Don’t Be Afraid of “Irreversible” Focused Ultrasound

We encounter it a lot. A person with essential tremor (ET) comes in for a consultation. He/she has been on primidone and/or propranolol for years. The side effects (fogginess, fatigue, etc.) have become unacceptable. Simple tasks are virtually impossible. In short, life sucks. This person now wants a permanent, non-drug solution. They’ve already consulted a neurosurgeon at an eminent academic center about Deep Brain Stimulation (DBS) but they are worried about such an invasive surgery.

They are very drawn to the Neuravive treatment we offer, which uses noninvasive MRI-guided Focused Ultrasound (MRgFUS or FUS). However, when they asked the neurosurgeon about it, they were told, “Well, unlike DBS, it’s irreversible.” Suddenly, it sounds scary. An irreversible procedure in the brain – will it change or harm them in some unforeseen way? Will it turn out to be a terrible trade-off, returning normal use to a hand in exchange for losing something else?

Permanent physical changes

People naturally take time to ponder before deciding to alter their body in a permanent way. Of course, some irreversible medical procedures like removing an infected appendix or cancerous organ are the result of a life-threatening situation.

However, there are nonemergency interventions that are irreversible (or difficult to reverse) but that deliver a greater good. Things like a vasectomy (men) or tubal ligation (women) for responsible family planning; dental implants to replace missing or unhealthy teeth – not to mention a more attractive appearance; gastric bypass surgery to reduce dangerous obesity; and many more examples. Patients may not make such decisions lightly, but once they have recovered from the procedure, their responses to a “new life” range from satisfied to pleased to downright delighted when their purpose is achieved.

Intervening in the brain to stop tremors

The brain is the “Command Center” for all things physical, mental and emotional. It is protected from harm by bone and a cushion of fluid. We naturally cringe at the thought injuring it. But tremors are the result of abnormal physical brain transmission. The signals travel along a largely-known physical route in the brain called the tremor pathway, which includes the thalamus deep in brain. The thalamus, or a small part of it, is the target of ET treatments like DBS and FUS. Thus, a physical intervention within the brain itself can block tremor signals from reaching the hand.

In terms of physical intervention, let’s compare “reversible” DBS and “irreversible” FUS when it comes to treating ET. The National Tremor Foundation offers this description of DBS neurosurgery procedure (once a patient has been carefully qualified as a candidate):

…the patient undergoes a series of brain scans … which allows the surgeon to decide exactly where to place the electrodes in the thalamus. … These scans help the team to plan the route and the final position the wire(s) will take, avoiding other important areas of the brain next to where the wire(s) need to be.

…One or two small burr holes are made on either side of the skull. The electrodes are passed through these, down to the target area in the thalamus. There are four in-line electrodes at the end of a DBS lead. The aim is to introduce as many as possible of them within the depth and volume of the target area. The exact placement for the electrodes is then decided from the scans and other tests carried out in the operating theatre. When the electrodes are in the right place, the holes are closed and the other end of the DBS™ leads (not containing the electrodes) are connected individually to one or two extension cables. The extension cable(s) are tunnelled underneath the skin behind the ear, on the same side of the neck to the chest wall. The extension(s) are connected to the [power unit] which is then put into a small ‘pocket’ made under the skin. All the wounds are closed and dressed.

The patient usually then has another scan to check that the electrode(s) are in exactly the right place. They are transferred to recovery for a brief period of observation before being transferred onto a neurosurgical or neurological ward. …

What happens next depends on the centre where the surgery takes place. The stimulator may be programmed with an initial set of electrical parameters, either straight away or within a few days. A physician programmer uses radio waves to ‘talk’ to the implanted [power unit]. This is not painful or invasive. The physician can then adjust many variables of the stimulation, including which electrodes are selected, to ensure that the best effect is achieved. It is usual for the patient to need many adjustments over the next few months to optimise the therapy.i

A few additional comments about DBS: where holes were drilled in the skull, small plastic plugs are left in the holes; a brief hospital stay (usually overnight) is required; if the batteries in the power unit wear out, they must be surgically replaced; aside from inserting wires in the brain and leaving the electrodes in place to create the electrical stimulation that controls hand tremors, no brain tissue is destroyed though DBS comes with a small risk of stroke or infections. And yes, DBS can be surgically modified or reversed if electrodes move out of place, side effects persist, or a new treatment comes along.

On the other hand, FUS is an outpatient procedure (no hospital stay) without skin cutting or hole drilling. Instead, MRI is used to identify a tiny area of the thalamus called the VIM nucleus. Under MRI guidance, 1,000 beams of ultrasound are aimed from all different directions at the VIM nucleus. Each beam passes harmlessly through the skull and the brain tissue, but when they converge (meet) at the target, they create enough heat to precisely ablate (destroy) it. With the VIM nucleus deadened, the hand tremor signals are blocked and the hand functions normally. FUS is a selective treatment that blocks abnormal transmissions while preserving all other normal functions, so there is no future need to reverse it.

Each treatment has unique advantages and risks. However, irreversibility should not scare someone off from the benefits of FUS. For more information or to set up a consultation, see our website.

ihttps://tremor.org.uk/deep-brain-stimulation-faq.html

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