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Biomedical subjects

Tipu Z Aziz

Publications and source records attributed to Tipu Z Aziz.

At least 37 records · Page 2Linked to original sources
PubMed2005

Deep brain stimulation for movement disorders and pain.

Deep brain stimulation (DBS) is an expanding field within neurosurgery. With many neurosurgeons performing relatively small numbers of these procedures, detailed descriptions of the technical aspects and nuances of DBS may be worthwhile. We describe our technique for DBS, based on over 300 procedures. This methodology continues to evolve and is refined according to our own experience, our observations of others, technological innovations, and information derived from the neurosurgical literature. The indications for DBS in our service are outlined, the anatomical targets described, and the anaesthetic and surgical aspects detailed.

Deep Brain Stimulation↗
PubMed2005

Thalamotomy versus thalamic stimulation for multiple sclerosis tremor.

Disabling intractable tremor occurs frequently in patients with multiple sclerosis (MS). There is currently no effective medical treatment available, and the results of surgical intervention have been variable. Thalamotomy has been the mainstay of neurosurgical therapy for intractable MS tremor, however the popularisation of deep brain stimulation (DBS) has led to the adoption of chronic thalamic stimulation in an attempt to ameliorate this condition. With the goal of examining the relative efficacy and adverse effects of these two surgical strategies, we studied twenty carefully selected patients with intractable MS tremor. Thalamotomy was performed in 10 patients, with chronic DBS administered to the remaining 10. Both thalamotomy and thalamic stimulation produced improvements in postural and intention tremor. The mean improvement in postural tremor at 16.2 months following surgery was 78%, compared with a 64% improvement after thalamic stimulation (14.6 month follow-up) (P > 0.05). Intention tremor improved by 72% in the group undergoing thalamotomy, a significantly larger gain than the 36% tremor reduction following DBS (P < 0.05). Early postoperative complications were common in both groups. Permanent complications related to surgery occurred in four patients overall. Following thalamotomy, long-term adverse effects were observed in three patients (30%), and comprised hemiparesis and seizures. Only one patient in the thalamic stimulation group experienced a permanent deficit (monoparesis). We conclude that thalamotomy is a more efficacious surgical treatment for intractable MS tremor, however the higher incidence of persistent neurological deficits in patients receiving lesional surgery may support the use of DBS as the preferred surgical strategy.

Adult↗
PubMed2005

Deep brain stimulation for pain relief: a meta-analysis.

Deep brain stimulation (DBS) has been used to treat intractable pain for over 50 years. Variations in targets and surgical technique complicate the interpretation of many studies. To better understand its efficacy, we performed a meta-analysis of DBS for pain relief. MEDLINE (1966 to February 2003) and EMBASE (1980 to January 2003) databases were searched using key words deep brain stimulation, sensory thalamus, periventricular gray and pain. Inclusion criteria were based on patient characteristics and protocol clarity. Six studies (between 1977-1997) fitting the criteria were identified. Stimulation sites included the periventricular/periaqueductal grey matter (PVG/PAG), internal capsule (IC), and sensory thalamus (ST). The long-term pain alleviation rate was highest with DBS of the PVG/PAG (79%), or the PVG/PAG plus sensory thalamus/internal capsule (87%). Stimulation of the sensory thalamus alone was less effective (58% long-term success) (p < 0.05). DBS was more effective for nociceptive than deafferentation pain (63% vs 47% long-term success; p < 0.01). Long-term success was attained in over 80% of patients with intractable low back pain (failed back surgery) following successful trial stimulation. Trial stimulation was successful in approximately 50% of those with post-stroke pain, and 58% of patients permanently implanted achieved ongoing pain relief. Higher rates of success were seen with phantom limb pain and neuropathies. We conclude that DBS is frequently effective when used in well-selected patients. Neuroimaging and neuromodulation technology advances complicate the application of these results to modern practice. Ongoing investigations should shed further light on this complex clinical conundrum.

Animals↗
PubMed2005

Connectivity of the human periventricular-periaqueductal gray region.

OBJECT: The periventricular gray (PVG) zone and its continuation, the periaqueductal gray (PAG) substance, have been targets for deep brain stimulation (DBS) in the alleviation of intractable pain for longer than two decades. Nevertheless, the anatomical connectivity of this region has been fairly poorly defined. The effects of DBS in this region are probably related to the release of endogenous endorphins, but until the connectivity of this region is better understood the mechanisms will remain unclear. METHODS: Diffusion tractography was used to trace the pathways of the PVG-PAG region in seven healthy human volunteers. Images were acquired with the aid of a 1.5-tesla magnetic resonance imaging system. The region of interest was located just lateral to the posterior commissure and extended caudally to the level of the superior colliculus. Probabilistic diffusion tractography was performed from each voxel in each patient's PVG-PAG region. The PVG-PAG region was found to yield descending projections to the spinal cord and cerebellum. Ascending projections to the thalamus and frontal lobes were also observed. CONCLUSIONS: These findings suggest that the PVG-PAG region may modulate pain by two mechanisms: one involving the antinociceptive system in the spinal cord and the other involving influences on the central pain network.

