Ablative brain surgery was used as early as 1912 to treat PD. When levodopa was introduced in the 1960s, surgical interventions for PD decreased dramatically. Within a few years, however, the therapeutic limitations of levodopa became apparent. With levodopa, PD continued to progress and treatment-related complications including
motor fluctuations and dyskinesias became a major therapeutic challenge. Neurosurgical intervention in the form of ablative procedures (for example, pallidotomy) became again popular among neurosurgeons. As the use of pallidotomy become widespread adverse effect of this procedure become evident like bilateral pallidotomy leading to speech impairment, balance and gait problems, visual field defects, and cognitive deficits. The search for safer and more effective surgical treatments, particularly for bilateral symptoms, leads to development of deep brain stimulation.
Deep brain stimulation, which involves the application of electrical stimuli, produces a functional lesion within a focal area of the brain. Two targets within the brain have been stimulated to treat PD: the STN and the GPI. Studies then have documented significant improvement in patient motor functioning and quality of life
following STN DBS. Serious adverse events have also been reported including infections, depression, mood changes, and psychosis requiring intervention as well as equipment issues such as lead fractures and dislodgements. GPI
stimulation have also reported improved motor
function and enhanced perceived quality of life. Serious complications reported for bilateral GPI DBS include hematomas, infections
and equipment issues. Data from an analysis of practice patterns confirm that DBS is now the preferred surgical treatment for PD. Significant questions regarding DBS remain, however, including which stimulation target site leads to better outcomes. It is not yet known whether certain
patients or particular symptoms respond better to stimulation of one target than another.
In absence of large randomized trials, a metaanalysis of patients operated for DBS was done. Inclusion criteria included the following factors: study patients had idiopathic PD, therapeutic intervention involved bilateral DBS of either the STN or the GPI, reported outcomes included UPDRS motor function scores off medications at baseline and off medications/on stimulation at follow up, and follow-up assessment occurred at least 3 months post-DBS. This metaanalysis includes 31 STN and 14 GPI studies. Motor function improved significantly following stimulation (54% in patients whose STN was targeted and 40% in those whose GPI was stimulated), with effect sizes (ESs) of 2.59 and 2.04, respectively. After controlling for participant and study characteristics, patients who had undergone either STN or GPI DBS experienced comparable improved motor function following surgery (p = 0.094). The performance of activities of daily living improved significantly in patients with either target (40%).
medication requirements were significantly reduced following stimulation of the STN (ES = 1.51) but did not change when the GPI was stimulated (ES = 20.02).
Data from an analysis of several dozen studies of bilateral STN and GPI DBS for PD indicated that motor function based on the UPDRS motor subscale improves significantly after DBS, regardless of the stimulation target. The beneficial effect was greater, although not statistically significantly so, in STN compared with GPI cases. Medication dosages were reduced by 50% following STN DBS but did not change in patients who had undergone GPI DBS. A differential effect of the stimulation target was found when medication requirements were examined. Medication requirements decreased in all studies following STN DBS but not following bilateral GPI DBS. In general, STN DBS allows reduced medication without adversely affecting motor function. Furthermore, STN DBS may exacerbate dyskinesias, and reduction of dyskinesias following this therapy is dependent on a reduction in PD medications. In contrast, GPI DBS may have a direct antidyskinetic effect that is not dependent on a reduction in medications, and many providers do not attempt to reduce medication in this group. Whether medications can be reduced following GPI stimulation without negative consequences has not been studied, nor have differences in medication requirements after STN and GPI DBS had been compared in a prospective, blinded fashion. Complications and adverse events of DBS are also important to consider in a comparison of STN and GPI stimulation. Subthalamic nucleus DBS has gained significant popularity and, based on improvement in motor function and de- creased medication requirements, the STN is considered the preferred site of bilateral stimulation by most PD specialty centers. Data from this analysis indicates that motor function improves equally in the GPI-targeted cases, while medication needs do not change.Given the promise of DBS for long-term management of advanced PD, clinicians and patients should make treatment decisions based on evidence from well-designed trials that minimize bias and provide valid findings to inform clinical practice
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