Reappraisal of the anatomical landmarks of motor and premotor cortical regions for image-guided brain navigation in TMS practice.

Image-guided navigation systems dedicated to transcranial magnetic stimulation (TMS) have been recently developed and offer the possibility to visualize directly the anatomical structure to be stimulated. Performing navigated TMS requires a perfect knowledge of cortical anatomy, which is very variable between subjects. This study aimed at providing a detailed description of sulcal and gyral anatomy of motor cortical regions with special interest to the inter-individual variability of sulci. We attempted to identify the most stable structures, which can serve as anatomical landmarks for motor cortex mapping in navigated TMS practice. We analyzed the 3D reconstruction of 50 consecutive healthy adult brains (100 hemispheres). Different variants were identified regarding sulcal morphology, but several anatomical structures were found to be remarkably stable (four on dorsoventral axis and five on rostrocaudal axis). These landmarks were used to define a grid of 12 squares, which covered motor cortical regions. This grid was used to perform motor cortical mapping with navigated TMS in 12 healthy subjects from our cohort. The stereotactic coordinates (x-y-z) of the center of each of the 12 squares of the mapping grid were expressed into the standard Talairach space to determine the corresponding functional areas. We found that the regions whose stimulation produced almost constantly motor evoked potentials mainly correspond to the primary motor cortex, with rostral extension to premotor cortex and caudal extension to posterior parietal cortex. Our anatomy-based approach should facilitate the expression and the comparison of the results obtained in motor mapping studies using navigated TMS.

Outcome of bilateral subthalamic nucleus stimulation in the treatment of Parkinson's disease: correlation with intra-operative multi-unit recordings but not with the type of anaesthesia.

BACKGROUND: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) gained general acceptance in the treatment of Parkinson's disease (PD). OBJECTIVE: To study the clinical outcome and the predicting factors of efficacy of chronic STN stimulation, while DBS electrodes were implanted under local or general anaesthesia with intra-operative electrophysiological guidance based on multi-unit recordings. METHODS: We included a large single-centre cohort of 54 patients with advanced PD (mean age: 59 years; disease duration: 14 years). Clinical evaluation was performed by the Unified Parkinson's Disease Rating Scale (UPDRS) before and 1 year after surgical placement of DBS electrodes. RESULTS: In the on-stimulation and off-medication condition, the UPDRS part III score was reduced by 56% compared to the off-stimulation condition or pre-operative off-drug score. In the on-stimulation and on-medication condition, this score was reduced by 73%. The severity of motor fluctuations and dyskinesia (UPDRS part IV) and the activities of daily living (UPDRS part II) were reduced by 65 and 80%, respectively, in the on-stimulation/on-medication condition compared to the pre-operative baseline. The daily dose of antiparkinsonian treatment was diminished by 72%. Among the various pre- and intra-operative data, the most important predictive factor for clinical efficacy of STN stimulation was the length of hyperactivity along the best track observed in intra-operative multi-unit recordings. Other predictive factors included age, disease duration and pre-operative levodopa responsiveness or baseline off-drug values of the Hoehn and Yahr and UPDRS part III scores. In contrast, the type of anaesthesia (local vs. general) did not significantly influence the clinical outcome. CONCLUSION: The present results are in the average of previously published results, but they have been obtained from a large single-centre cohort of patients with important reductions in the daily dose of antiparkinsonian drugs. This study confirmed the efficacy of the STN-DBS technique and emphasized the value of an original intra-operative electrophysiological approach based on multi-unit and not single-unit quantified recordings. This method allows DBS electrode implantation to be safely performed under general anaesthesia without lessening the rate of efficacy of the procedure.

Chronic motor cortex stimulation in the treatment of central and neuropathic pain. Correlations between clinical, electrophysiological and anatomical data.

Thirty-two patients with refractory central and neuropathic pain of peripheral origin were treated by chronic stimulation of the motor cortex between May 1993 and January 1997. The mean follow-up was 27.3 months. The first 24 patients were operated according to the technique described by Tsubokawa. The last 13 cases (eight new patients and five reinterventions) were operated by a technique including localisation by superficial CT reconstruction of the central region and neuronavigator guidance. The position of the central sulcus was confirmed by the use of intraoperative somatosensory evoked potentials. The somatotopic organisation of the motor cortex was established peroperatively by studying the motor responses at stimulation of the motor cortex through the dura. Ten of the 13 patients with central pain (77%) and ten of the 12 patients with neuropathic facial pain had experienced substantial pain relief (75%). One of the three patients with post-paraplegia pain was clearly improved. A satisfactory result was obtained in one patient with pain related to plexus avulsion and in one patient with pain related to intercostal herpes zooster. None of the patients developed epileptic seizures. The position of the stimulating poles effective on pain corresponded to the somatotopic representation of the motor cortex. The neuronavigator localisation and guidance technique proved to be most useful identifying the appropriate portion of the motor gyrus. It also allowed the establishment of reliable correlations between electrophysiological-clinical and anatomical data which may be used to improve the clinical results and possibly to extend the indications of this technique.