Pallidotomy microelectrode targeting: Neurophysiology-based target refinement

OBJECTIVE: Microelectrode recording can refine targeting for stereotactic r adiofrequency lesioning of the globus pallidus to treat Parkinson's disease . Multiple intraoperative microelectrode recording/stimulating tracks are s earched and assessed for neuronal activity, presence of tremor cells, visua l responses, and responses to kinesthetic input. These physiological data a re then correlated with atlas-based anatomic data to approximate electrode location. On the basis of these physiological properties, one or more track s are selected for lesioning. This study analyzes the track physiological f actors that seem most significant in determining the microelectrode recordi ng track(s) that will be chosen for pallidal lesioning. METHODS: Thirty-six patients with Parkinson's disease underwent microelectr ode-guided pallidotomy. Between one and five microelectrode recording track s were made per patient. Usually, one (n = 23) or two (n = 12) of these tra cks were lesioned. Electrode positions in the x (mediolateral) and y (anter oposterior) axes were recorded and related to track neurophysiological find ings and final lesion location. The stereotactic location and sequence of m icroelectrode tracks were recorded and plotted to illustrate individual sea rch patterns. These patterns were then compared with those noted in other p atients. Neurophysiological data obtained from recording tracks were analyz ed. A retrospective analysis of track electrophysiology was performed to de termine the track characteristics that seemed most important in the surgeon 's choice of the track to lesion. Track physiological properties included g eneral cell spike amplitude, tremor synchronous neuronal firing, kinestheti cally responsive neuronal firing, and optic track responses (either phosphe nes reported by the patient during track microstimulation or neuronal firin g in response to light stimulus into the patient's eyes). Orthogonally corr ected postoperative magnetic resonance images were used to confirm the anat omic lesion locations. RESULTS: In patients who had a single mapped track lesioned, specific track electrophysiological characteristics identified the track that would be le sioned most of the time (20 of 24 patients). Tracks that exhibited a combin ation of tremor synchronous firing, joint kinesthesia, and visual responsiv ity were lesioned 17 (85%) of 20 times. Analysis of intraoperative electrod e movement in the x and y axes indicated a significant subset of moves but did not result in microelectrode positioning closer to the subsequently les ioned track. Accuracy of initial electrode movement in the x and y axes was most highly correlated with a measure of first-track electrophysiological activity. The number of microelectrode recording tracks did not correlate w ith clinical outcome. Anatomic analysis, using postoperative magnetic reson ance imaging, revealed that all lesions were placed in the globus pallidus. Most patients (35 of 36) improved after surgery. CONCLUSION: The level of electrophysiological activity in the first track w as the best predictive factor in determining whether the next microelectrod e move would be closer to the ultimately lesioned track. The analysis of el ectrode track location and neurophysiological properties yields useful info rmation regarding the effectiveness of microelectrode searching in the rand y axes. Within an institution, the application of this modeling method may increase the efficiency of the microelectrode refinement process.