Deep brain stimulation (DBS) and high frequency ultrasound (HFUS, also called MRI guided focused ultrasound thalamotomy, MRgFUS-thalamotomy, or simply focused ultrasound) are two treatment options for essential tremor that can reducing tremors and improve quality of life.
Focused ultrasound is a newer treatment that is being marketed to patients as “non-invasive,” but this claim may be somewhat disingenuous as the rate of adverse events and permanent neurologic injury is higher with focused ultrasound than DBS as documented by several studies. Furthermore, DBS has a higher efficacy of tremor reduction than focused ultrasound and can effectively treat BOTH SIDES OF THE BODY. Focused ultrasound has higher adverse event rates than DBS treating ONLY ONE SIDE OF THE BODY. Dr. Taghva has experience treating patients with DBS who have failed focused ultrasound.
In a recent meta-analysis for focused ultrasound (HFUS or MRgFUS-thalamotomy) versus DBS (Giordano et al 2021). “Postoperative tremor improvement was greater following DBS than MRgFUS thalamotomy (p<0.001).” and “Persistent complications were significantly more common in the MRgFUS group (p=0.042).”
Here are some key differences between DBS and HFU for essential tremor:
Mechanism of Action
DBS involves implanting a small electrode into a specific area of the brain and using electrical stimulation to modulate the neural pathways responsible for tremors. HFU, on the other hand, uses focused ultrasound waves to burn a lesion or hole, in a specific area of the brain, disrupting the neural pathways responsible for tremors. Because of this, focused ultrasound, or MRgFUS-thalamotomy is IRREVERSIBLE AND PERMANENT and cannot be adjusted, whereas DBS is REVERSIBLE AND ADJUSTABLE. As historical reference, other forms of creating a hole in the thalamus were used before DBS, but were largely abandoned after the superior efficacy of DBS was demonstrated.
Safety record and long term follow up
DBS was approved by the FDA for essential tremor in 1997, and has been performed in over 80,000 patients worldwide. MRgFUS-thalamotomy was approved in 2016. The exact number of patients who have received focused ultrasound for essential tremor is not known, as the procedure is still relatively new and not yet widely available in all areas.
DBS is a procedure that requires surgery to implant the electrode into the brain. This surgery can be done with patients asleep or awake. It can safely treat tremor on BOTH SIDES OF THE BODY AT ONCE. HFU, on the other hand, is a procedure that must be performed awake while a patient is fixated in a metal frame, the entire head is shaved. Patients must be awake to monitor potential side effects, and only one side of the body can be treated safely at a time. It is currently being studied whether MRgFUS-thalamotomy can treat both sides of tremor safely, but even in this setting it must be performed with significant delay between both sides.
Targeting
DBS allows for precise targeting of the specific area of the brain responsible for tremors. Focused ultrasound also allows for precise targeting, but there is a greater risk of targeting errors due to factors such as skull thickness or movement of the target area during treatment.
Long-Term Efficacy
DBS has been studied extensively and has shown long-term efficacy in reducing tremors and improving quality of life in people with essential tremor. The long-term efficacy of HFU is still being studied, and it is not yet clear how long the effects of treatment will last. Data studying long term effects of focused ultrasound shows a significant stepwise decrease in efficacy over time at 3 years and 5 years (Halpern et al, Neurology 2018 and Cosgrove, J Neurosurgery 2023).
Adverse events are significantly higher for focused ultrasound than DBS. The most common side effects with focused ultrasound as described by Elias et al in the New England Journal of Medicine are paresthesia or numbness and tingling of one side of the body in 38% of patients, gait disturbance or difficulty walking in 36% of patients, dysmetria or lack of coordination in 12% of patients, tinnitus or ringing in the ears in 5% of patients. Other side effects included headache, taste disturbance, difficulty with speech or swallowing in 3-8% of patients. In fact, only 11% of patients in this study reported NO adverse events. This means, with focused ultrasound, 9 out of 10 patients reported an adverse event. Some of these got better with time, but many patients after focused ultrasound are left with a permanent neurologic deficit. A meta-analysis by Agrawal et al (Frontiers in Neurology 2021) demonstrated, after review of several studies, that long term complications of MRgFUS-thalamotomy or focused ultrasound in sensory function were 13% (range 7–23%), motor function 5% ( range 3–7%), ataxia or clumsy walking 31% (range 24–38%), and speech and swallowing dysfunction 5% (range 3–8%).
Side effects with DBS include gait disturbance in 14% of patients, temporary paresthesia in 6.5% of patients, and dysarthria (or speech difficulty) in 15% of patients (Kim et al, frontiers in neurology 2021). However, these side effects were REVERSIBLE with adjustment of stimulation and were far more common with stimulation of BOTH sides of the brain versus focused ultrasound where only one side of the brain was treated.
Overall, both DBS and HFU are treatment options for essential tremor that have shown significant tremor reduction and improved quality of life in many patients. However, the “non-invasive” claim of focused ultrasound masks the significantly higher complication rate of the procedure and the permanent nature of the side effects created. Furthermore, the efficacy in reducing tremor is provably higher with DBS. Luckily, Dr. Taghva has experience performing DBS after a failed high-frequency ultrasound. While it is unlikely that DBS can reverse any complications from focused ultrasound, tremor reduction can be improved with DBS after MRgFUS-thalamotomy.