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Science News

Deep Brain Stimulation at Two Sites Improves Parkinsonís Symptoms Over Long Term

Fifteen years after its approval by the United States Food and Drug Administration, deep brain stimulation (DBS) remains the most advanced and effective treatment for people with Parkinson’s disease (PD) who experience severe motor fluctuations and dyskinesias.  According to a study published in the July 3 issue of Neurology, which compared two sites in the brain that can be targeted for DBS in Parkinson’s, both locations show near-equal results after three years.

DBS consists of providing a tiny electric current to structures of the brain in order to block motor symptoms of PD.  Investigators and clinicians have long known that two sites deep inside the brain – the subthalamic nucleus (STN) and the internal globus pallidus (GPi) – have the broadest antiparkinsonian effects when stimulated by an implanted electrode.  The questions remain: what is the best site to implant the electrodes?  And which gives the longest lasting results?

The new study provides the first randomized, long-term, head-to-head comparison of GPi and STN DBS for the treatment of Parkinson’s.  In the new study, researchers led by Frances Weaver, Ph.D., director of the Center for Management of Complex Chronic Care at Hines VA Hospital in Illinois, randomly assigned 299 people with PD to receive either STN stimulation or GPi stimulation. Over the long-term, a smaller group of 159 people were available for careful follow-up.  The participants reported their daily symptoms in a journal and returned to the clinic for motor and neurocognitive assessments at three, six, 12, 18, 24, and 36 months.

Results:

  • People treated with GPi or STN DBS showed similar long-term improvements in motor function.  In both groups, individuals experienced a sustained 32 percent reduction in their motor symptoms three years after surgery.
  • In both groups, quality of life and neurocognitive measures gradually declined over time, suggesting progression of the non-motor features of PD.
  • Scores of cognitive function declined slightly faster for individuals with PD in the STN group than for those in the GPi group.
  • People in the STN group were able to reduce their levodopa medication to a greater extent than those in the GPi group (35 percent versus 18 percent reduction).  When the study participants were evaluated at 36 months in the experimental state of being off their medication, and with the DBS devices turned off, the STN group’s motor scores appeared slightly worse than those individuals who had undergone GPi stimulation.

What Does It Mean?

Since the first report of deep brain stimulation, which featured the subthalamic nucleus, the preferred target for deep brain stimulation has been the STN.  The new study shows that people who undergo DBS at either the STN and GPi targets experience similar long-term improvements in motor function.  STN DBS allows people to more drastically reduce their levodopa medication, which can help alleviate troubling side effects in selected individuals.

This study suggests that the GPi should be reconsidered as a target for DBS, although further studies are needed to verify these results.  Stimulation of the GPi may provide additional benefits, such as reduced cognitive decline.  STN DBS may remain the preferred treatment for those with severe resting tremor because this symptom is probably more sensitive to STN than GPi stimulation.

In randomized clinical trials, the scientific truth depends on a balanced assignment of participants to each treatment group.  In this study, 50 percent of study participants originally randomized in the study dropped out or were lost to follow-up, an issue that may have influenced the results. Also, in the quality of life assessments conducted at the beginning of the study, individuals randomly assigned to STN surgery rated themselves as having a significantly lower quality of life, using the Parkinson’s disease rating scale (UPDRS), than those assigned to GPi stimulation, a difference in assignment that might have affected the results.

For people with Parkinson’s who are considering DBS, it should be a comfort to know that whichever target is recommended – STN or GPi – the benefit will be equal.  Further study with larger numbers of participants would be needed to know whether one target is superior for selected individuals.

Reference: Weaver, F. M., Follett, K. A., Stern, M., et al. (2012) Randomized trial of deep brain stimulation for Parkinson disease: Thirty-six-month outcomes. Neurology. ADD DOI

Source Date: Jun 20 2012