What were the results of the study?
Platz: After completing six weeks of therapy, researchers looked at how patient arm function had improved. They primarily used an arm movement test called the Fugl-Meyer Assessment, which is an accurate measure of targeted arm recovery in sequential stages. It is the international standard that evaluates and measures motor recovery in post-stroke patients. The researchers also performed the Wolf Motor Function Test.
Both patient groups were able to improve arm function thanks to the training. The patients who had received the stimulation had improved their scores twice as much compared to the other group. This is a clinically important difference that has shown to be very stable. The stimulation significantly increases the therapeutic effects of the rehabilitation exercises.
What happens in the body when the exercises are accompanied by stimulation?
Platz: While this cannot be deduced from the study itself, there has been animal testing on rats in the past. The rodents exhibited front foot impairment after an induced stroke. The animals subsequently saw an improvement of front foot function with stimulation. The synapse connections in the motor area of the brain of rats treated with stimulation were also observed to be more active.
Therefore, the assumption is that the vagus nerve uses its many fibers to pass stimuli into the brain. The excitation of electrical stimulation arrives in the brain stem and gets to the cerebrum via various signaling pathways, thus promoting changes in its activity. When it comes to voluntary movements - such as exercises with the stroke-impaired arm -, it is essential that the cerebrum and the brain networks responsible for movement are active to improve and recover motor control.
What is next for this application in your opinion? How do you rate its possibilities?
Platz: The study has yielded very promising results. It has shown that people with arm paralysis can achieve relevant improvement in arm function even long after a stroke. That is a very positive sign, regardless of vagus nerve stimulation.
The study’s definitive and consistent results also indicate that stimulation significantly enhances the effects of rehabilitation with little or no side effects and promotes great treatment acceptance by patients.
This gives rise to a new approach. However, I do not think the study results are a jumping-off point to turn them into a routine approach just yet. It is cost-intensive, invasive and has possible surgical risks, but it sends an important signal: when accompanied by additional examinations, this might become a brand-new treatment option. The next step would be to test external vagus nerve stimulation through the skin, thus avoiding the need for an implant. The treatment could be used more extensively if this yields similar effects, and if the process is just as safe and well-tolerated.