of the thalamus that controls the dominant hand; both procedures can be done bilaterally [both sides] but unilateral has fewer complications.) In the published paper the authors compared two clinical trials on FUS and DBS for the following:
- Tremor score (degree of tremor improvement)
- Adverse events (side effects)
- Quality of life.
The authors report that both treatments provide comparable tremor improvement and quality of life at one year after treatment. The major difference concerns side effects. In the FUS group, there were treatment-related effects such as facial tingling or speech difficulties that took weeks or months to resolve. In the DBS group, there were higher rates of complications related to surgery or hardware as well as a greater risk of bleeding in the brain. This table sums up the key differences:
|Noninvasive – outpatient treatment under MRI guidance using beams of ultrasound through the skull to ablate the VIM nucleus||Invasive – 2 inpatient surgeries ( implant electrodes through a hole drilled in the skull, and implant a battery pack in the chest connected with wires through the neck to the electrodes in the brain)|
|Low risk of side effects that can include facial tingling, speech difficulties, and balance issues. If these occur, they tend to resolve within a couple of months.||Low risk of side effects that can include infection, hardware issues, speech difficulties, and very low risk of bleeding in the brain.|
|Follow-up studies at three years suggest durable tremor control||Long-term studies suggest durable tremor control which can be adjusted if tremors become worse.|
|No hardware in the body||Electrodes can move out of place over time, and batteries need to be replaced surgically.|
What the Harary paper indicates is that there are two great options for durable tremor control. People with ET don’t have to ask, “Which procedure is better?” because the outcomes are comparable. Instead, they should ask, “Which procedure is better for ME?” For more information on how MRI-guided FUS might be the right treatment for you or a loved one, visit our website for more information on the treatment, and how to contact us.
iHarary M, Segar DJ, Hayes MT, Cosgrove GR. Unilateral Thalamic Deep Brain Stimulation vs. Focused Ultrasound Thalamotomy for Essential Tremor. World Neurosurg. 2019 Feb 19.