Electrical Stimulation for Parkinson's
Electrical Stimulation of the Brain Can Benefit Some Persons with Advanced Parkinson's Disease
What is the problem and what is known about it so far?
Parkinson's disease results from the gradual loss of nerve cells in a region of the brain called the "substantia nigra", where a chemical called dopamine is produced. Dopamine is critical for motor function (ability to move). The low levels of dopamine present in patients with Parkinson's disease results in loss of facial expression, stooped posture, slowness of voluntary movement, rigidity, and tremor. Levodopa, a chemical that turns into dopamine, is the usual treatment for Parkinson's disease. Although it is used to boost dopamine levels in the brain, it also causes long-term disorders of movement.
Why did the researchers do this particular study?
The authors of this study have previously reported short-term improvements in motor function when a separate but geographically-related region of the brain called the subthalamic nucleus is electrically stimulated. This improvement was noted when patients were taken off medication as well as while on it. The present study was performed to see how this treatment works in the long run.
Who was studied?
Forty nine patients who had received electrode implants for electrical stimulation therapy between 1993 and 1997 took part. All had had clinically diagnosed Parkinson's disease, complications from levodopa treatment, were less then 70 years of age, had no health reasons that would have prevented the performance of the surgery, and no dementia or major ongoing psychiatric illness.
How was the study done?
Patients were evaluated before and after surgery at one, three and five years according to a standardized Parkinson's Disease Rating Scale. Patients were electrically stimulated throughout the study period. At each evaluation motor function was assessed with patients on and then off medication for a period of 8-12 hours. The on-medication evaluation was done with patients taking a dose of levodopa that was 50 percent higher than their usual morning dose to simulate a period of maximal clinical benefit from the drug. During these evaluations neuropsychological tests were also performed to assess cognitive (thinking) ability, mood, and behavior.
What did the researchers find?
To evaluate the effect of the treatment, investigators measured activities of daily living and motor function. When patients were off-medication, motor function improved at all three times after having the electrodes implanted and receiving the electrical stimulation compared to before the procedure. This improvement was sustained over the five-year evaluation period. Measures of the activities of daily living also showed an improvement at all three evaluation times when patients were not taking medication. Five years after surgery most patients were independent in their daily living activities when off medication. However, the level of improvement after five years was not as good as after one year. The electrical stimulation did not improve motor function or activities of daily living when patients were taking medication but did allow for a decrease in the amount of medication required and reduced side effects from the medications.
What were the limitations of the study?
Patients and evaluators in this study were not blinded (they knew who was receiving the treatment), potentially resulting in some bias in the report of functional improvement. There was no control group but the disease almost always progresses with time.
What are the implications of the study?
Electrical stimulation of the subthalamic nucleus can reduce movement disorders from both the disease process and the medications used in those with Parkinson's disease. However, overall function does worsen with the progression of the disease. This therapy seems most useful for relatively young patients who experience complications from levodopa treatment and who are independent in activities of daily living when taking medication. This treatment should not be recommended for patients who already have disabling movements that are resistant to levodopa treatment or who have worsening cognitive disorders.
Summarized by Stanley Kang, College of Medicine, University of Vermont.
Summarized from " Five-Year Follow-up of Bilateral Stimulation of the Subthalamic Nucleus in Advanced Parkinson's Disease" Krak, P. et al. New England Journal of Medicine, November 13, 2003, Volume 349, Number 20, Pages 1925-1934.
