Simon Parkin

Hardware-Related problems of deep brain stimulation

Deep brain stimulation for the alleviation of movement disorders and pain is now an established therapy. However, very little has been published on the topic of hardware failure in the treatment of such conditions irrespective of clinical outcome. Such device‐related problems lead to significant patient morbidity and increased cost of therapy in the form of prolonged antibiotics, in‐patient hospitalization, repeat surgery, and device replacement. We report a prospective review of our experience at the Radcliffe Infirmary Oxford from the period of April 1998 to March 2001. Overall there is a 20% rate of hardware‐related problems in this series, which falls between the 7% and 65% rates reported by other groups. The majority of these failures occurred early on in the series, and numbers declined with experience. Some of the problems may be idiosyncratic to the methodology of individual groups.

Unilateral and bilateral pallidotomy for idiopathic Parkinson's disease: a case series of 115 patients.

Lesioning of the internal pallidum is known to improve the symptoms of idiopathic Parkinsons disease (PD) and alleviate dyskinesia and motor fluctuations related to levodopa therapy. The benefit obtained contralateral to a single lesion is insufficient in some cases when symptoms are bilaterally disabling. However, reports of unacceptably high rates of adverse effects after bilateral pallidotomy have limited its use in such cases. We report on the outcome of unilateral (UPVP) and bilateral (BPVP) posteroventral pallidotomy in a consecutive case series of 115 patients with PD in the United Kingdom and Australia. After 3 months, UPVP resulted in a 27% reduction in the off medication Part III (motor) Unified Parkinsons Disease Rating Scale score and abolition of dyskinesia in 40% of cases. For BPVP, these figures were increased to 31% and 63%, respectively. Follow‐up of a smaller group to 12 months found the motor scores to be worsening but benefit to dyskinesia and activities of daily living was maintained. Speech was adversely affected after BPVP, although the change was small in most cases. Unilateral and bilateral pallidotomy can be performed safely without microelectrode localisation. Bilateral pallidotomy appears to be more effective, particularly in reducing dyskinesia; in our experience, the side effects have not been as high as reported by other groups.

Involvement of the medial pallidum in focal myoclonic dystonia: A clinical and neurophysiological case study.

We successfully treated a patient with familial myoclonic dystonia (FMD), which primarily affected his neck muscles, with bilateral deep brain stimulation (DBS) to the medial pallidum, and investigated the role of the medial pallidum in FMD. A patient with FMD underwent bilateral implantation of DBS electrodes during which field potentials (FPs) in the medial pallidum and electromyograms (EMGs) from the affected neck muscles were recorded. The effects of high‐frequency DBS to the medial pallidum on the FMD were also assessed by recording EMGs during and immediately after implantation, as well as 6 days and 8 weeks postoperatively. During spontaneous myoclonic episodes, increased FPs oscillating at 4 and 8 Hz were recorded from the medial pallidum; these correlated strongly with phasic EMG activity at the same frequencies in the contralateral affected muscles. The EMG activity was suppressed by stimulating the contralateral medial pallidum at 100 Hz during the operation and continuous bilateral DBS from an implanted stimulator abolished myoclonic activity even more effectively postoperatively. The phasic pallidal activity correlated with and led the myoclonic muscle activity, and the myoclonus was suppressed by bilateral pallidal DBS, suggesting that the medial pallidum was involved in the generation of the myoclonic activity. High‐frequency DBS may suppress the myoclonus by desynchronising abnormal pallidal oscillations. This case study has significant clinical implications, because at present, there is no effective treatment for focal myoclonic dystonia.

Executive cognitive deficits in primary dystonia.

Primary dystonia is a disorder of movement for which no consistent pathophysiology has been identified; in the absence of evidence to the contrary, it is assumed to be cognitively benign. We have studied a clinically heterogeneous group of 14 patients with primary dystonia on a battery of neuropsychological tests. Despite well‐preserved speed of information processing, language, spatial, memory and general intellectual skills relative to normal controls, we have identified a constellation of attentional–executive cognitive deficits on the Cambridge Neuropsychological Test Automated Battery (CANTAB). Specifically, patients demonstrated significant difficulties negotiating the extra‐dimensional set‐shifting phase of the IED task. The implications of these findings for the pathophysiology of primary dystonia are discussed. This is, to the best of our knowledge, the first report of a significant cognitive deficit in patients with primary dystonia.

Bilateral internal globus pallidus stimulation for the treatment of spasmodic torticollis.