Afferent Pathways↗
PubMed2005

Intraoperative monitoring of motor symptoms using surface electromyography during stereotactic surgery for movement disorders.

The authors present practical evidence for the usefulness of intraoperative monitoring with surface electromyograms (sEMGs) from the affected muscles to assist electrode implantation and lesioning in patients with movement disorders. In 22 consecutive patients with various movement disorders, sEMGs were monitored in selected muscles during stereotactic surgery that involved either lesioning or electrode implantation. The electromyograms related to major motor symptoms such as tremor, rigidity, myoclonus, dystonia, and chorea were monitored and characterized on-line by both amplitude and frequency. Major motor symptoms were revealed by sEMGs recorded from the affected muscles. Tremor manifested as highly rhythmic bursts with a narrow frequency band; dyskinesias and chorea appeared as irregularly repeated bursts within a broad frequency range of 1 to 5 Hz; and rigidity and dystonia appeared as sustained high-frequency activity and co-contraction between antagonist muscles. The results suggest that intraoperative monitoring of sEMGs could help to functionally refine and confirm target localization. Surface EMGs could be used (1) as reference signals of the motor symptoms so that other signals, such as the oscillatory local field potentials simultaneously recorded via the implanted electrodes, could be correlated with the sEMGs and used to fine-tune or confirm the target localization; (2) to quantify the effects of acute electrical stimulation on the motor symptoms; and (3) to sensitively detect unwanted capsular responses induced by direct stimulation of the internal capsule. The authors conclude that intraoperative monitoring of sEMGs of the affected muscles of patients with movement disorders during stereotactic surgery provides sensitive and quantitative information that can contribute to improved electrode or lesion placement.

Electric Stimulation↗
PubMed2004

Pedunculopontine nucleus stimulation improves akinesia in a Parkinsonian monkey.

We have studied the effects of stimulating the pedunculopontine nuclei through a fully implanted macroelectrode with a s.c. implantable pulse generator whose parameters can be programmed telemetrically, in a macaque before and after inducing Parkinsonian akinesia with MPTP. Our results show that in the normal monkey high frequency stimulation of the pedunculopontine nuclei reduces motor activity while low frequency stimulation increases it significantly over baseline. After making the monkey Parkinsonian with MPTP, unilateral low frequency stimulation of the pedunculopontine nuclei led to significant increases in activity. These results suggest that pedunculopontine nuclei stimulation could be clinically effective in treating advanced Parkinson's disease and other akinetic disorders.

Animals↗
PubMed2004

Extracting burst and tonic components from surface electromyograms in dystonia using adaptive wavelet shrinkage.

The compound surface electromyograms (EMGs) recorded from patients with dystonia commonly contains superimposed bursting and tonic activity representing various motor symptoms. It is desirable to differentially extract them from the compound EMGs so that different symptoms can be more specifically investigated and different mechanisms revealed. A non-linear denoising approach based on wavelet transformation was investigated by applying soft thresholding to the wavelet coefficients. Thresholds were determined according to three different principles and two models. Different techniques for wavelet shrinkage were investigated for separating burst and tonic activity in the compound EMGs. The combination of Stein's unbiased risk estimate principle with a non-white noise model proved optimal for separating burst and tonic activity. These turned out to be exponentially related; and the temporal relationships between antagonist muscle contractions could now be seen clearly. We conclude that adaptive soft-thresholding wavelet shrinkage provides effective separation of burst and tonic activity in the compound EMG in dystonia. This separation should improve our understanding of the pathophysiology of dystonia.

Action Potentials↗
PubMed2004

Optimising coherence estimation to assess the functional correlation of tremor-related activity between the subthalamic nucleus and the forearm muscles.

Application of coherence estimation needs not only to correctly estimate coherence values but also to efficiently test the statistical significance of the estimates. In the present report, we have explained the approach of optimising a coherence estimator by restricting its normalised bias error and random error. In addition to the commonly used independence threshold, two more tests based on the probability of detection and the exact confidence interval have been proposed for detecting the significance of the coherence estimates. All three methods have been used to evaluate the significant functional correlation between oscillatory field potentials (FPs) in the subthalamic nucleus (STN) and the surface electromyogram (EMG) of the forearm muscles during tremor in Parkinson's disease.

Action Potentials↗
PubMed2002

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.

