A new study has found that patients with Parkinson's disease who continue to experience difficulties after electrode implantation could be helped by additional surgery to position the electrode.
Electrodes implantation that stimulates the subthalamic nucleus, a region deep in the brain potentially related to impulsivity, can effectively reduce medication doses and improving the symptoms of Parkinson's disease.
"The principal cause of these poor results arises from imprecision of electrode placement, leading to non-stimulation of the target as required," wrote the authors.
"Misplacement of the electrode by only a few millimetres may have occurred," they added.
The study led by Dr Mathieu Anheim, of the University Hospital A. Michallon, Strasbourg, France involved seven patients aged 49 to 70 with Parkinson's disease who, showed poor response despite electrodes implantation.
The patients were operated on again and the electrodes were re-implanted 12 to 23 months after the original surgery.
The study showed that all patients except for one displayed improvement after the second surgery.
When not on medication, patient's motor scores also improved by 26.7 percent following the first operation and 59.4 percent following the second procedure.
The dose of levodopa, a medication treating Parkinson's disease also decreased from 1,202 milligrams to 534 milligrams.
The average distance between the electrodes and the target point of stimulation-a location in the subthalamic nucleus identified by evaluating electrode placement in patients also decreased from 5.4 to 2 millimeters.
The shorter this distance, the greater the patient's improvement in motor scores.
"Although appropriate patient selection is important for the desired surgical outcome, the key to marked improvement following subthalamic nucleus stimulation is optimal surgical technique for precise implantation of stimulation electrodes in the target," wrote the authors.
"Patients demonstrating poor response to subthalamic nucleus stimulation as a result of electrode misplacement can benefit from re-implantation in the subthalamic nucleus closer to the theoretical target," the added.
The report appears in the May issue of Archives of Neurology, one of the JAMA/Archives journals.