The latest evidence on target selection in deep brain stimulation for Parkinson
Lukins TR, Tisch S, Jonker B. The latest evidence on target selection in deep brain stimulation for Parkinson , Neurosci. 2014 Jan; 21(1):22-7. doi: 10.1016/j.jocn.2013.05.011. Epub 2013 Nov 5.
Intro: This article begins with an overview of the strengths and weaknesses of typical medicinal and surgical treatment for PD. Traditionally DBS has been a secondary treatment option after medicinal therapies are no longer effective or there are disabling side effects for the person with PD. However, studies are beginning to show that there may be beneficial effects to implement surgical treatment earlier in the disease course. Researchers also have varied in surgical target selection and it is thought that a “one size fits all” approach is no longer adequate. The author’s purpose was to discuss the typically chosen surgical targets for DBS in PD.
Methods: Research articles were reviewed from 1999 to 2013 and summarized by surgical target.
- Subthalamic Nucleus (STN) and Globus Pallidus Interna (GPi): The STN and GPi have received the most research regarding DBS and have consistently shown improvement in motor symptoms of PD. A large multicenter Veterans Affairs trial found that there was not a significant difference between the two targets to improve motor function, on quality of life, or adverse effects. Some differences found were that the STN group required a smaller dosage of dopamine therapy after DBS, they had a higher depression score, and their processing speed was slower. On a second randomized study (COMPARE trial), it was found that there really were no differences in mood scores but the STN group had worsened speech fluency. Other smaller studies were discussed with generally similar findings with some slight differences. Regarding adverse events, the authors purport that there is significant variability within the studies but generally, that DBS STN is more likely to have increased “depression, impulsivity, fatigue, paresthesias, weight gain, and edema.” A long-term study also showed that DBS STN had a reduced need for dopamine therapy and “greater improvements in tremor, rigidity, akinesia, postural stability, and gait” after 5-6 years compared to the DBS GPi group.
- Pedunculopontine nucleus (PPN): Research on this target is much less but it remains a target of interest as it possibly could improve gait disturbances. One study found that stimulation of both the STN and PPN was beneficial but has only been completed in a small number of patients. Regarding adverse events of this target, dysaesthesias were the most common. Multiple studies with small patient numbers were discussed but randomized control trials need to be completed for more conclusive information on this target.
- Thalamus: The target discussed was the ventral intermediate nucleus (VIM) of the thalamus. The studies reviewed suggested long-term improvement specifically for tremor but not the other features of PD. Adverse events were low, 4% of the 73 patients experienced an intracranial hemorrhage, and others noted mild speech and stability difficulties. This is a target predominant for essential tremor and is rarely done for PD.
- Posterior subthalamic area (PSA): Target areas include the zona incerta (Zi) and prelemniscal radiations. One study found that stimulation of the PSA improved tremor in those that had essential tremor but people with PD (PWP) were not included in that study. Another study found that Zi stimulation improved “tremor, rigidity, and bradykinesia” in those with parkinsonism but again PWP were not evaluated.
- Centre median-parafascicular complex (CMPf): This region of the thalamus was stimulated in rats and was found to improve pain, attention, tremor, and dyskinesias.
Conclusion: There isn’t a one-size fits all approach to DBS and the procedure should be tailored to the individual patient’s symptom presentation although the targets of most promise continue to be the STN and GPi. Continued randomized clinical trial research on the above noted targets will provide more information on treating the motor and nonmotor symptoms of PD.