Abdominal Muscles↗
PubMed2002

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.

Adult↗
PubMed2002

Brainstem motor loops in the control of movement.

In recent years, the role of the area around the upper brainstem, particularly the pedunculopontine (PPN) region and the zona incerta (ZI), in the initiation and control of movement has generated much clinical interest. Using electrophysiological and pharmacological methods, we have further explored these structures and their influence in motor control in the nonhuman primate and in patients with proximal tremor. We have found that lesioning the PPN and electrical stimulation at high frequencies of the PPN region in the normal-behaving primate induces akinesia, and low frequency stimulation can induce tremor. In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) -treated parkinsonian primate model, bicuculline, a gamma-aminobutyric acid antagonist, can alleviate akinesia when infused into the PPN region. Further studies will elucidate the possible clinical implications of these observations. The ZI has reciprocal connections with several cortical areas, the upper brainstem, cerebellum, and thalamus. We have found that chronic, high-frequency deep brain stimulation of the ZI suppresses proximal limb tremor. Field potential recordings from the ZI show significant coherence with concurrent proximal muscle electromyograms. This finding has potential clinical relevance as proximal tremor generally does not respond well to thalamic surgery and may be severely disabling.

Animals↗
PubMed2002

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 Parkinson's 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 Parkinson's 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.

Aged↗
PubMed2002

Deep brain stimulation of the pedunculopontine region in the normal non-human primate.

Lesions in the pedunculopontine nucleus (PPN) cause akinesia. The PPN degenerates in Parkinson's disease. Stimulation of the PPN region induces stepping movements in rats and cats. These findings suggest that the PPN may play an important role in akines ia and that stimulating it may alleviate akinesia.Therefore, we have stereotactically implanted a macroelectrode in the left PPN region in a normal macaque to investigate the effects of deep brain stimulation at different frequencies. Motor activity was recorded with an infra-red counter and behaviour videotaped. At frequencies above 45 Hz there was significantly more severe akinesia than at lower frequencies (paired t -test, n=15, P<0.005). At 100 Hz, there was gross impairment of postural control. At low frequencies (5-30 Hz), stimulation induced a 5-Hz tremor in the right arm. We conclude that stimulating the PPN region at high frequency causes akinesia, whereas low frequencies induce some positive motor effects.

Animals↗
PubMed2002

Global attentional-executive sequelae following surgical lesions to globus pallidus interna.

It has been demonstrated that selective unilateral surgical ablation of posteroventral globus pallidus interna relieves the movement disorders associated with advanced Parkinson's disease, without necessarily incurring the executive cognitive sequelae that have been observed following gross pathological lesions to this brain region. This finding is consistent with established theory that underlying neuronal circuitry is functionally segregated into parallel cortico-striatal-pallidal-thalamo-cortical 'loops'. We have studied a series of 12 patients with advanced Parkinson's disease at baseline, and then following bilateral pallidotomy, with a battery of neuropsychological tests including the Cambridge Neuro psychological Test Automated Battery. We identified a selective and universal loss of individual patients' ability to shift attention to novel dimensions in a test of abstract rule-learning following surgery, which was not reliably associated with any other change in cognition, personality, mood or medication. This finding is rare in its specificity and has implications for theoretical models of the functional architecture and pathophysiology of the globus pallidus, and the clinical practice of pallidotomy.

Adult↗
PubMed2002

Reversal of akinesia in experimental parkinsonism by GABA antagonist microinjections in the pedunculopontine nucleus.

Recent studies, mainly in animals, have shown that the pedunculopontine nucleus (PPN) in the upper brainstem has extensive connections with several motor centres in the CNS. This structure has also been implicated in the akinesia seen in patients with Parkinson's disease. Here we demonstrate that microinjection of gamma-aminobutyric acid (GABA) receptor A antagonist substance, bicuculline, into the PPN of non-human primates (n = 2) rendered parkinsonian with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) results in significant improvement of akinesia. The effect of bicuculline microinjection in the PPN matches that of oral administration of L-dopa. This finding opens up new possibilities in the management of akinesia, the most intractable symptom of advanced Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2002

Camptocormia treated with bilateral pallidal stimulation.

The authors report the neurological, neurophysiological, and neuropsychological effects of using long-term 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 evaluations of the patient before implantation and 6 months after initiation of pallidal stimulation were recorded. There was significant functional improvement following long-term pallidal stimulation, and some improvement was noted in neuropsychological scores. A temporal correlation between the GPi FPs and EMG-recorded rectus abdominis potentials was evident. There were no treatment-related adverse effects. The authors have found that long-term pallidal stimulation was safe and offered functional benefit to a patient with this severely disabling condition. The physiological studies may help further the understanding of the pathophysiology of this rare entity.

Adult↗