Movement disorders such as Parkinson’s disease (PD) and essential tremor (ET) are not yet curable. Thus, the goal of treatment is symptom management. In both PD and ET, the first approach to controlling tremors is generally medication. For PD patients, medication is almost always immediately effective. For persons with ET, however, drugs may prove disappointing from the very start. Only about half of those with ET feel like pharmaceuticals offer good tremor control, while the other half go through a version of “pill roulette” only to opt out of medication altogether. Even when the drugs help, side effects from gradually increasing doses may prove intolerable for many who then give up on drugs.
When pharmaceuticals are no longer effective—or a person does not want medication—a doctor may suggest a neurosurgical procedure to interrupt tremor signals in the brain (neuromodulation).
Deep brain stimulation (DBS)
The science of neuromodulation got a huge boost in 1997 when the U.S. Food and Drug Administration (FDA) approved Deep Brain Stimulation (DBS) to treat tremors due to PD and ET. In DBS, tiny electrodes are surgically implanted in the brain. When connected by wires in the neck to a “power pack” inserted beneath the skin of the chest or abdomen, the electrodes deliver electric impulses to a small area of the thalamus gland. The impulses modulate the tremor signals to allow normal movement signals to reach the affected hand.
Benefits and risks of DBS
By 2018, it was estimated that over 150,000 DBS implants had been done globally, not just for tremors but also to treat other neurological disorders such as dystonia and epilepsy.i The large number of patient records accumulated during the last 20 years lends itself to an analysis of the benefits and risks of DBS, both short- and long-term.
DBS works for most patients. When the electrodes are appropriately placed and tested at the time of the surgery, the majority of patients immediately experience greatly reduced or complete cessation of tremors. Another benefit of DBS is the ability for the patient to modify the settings via a hand-held control. Once the electrodes have been programmed for maximum symptom relief with minimum side effects such as facial tingling, the patient can regulate symptom control depending on the situation.
However, as with any invasive neurosurgery, there are risks. In the short term, there is slight chance of infection, bleeding in the brain, headaches, and physical side effects that usually quickly diminish. But, in addition to occasional batter replacement, longer-term hardware problems can occur, including electrode migration and component malfunction. There is also an ongoing risk—though very small—of having a stroke.
Sometimes, it is necessary to surgically correct the location of the electrodes, or completely remove the advice. According to a study of 123 DBS patients in one center, and a comparison of the center’s experience vs. a review of published literature, “Annual hardware removal rates were 3.6 and 2.4% for per-study and per-patient analysis, respectively, and lead revision rates were 4.1 and 2.6%, respectively.”ii
Discovering another long-term problem
Recently, a new long-term problem has been identified. The power of DBS to control ET fades over time. A March, 2019 published article by a German research team tracked 20 ET patients from pre-surgical baseline through up to 10 years of follow-up.iii Patients were evaluated (with stimulation on and off) using the Tremor Rating Scale (TRS), the Archimedes spiral drawing, and the activities of daily living score. They found that despite significant initial tremor improvement, its severity worsened over time. Of special concern, “Long-term worsening of the TRS was more profound during stim-ON than in the stim-OFF condition, indicating habituation to stimulation.” In other words, the brain adapted to the stimulation in such a way that it lost its effect over the long term.
Focused ultrasound: a non-surgical alternative to DBS
A growing number of people with ET who are not satisfied with medication—or whose drugs no longer work—are turning to a noninvasive, MRI-guided brain treatment called focused ultrasound. Instead of implants in the brain to modulate tremor signals, beams of ultrasound can be aimed at the same area to deaden the “relay station” so the affected hand regains steadiness. This targeted treatment does not affect normal brain signals. Since there is no drilling or implantation, it is done on an outpatient basis with no danger of infection or brain bleed.
For more information on this durable alternative to DBS, visit our website.
iiEngel K, Huckhagel T, Gulberti A, Pötter-Nerger M et al. Towards unambiguous reporting of complications related to deep brain stimulation surgery: A retrospective single-center analysis and systematic review of the literature. PLoS One. 2018 Aug 2;13(8):e0198529.
iiiPaschen S, Forstenpointner J, Becktepe J, Heinzel S et al. Long-term efficacy of deep brain stimulation for essential tremor: An observer-blinded study. Neurology. 2019 Mar 19;92(12):e1378-e1386.