Essential tremor (ET) is the most common movement disorder. It most often affects the hands and can progress from barely visible tremors to severe motions that make the most ordinary tasks impossible. Medication helps about 50% of cases, but often loses effectiveness or leads to unwanted side effects. Because of this, researchers and clinicians are constantly trying to learn more about how tremors originate, and what can be done to stop them.
Intervening without medication
Since medication does not work for everyone, and is not always durable, neurologists seek ways to treat tremors at their source. This means interrupting the tremor circuit in the brain itself. To describe it simply, there are three brain components that offer potential for such intervention: the cerebellum (below the back portion of the brain), the thalamus (near the center of the brain), and the motor cortex (on the central side of each hemisphere’s surface). These separate areas are interconnected by pathways so they can communicate and function cooperatively to produce body movements.
Researchers believe overactive signals in the cerebellum may be the source of ET. These signals are funneled to the thalamus. There, a small “relay station” called the VIM nucleus intercepts them and directs them to the motor cortex. Once they leave the motor cortex, they travel to the body part where they are causing tremors. Apparently, the brain itself can’t self-correct these signals, either at their source (cerebellum) or anywhere along the circuit. This is where interrupting the circuit comes in.
A common example of a circuit that has more than one place to be interrupted is a plug-in lamp. If you want to turn off the light, you can either turn off the switch, unscrew the bulb, or unplug it from the wall. These are three different places that work together to produce light; interrupting any one of them will shut it down.
An ideal clinical intervention for ET that would not require medication would a) control the tremors, b) not cause damaging side effects, c) be long-lasting, and d) work for anyone who wanted it.
Today’s brain interventions for ET
Today, there are three neurosurgical methods that stop hand tremors without medication:
- MRI-guided Focused Ultrasound which immediately controls tremors by deadening the VIM nucleus (noninvasive)
- Deep Brain Stimulation which immediately controls tremors by electrically stimulating the VIM nucleus (invasive)
- Gamma Knife radiation which gradually controls tremors by deadening the VIM nucleus over time (noninvasive)
All three of these treatments target the center of the brain where the VIM nucleus lies in the thalamus. But what about the cerebellum or motor cortex?
Targeting other areas: a new noninvasive approach
For about two decades, researchers have been exploring ways to treat ET by noninvasively applying energy through the scalp and skull to the cerebellum or the motor cortex. It all began with trying to identify the components of the tremor circuit by testing the effects of either magnetic field energy or direct electrical stimulation on different brain areas.
The scientists found that by applying the energies at different frequencies for different periods of time, they could modulate the brain’s activity in the area being tested. Initially, this helped them pinpoint areas that functioned differently in individuals with ET vs. non-tremor individuals.
It was only natural that excitement grew over the therapeutic possibilities, including non-tremor applications for other neurological conditions such as clinical depression where, in fact, it is often effective. The term noninvasive brain stimulation was coined to refer to these approaches.
Clinical trials with human subjects have been – and continue to be – conducted to test magnetic and electrical stimulation of both the motor cortex and the cerebellum. So far, both types of energy appear to be safe and virtually free from side effects aside from minor scalp irritation or facial tingling, etc. However, if tremor control occurs, it is very temporary (minutes to weeks) and not to a great degree.
While the search continues…
Even though exploration into noninvasive brain stimulation has not yet brought it to a practical way to control tremors, it may yet prove useful for ET just as it has for depression.
In the meantime, patients who have had MRI-guided Focused Ultrasound (MRgFUS) for ET have regained quality of life along with control of their tremor. MRgFUS is a noninvasive outpatient procedure that gives immediate, lasting results. For more information, or to arrange a consultation, contact Sperling Neurosurgery Associates.