In people who have had deep brain stimulation (DBS) for the treatment of Parkinson’s disease (PD), lowering the stimulation settings may improve swallowing difficulties and freezing episodes when walking. The results of the new study appear in the January 27 edition of Neurology.
DBS involves surgically implanting electrical stimulators into the brain. It is a standard therapy for people with PD who have developed fluctuations in the effectiveness of levodopa (given as Sinemet®) and disabling dyskinesias (involuntary movements), and are otherwise healthy. Yet, even with DBS and medications, some PD symptoms remain difficult to treat.
For the new study, researchers led by Tao Xie, M.D., Ph.D., at the University of Chicago, tested the effects of decreasing the stimulation settings in seven people with advanced PD who had undergone DBS. All had DBS devices implanted on both sides of the brain in an area called the subthalamic nucleus (STN). In addition, study participants all had “freezing” episodes that did not respond to medication or to DBS at the typical setting, 130 Hz. Participants’ average age was 64 years, they had lived with PD on average for 13 years, and six of them were men. At the beginning of the study, while participants took their usual PD medication, the researchers tested a range of PD symptoms at three DBS settings: 1) 130 Hz; 2) 60 Hz; or 3) off. For the next eight weeks, participants kept their DBS stimulators at the setting at which they experienced the least “freezing.” Then all tests were repeated.
- Freezing of gait was significantly improved with DBS at 60 Hz.
- On questionnaires, study participants reported an 80 percent improvement in their ability to swallow with DBS at 60 Hz compared to 130 Hz.
- As viewed on a swallowing test (modified barium swallow study), DBS at 60 Hz reduced the frequency of aspiration (breathing in liquid when swallowing) by 57 percent compared to DBS at 130 Hz.
- For one participant, resting hand tremor worsened with DBS at 60 Hz; this participant returned to 130 Hz DBS after three weeks.
- These improvements lasted as long as DBS was set at 60 Hz.
What Does It Mean?
This study identifies a potentially simple way to reduce life-threatening risks of PD in a subset of people with advanced PD who have undergone DBS. Making swallowing easier for people with PD is important because breathing food or liquid into the airways can lead to pneumonia. Lessening “freezing” episodes is also critical, because freezing can increase a person’s risk of falls.
There are many parameters that can be adjusted when programming a person’s DBS stimulator, such as voltage intensity and stimulation frequency. Standard practice has been to use a high frequency stimulation, such as 130 Hz, when adjusting DBS settings because this is the frequency studies have shown best controls movement symptoms including tremor, stiffness and slowness.
Although the study was carried out in a randomized, double-blind manner – the most rigorous type of clinical study, the number of participants was small and the duration of the study was only several weeks, therefore one should be cautious in interpreting these results. For instance, more research is needed to determine whether lowering DBS helps swallowing in people who do not experience “freezing” and whether the benefit can last over a long term. Also, the authors note that people who have DBS to manage their tremors may not be able to reduce their stimulation level without the tremor worsening. Nevertheless, by exploring a greater range of DBS stimulation parameters, these investigators may be able to help pave the way to a reduction in the number of complications that people experience with advanced PD and DBS. Lastly, the study highlights an active area of basic research on novel brain circuits. Intervening on these circuits may help treat symptoms that have been beyond the reach of current therapeutic modalities.
Xie, T., Vigil, J., MacCracken, E., Gasparaitis, A., Young, J., Kang, W., Bernard, J, Warnke, P., Kang, U.J. (2014). Low-frequency stimulation of STN-DBS reduces aspiration and freezing of gait in patients with PD. Neurology. doi:10.1212/WNL.0000000000001184