Three patients with spasmodic torticollis (ST) obtained substantial benefit from bilateral globus pallidus internus (GPi) stimulation. Progressive improvement in ST occurred over several months but residual cervical dystonia remained. These results corroborate those obtained by Krauss et al. on three patients with ST.

Electrophysiological confirmation of the zona incerta as a target for surgical treatment of disabling involuntary arm movements in multiple sclerosis: use of local field potentials

Lesioning or chronic deep brain stimulation (DBS) of the nucleus ventralis intermedius results in abolition of tremor in the contralateral limbs in Parkinsons disease (PD) and also in essential tremor. Recently, chronic DBS of the subthalamic nucleus has also proved to be very effective in reducing contralateral limb tremor in PD. These targets have been less effective in controlling the complex limb tremor often seen in multiple sclerosis (MS). Consequently, other targets have been sought in cases of MS with tremor. We describe a patient with MS with disabling proximal and distal involuntary arm movements in whom we were able to obtain sustained control of contralateral arm tremor and achieve functional improvement of the affected arm by chronic DBS of the region of the zona incerta. We also highlight the important role played by local field potentials recorded from the brain, with simultaneous recording of corresponding EMGs, in target localisation.

Localisation of the subthalamic nucleus using Radionics Image Fusion and Stereoplan combined with field potential recording. A technical note.

Subthalamic nucleus stimulation is an effective therapy for alleviating parkinsonian tremor, rigidity and bradykinesia. Although microelectrode recording is said to be essential for accurate targeting, this often prolongs the operation and the multiple recording tracts required may increase the incidence of complications, particularly haemorrhage. We describe a technique for implantation of deep brain electrodes in the subthalamic nucleus using MRI/CT fusion for anatomical localisation followed by bipolar recording of focal field potentials via the implanted stimulating electrode for neurophysiological confirmation of the stimulation site. The technique is effective, safe and requires much less time, and can be used as an alternative method to microelectrode recording.

Targeting the subthalamic nucleus.

The small size and surrounding neuronal structures and fibre tracts make the STN a difficult stereotactic target. In this article we present the technique used by us to target the STN. Our combined experience from two centres comprises 18 lesions and 27 stimulator implants in the STN. Our criteria for patient selection and the use of MRI, frame-on CT and volumetric image fusion are presented. The role of a movement disorder specialist neurologist in the operating theatre, local field potential recording, impedance monitoring, macrostimulation, post-operative CT/MRI and test stimulation are detailed.

Lesioning the subthalamic nucleus in the treatment of Parkinson's disease.

Ever since it was demonstrated about twenty years ago by two independent groups (Aziz et al. and Bergman et al.) that the cardinal clinical features of MPTP-induced Parkinson’s disease (PD) in non-human primate models can be alleviated by lesions of the subthalamic nucleus (STN), this structure has been the focus of interest for functional neurosurgeons involved in the treatment of PD. Initially lesioning and later chronic high frequency stimulation of the STN has become the standard surgical target of akinetic PD. In this brief report we present our experience with 14 STN lesions (8 unilateral and 3 bilateral) confirmed by post-operative imaging. We found significant improvement in OFF rigidity and in ON tremor following unilateral lesions. The major complications were speech disturbance and L-Dopa resistant limb dystonia. Functional disability scores showed inconsistent reduction. There was insufficient data to comment on the significance of bilateral lesions; however, there was a similar pattern of improvement in tremor and speech disturbance. In addition, there was worsening of gait. We comment on the lower degree of improvement in motor scores in our series compared to the few others in recent literature and stress that even in these studies the UPDRS benefits did not translate directly into functional benefit for the patients.

Camptocormia treated with bilateral pallidal stimulation: case report.

The authors report the neurological, neurophysiological, and neuropsychological effects of using chronic bilateral pallidal high-frequency deep brain stimulation (DBS) in a case of disabling camptocormia. Deep brain stimulation electrodes were implanted stereotactically to target the globus pallidus internus (GPi) bilaterally. Local field potentials (FPs) were recorded using the DBS electrodes and concurrent abdominal flexor electromyography (EMG) potentials during camptocormic episodes. Videotaped assessments of the movement disorder and neuropsychological evaluation before implantation and at 6 months after initiation of pallidal stimulation were recorded. There was significant functional improvement following chronic pallidal stimulation, and some improvement was noted in neuropsychological scores. The GPi FPs showed temporal correlation with EMG-recorded rectus abdominis potentials. There were no treatment-related adverse effects. The authors have found that chronic pallidal stimulation was safe and offered functional benefit in this severely disabling condition. The physiological studies may help further the understanding of the pathophysiology of this rare entity.