Relationship of lesion location to clinical outcome following microelectrode-guided pallidotomy for Parkinson's disease

The purpose of this study was to examine the relationship between lesion lo cation and clinical outcome following globus pallidus internus (GPi) pallid otomy for advanced Parkinson's disease. Thirty-three patients were prospect ively studied with extensive neurological examinations before and at 6 and 12 months following microelectrode-guided pallidotomy, Lesion location was characterized using volumetric MRI, The position of lesions within the post eroventral region of the GPi was measured, from anteromedial to posterolate ral along an axis parallel to the internal capsule, To relate lesion positi on to clinical outcome, hierarchical multiple regression analysis was used. The variance in outcome measures that was related to preoperative scores a nd lesion volume was first calculated, and then the remaining variance attr ibutable to lesion location was determined. Lesion location along the anter omedial-to-posterolateral axis within the GPi influenced the variance in to tal score on the Unified Parkinson's Disease Rating Scale in the postoperat ive 'off' period, and in 'on' period dyskinesia scores. Within the posterov entral GPi, anteromedial lesions were associated with greater improvement i n 'off' period contralateral rigidity and 'on' period dyskinesia, whereas m ore centrally located lesions correlated with better postoperative scores o f contralateral akinesia and postural instability/gait disturbance. Improve ment in contralateral tremor was weakly related to lesion location, being g reater with posterolateral lesions. We conclude that improvement in specifi c motor signs in Parkinson's disease following pallidotomy is related to le sion position within the posteroventral GPi, These findings are consistent with the known segregated but parallel organization of specific motor circu its in the basal ganglia, and may explain the variability in clinical outco me after pallidotomy and therefore have important therapeutic implications.