Deep brain stimulation is a surgical procedure used to treat tremors when other medications have been ineffective. It has been approved by the U.S. Food and Drug Administration for the treatment of Parkinson’s disease and essential tremor. It may also be used to treat tremors in multiple sclerosis (MS).
Tremors affect about 30% of MS patients. It is often accompanied by other movement disorders such as ataxia (poor coordination) and dysmetria (inability to judge distances). In general, tremor in MS is attributed to damage to nerve cells in a section of the brain called the thalamus.
How deep brain stimulation works
Deep brain stimulation involves surgery to permanently implant electrodes in the thalamus. A battery is also implanted near the collarbone, which sends electric pulses to the electrodes that interfere with the abnormal nerve signals that are causing tremors.
Deep brain stimulation may reduce tremors, but may not eliminate other disabling symptoms such as ataxia and dysmetria. Some patients may develop new symptoms, such as speech and swallowing disorders, and balance problems. Patients may also develop a tolerance to the electrical signals over time. This means they must frequently return to their doctor’s office to have the impulse generator reset to a higher or lower level. There is a low risk of infection, and about 2–3% of patients may experience a brain hemorrhage.
A randomized pilot trial (NCT00954421) conducted at the University of Florida investigated the safety and efficacy of dual-lead thalamic deep brain stimulation in treating MS-associated tremor. A total of 12 patients were randomly assigned to three initial months of stimulation in two different areas of the brain. Tremors were assessed before the operation and at three and six months after dual-lead thalamic deep brain stimulation using the Tolosa-Fahn-Marin tremor rating scale (TRS). The primary outcome of the study was the change in the mean TRS score at the six-month assessment following the operation with both leads activated, compared with the mean TRS score before the operation.
The mean TRS score decreased from 57 before the operation to 40.1 six months after the procedure. This meant that there was a 29.6% reduction in tremors. The researchers concluded that deep brain stimulation was a safe and effective option for alleviating severe tremors in MS. However, large-scale studies are still needed to establish the effectiveness of deep brain stimulation in treating tremors in MS patients because the sample size in this trial was small, and a few adverse events were reported.
The most common non-serious adverse events were headache and fatigue. Serious adverse events included a superficial wound infection in one patient that was resolved with antibiotic therapy, and transient altered mental status and late MS exacerbation in another patient. One patient developed an infection and had to be excluded from the analysis. Three of the remaining 11 patients did not respond to surgical intervention. One patient died suddenly two years after surgery, but this was deemed unrelated to deep brain stimulation.
Another clinical trial (NCT02553525) is measuring the effects of non-regular temporal patterns of deep brain stimulation on motor symptoms and neural activity in patients with Parkinson’s disease, essential tremor, or MS. The study is being conducted in Florida, Georgia, and North Carolina, and is enrolling participants by invitation only. It is expected to be completed in August 2019.