Flash visual evoked potential monitoring of optic tract function during macroelectrode-based pallidotomy

Time for a New 3-D Image for Globus Pallidus Internus Deep Brain Stimulation Targeting and Programming

Deep brain stimulation (DBS) is an effective neuromodulatory therapy for Parkinson’s disease (PD). Early studies using globus pallidus internus (GPi) DBS for PD profiled the nucleus as having two functional zones. This concept disseminated throughout the neuromodulation community as the “GPi triangle”. Although our understanding of the pallidum has greatly evolved over the past 20 years, we continue to reference the triangle in our clinical decision-making process. We propose a new direction, termed the spatial boundary hypothesis, to build upon the 2-dimensional outlook on GPi DBS. We believe an updated 3-D GPi model can produce more consistent, positive patient outcomes.

Electrophysiology of Olfactory and Optic Nerve in Outpatient and Intraoperative Settings

Evoked potentials are time-locked electrophysiologic potentials recorded in response to standardized stimuli using scalp electrodes. These responses provide good temporal resolution and have been used in various clinical and intraoperative settings. Olfactory evoked potentials (OEPs) may be used as an adjunct tool in identifying patients of Parkinson disease and Alzheimer dementia. In clinical practice, visual evoked potentials (VEPs) are particularly useful in identifying subclinical cases of optic neuritis and in treatment surveillance. In recent times, pattern electroretinograms and photopic negative response have been gaining attention in identifying glaucoma suspects. During surgical manipulation, there is a risk of damage to optic or olfactory nerve. Intraoperative neurophysiologic monitoring can provide information regarding the integrity of olfactory or visual pathway. OEPs and VEPs, however, show high degree of variability and are not reliable tools because the responses are extremely susceptible to volatile anesthetic agents. Newer techniques that could possibly circumvent these drawbacks have been developed but are not used extensively. In this article, we briefly review the available techniques to obtain OEPs and VEPs, diagnostic applications, the utility of intraoperative monitoring, the limitations of the current techniques, and the future directions for research.

Outcomes after stereotactically guided pallidotomy for advanced Parkinson's disease

OBJECT

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that becomes refractory to medication as the disease progresses. Although in the past 5 years increasing numbers of patients have undergone stereotactically guided posteroventral pallidotomy for advanced PD, the safety and efficacy of surgery remains to be documented. The goal in this study was to determine the potential operative morbidity and types of functional outcomes by using validated PD rating scales and a patient survey.

METHODS

In a prospective analysis of a consecutive surgical series the authors evaluated 58 patients with advanced PD who ranged in age from 40 to 79 years (mean 67 years) and who had undergone surgery between 1994 and 1997. They used a patient survey and the Unified Parkinson's Disease Rating Scale (UPDRS) to study patients during periods of medication administration ("on") and withdrawal ("off"; mean off score before surgery = 96). Temporary surgical morbidity was found in four patients (6.9%), three of whom developed transient dysarthria and one of whom exhibited transient confusion (1.7%). One patient had persistent dysarthria (1.7%). No patient developed a visual field deficit or sustained a brain hemorrhage. All patients were discharged from the hospital within 24 hours. Significant postsurgical improvements were noted in the UPDRS off-period total and motor scores, as well as in tremor, rigidity, bradykinesia, and contralateral dyskinesia (p < 0.005). Improvements persisted in dyskinesia and tremor for the 21 patients who were evaluated past 1 year. The authors found no improvement in any on-period symptoms except dyskinesia. Thirty-one (61 %) of 51 patients surveyed reported functional gains and/or dramatic improvement in symptoms, 17 (33%) reported symptomatic improvement without functional gains, and three (6%) had minimal or no change in symptoms. No change in the mini mental state examination score was noted during follow up. There were no significant postoperative changes in the use of medication.

CONCLUSIONS

In advanced PD associated with either a medically refractory state with significant off periods or levodopa-induced dyskinesias, magnetic resonance imaging-guided pallidotomy with macrostimulation was associated with minimal morbidity and yet significantly reduced dyskinesia and off-period disability. These improvements were of value to the patient and persisted beyond the 1st year.