Deep brain stimulation via electrodes implanted on both sides of the brain markedly improves the motor skills of patients with advanced Parkinson's Disease, says a new long-term study by researchers at the University of Toronto and Toronto Western Hospital.
"We saw a pronounced decrease in the motor scores associated with Parkinson's Disease - the tremors, stiffness and slowness - and this benefit was persistent through the course of the long-term followup," says Dr. Anthony Lang, professor in U of T's division of neurology, the Jack Clark Chair in Parkinson's Disease Research at the Centre for Research in Neurodegenerative Diseases and director of the Movement Disorders Clinic at Toronto Western Hospital, University Health Network. He and his colleagues used the Unified Parkinson's Disease Rating Scale (UPDRS) to evaluate both the features of the disease as well as the side-effects of medication. They found motor scores decreased an average of 48 per cent. "This is quite substantial when you compare it to other trials of therapy for Parkinson's Disease," he says.
In the September issue of the Journal of Neurosurgery, Lang and his colleagues describe the first long-term followup of deep brain stimulation on the subthalamic nucleus (one of the deep nuclei in the brain that sits just above the area known as the midbrain). The subthalamic nucleus is part of the group that co-ordinates automatic movements.
Between 1996 and 2001, Lang and his colleagues followed 25 patients who had electrodes implanted into the region of the subthalamic nucleus on both sides of the brain; the electrodes were wired under the skin to pacemaker-like devices. The frequency and intensity of stimulation was adjusted; patients were monitored and evaluated prior to and after surgery while on and off medication.
When patients were off medication, the UPDRS score - which measures both motor skills and the ability of patients to perform daily living activities - improved after one year, decreasing by 42 per cent. Medication requirements also diminished substantially - dosages were reduced by 38 per cent one year after surgery and 36 per cent at their last evaluation.
Researchers believe the reduction in medication dosage may also partly account for the significant decrease in dyskinesia scores. Dyskinesia - abnormal involuntary movements - are side effects of medications like levodopa where patients exhibit rapid and repetitive motions of the limbs, face and neck or display slow, involuntary movements of the hands and feet.
"One of the important features we found is that not all symptoms of Parkinson's Disease respond equally to treatment," notes Lang. "Over time, the tremors, stiffness and, to a lesser extent, the slowness continue to respond to surgery and medication. But certain features of the illness such as speech, stability and difficulty with walking benefit less from therapy over the course of long-term followup."
Lang warns that deep brain stimulation will not prevent the disease from worsening, slow its progression or prevent the development of later problems like dementia. However, he says that younger patients like the ones in their study (average age of 57 at the time of surgery) with advanced Parkinson's Disease did experience sustained improvement in motor function for an average of two years after the procedure as well as a reduced need for medication.
Dr. Andres Lozano, the holder of the R.R. Tasker Chair in Stereotactic and Functional Neurosurgery at U of T and a neurosurgeon at Toronto Western Hospital, co-directed this research with Lang and the other members of their team - Galit Kleiner-Fisman, Jean Saint-Cyr and Elspeth Sime of Toronto Western Hospital and David Fisman of McMaster University. This study was supported by the National Parkinson's Disease Foundation in the U.S., the Morton and Gloria Shulman Movement Disorders Centre at Toronto Western Hospital, the Jack Clark Chair in Parkinson's Disease Research at U of T, Medtronics in Minneapolis, Minn., and the Canadian Institutes of Health Research.