Since the FDA approved deep brain stimulation (DBS) for essential tremor and Parkinson’s tremor in 1997, it has become an increasingly valuable tool in caring for patients with neurological disorders.
Five years after the initial FDA approval, advanced Parkinson disease associated with motor complications was added to the list of indications, followed by dystonia in 2003, and obsessive-compulsive disorder in 2009. Most recently, in 2016, the FDA added mid-stage Parkinson disease (PD) of at least four years duration to the list of uses for DBS. According to Leo Verhagen Metman, MD, PhD, Professor of Neurological Sciences at Rush University Medical Center, adding this last indication for the earlier stage of PD was controversial because there is more to choosing a treatment than duration of disease.
DBS Patient Selection in Essential Tremor and Dystonia
For essential tremor and dystonia, picking the right patients is relatively easy compared to this newer indication for mid-range PD. Essential tremor is characterized by a single symptom, and we have no other reliable treatments for it. This makes DBS a fairly straightforward choice. While age or comorbidities may contraindicate the treatment for some, DBS is often the best choice for most, if the tremor is disabling.
The situation is similar for dystonia. When there is no known structural abnormality in the brain, patients seem to do very well with deep brain stimulation, regardless of type.
Patients with secondary dystonia don’t respond as well to DBS because a structural abnormality is present. But this distinction is usually fairly clear, making the decision straightforward.
Selecting appropriate patients with mid-stage PD is more complicated.
DBS Patient Selection in Parkinson Disease
In his presentation to the American Academy of Neurology in 2018, Metman explained that mid-stage PD is an important indication to understand. Patients with PD may feel DBS is the automatic next step, since the FDA has stated that it is indicated after the disease has been present four years. And data show that mid-stage PD patients have better results with DBS than those with optimal medical treatment. But as Metman emphasizes, this can’t be taken as a general recommendation. Other factors determine if DBS is appropriate for a patient—this is true whether they’ve had the disease for four or eight or twelve years. The FDA’s indication doesn’t mean that after four years every Parkinson patient should undergo DBS.
It is the movement-disorder specialist who makes the determination whether maximum benefit has been seen from medications. One key consideration for the specialist, though, is what the patient’s goals are. They may not match those of the specialist.
For example, Metman explains that to the specialist, a tremor may appear to be the most significant symptom for a patient with PD. But the patient might actually be more concerned about other issues that won’t respond well to DBS, such as speech difficulties.
For this reason, the collaboration between specialist and patient is important. Combining the patient’s priorities with good patient selection can help identify the cases with the greatest potential for benefit from DBS.
He continues, “We still believe that the response of each individual symptom to Levodopa somewhat predicts the outcome of DBS. The exception there is tremor. That always gets better with DBS, even if it doesn’t respond to Levodopa.”
Red flags do come up when dealing with atypical PD, where certain symptoms are unresponsive to Levodopa. A typical case is when the patient may feel better, but in the on-state, they’re still falling, they still have balance difficulties, they still have gait problems. That is usually not a good indication for DBS.
Additionally, when a patient is suffering from dementia, severe depression, or psychosis, these issues should be addressed first. Then the patient can be re-evaluated for the appropriateness of DBS.
As our understanding of the effects of DBS grows, so will its uses. Indications on the horizon include epilepsy, Tourette syndrome, Alzheimer disease, depression, and more. Establishing a pattern of methodical DBS patient selection will help current and future DBS patients gain the most benefit with the least risk.