David Charles, MD, and Thomas Davis, MD, of the Vanderbilt University Department of Neurology, recently spoke with Neurology Reviews about the treatment pipeline and latest research in levodopa-induced dyskinesia in Parkinson's disease.
How is the treatment pipeline advancing for different types of levodopa-induced dyskinesia (LID)?
Dr. Thomas Davis: Dyskinesia has traditionally been hard to quantify, and we have been lacking any US Food and Drug Administration (FDA)-approved anti-dyskinesia drugs. The pipeline has historically been strongest for wearing-off because it is easier to measure on time than to quantify involuntary movements.
The Unified Dyskinesia Rating Scale (UDysRS), released in 2008 by the Movement Disorder Society, provided a standardized scale that allowed dyskinesia clinical trials to move forward. The UDysRS was used as the primary outcome for the extended release amantadine capsule study. This was important because it demonstrated the possibility of a successful clinical trial design to get a drug approved for dyskinesia, which will encourage others to test more potential new treatments.
What is the status of research on deep brain stimulation (DBS) for Parkinson's disease, and when might it be considered?
Dr. David Charles: This is one of the areas of research that we're focused on here at Vanderbilt. All 3 of the FDA-approved device manufacturers have been conducting research in technology refinement and improvements. These advances include not only patient programmers and physician programmers, but also new sensing capability and lead designs. Some of the manufacturers now have leads that allow the physician to steer the current in one direction or another, where traditionally the current has been delivered in a circumferential contact that's shaped like a cylinder, where the energy is transmitted 360 degrees from the lead. The new designs allow you to steer the current hopefully toward areas that provide more efficacy and away from areas that cause side effects. Even more exciting is the emerging sensing capability that may allow the development of stimulating technology that is responsive to fluctuating symptoms. There is keen research interest in understanding whether a device could detect a specific neuronal firing pattern and then respond with an individually tailored stimulation to improve symptoms as needed. Will the next generation of deep brain stimulating devices detect the pattern and deliver energy in a more targeted and precise way, responsive to what it's sensing from the patient's brain? I think that's an area of research that's really exciting.
In regard to when it might be considered: The ability to steer the current is already available in 2 of the 3 systems that are on the market today. Having current that is steerable in all 3 will be coming in the not too distant future. The available devices already have improved programming platforms for health care providers as well.
Our research at Vanderbilt is focused on DBS in early-stage Parkinson's disease. There is a paper published in Neurology that reports Class II evidencet hat DBS applied in early-stage Parkinson's disease slows the progression of tremor. This is exciting because none of the available treatments change the progression of disease—they're currently accepted as symptomatic therapies only. In this publication, we report that participants receiving DBS in the very earliest stages of Parkinson's disease it may slow the progression of rest tremor. We now have approval from the FDA to conduct a large-scale phase 3, multicenter, clinical trial of DBS in early-stage Parkinson's disease, with the primary endpoint focused on slowing progression of tremor, a cardinal feature of the disease. This upcoming trial is approved by the FDA as a pivotal trial, meaning that the findings could potentially be used to change the labeling of DBS devices. Our goal is to obtain Class I evidence of slowing the progression of tremor or other elements of the disease.