PubMed Health⌕ Search

Biomedical subjects

Clement Hamani

Publications and source records attributed to Clement Hamani.

At least 19 recordsLinked to original sources
PubMed2006

Saccade-related potentials recorded from human subthalamic nucleus.

OBJECTIVE: To investigate an ocular motor role for the STN in Parkinson's disease (PD) patients. METHODS: Potentials were recorded from deep brain stimulation (DBS) electrodes implanted in the vicinity of STN in five PD patients, while patients simultaneously performed visually cued saccades, self-paced saccades and in two patients self-paced wrist extensions. RESULTS: Premovement potentials related to visually cued saccades were found in 4/5 patients and 56% (5/9) of potentials showed phase reversal indicating a local generator. Onsets of these potentials began closer to saccade initiation from STN contacts (0.88+/-0.30s) than thalamic ones (1.39+/-0.28 s). Self-paced saccade-related potentials were found in 4/4 patients. Self-paced saccade potential onsets (1.82+/-0.88 s) were not different from self-paced wrist extension onsets (1.27+/-0.98 s), suggesting a non-specific mechanism could be responsible for both potentials. 50% (3/6) of potentials to self-paced saccades and 66% (2/3) of potentials to self-paced wrist extensions showed phase reversal. Potentials could be found either ipsilaterally or contralaterally with respect to saccade direction. CONCLUSIONS: These subcortical premovement potentials to saccades are similar to Bereitschaftspotentials and contingent negative variations to limb movements recorded in cortical and subcortical regions. SIGNIFICANCE: These studies further support a role of STN in ocular motor control and suggest a common mechanism of motor preparation for both eye and limb movements in the basal ganglia.

Adult↗
PubMed2006

Hardware-related complications of deep brain stimulation: a review of the published literature.

Hardware-related complications have been commonly described after deep brain stimulation. We searched the PubMed database using the key words 'adverse effects' and 'deep brain stimulation'. Out of 254 studies, we identified 10 articles that primarily addressed morbidity and hardware-related adverse effects in 922 patients. The most commonly reported hardware-related complications were infections (6.1% of the patients), migration or misplacement of the leads (5.1% of the patients), lead fractures (5.0% of the patients), and skin erosion (1.3% of the patients). Refinements in surgical technique, technological improvements, and a greater experience with the procedures will likely decrease the incidence of hardware-related side effects in the future.

Deep Brain Stimulation↗
PubMed2006

Deep brain stimulation for chronic neuropathic pain: long-term outcome and the incidence of insertional effect.

We conducted a retrospective analysis of long-term results of deep brain stimulation (DBS) for the treatment of neuropathic pain. Twenty-one patients had electrodes implanted in the ventrocaudalis thalamic nucleus (Vc) (n=13) or in both Vc and periaqueductal/periventricular gray matter (PAG/PVG) (n=8). After insertion of the electrodes, 9 patients (43%) had a substantial reduction in pain scores in the absence of stimulation (insertional effect). The effects of stimulation were studied right after surgery or upon return of the patients' pain after electrode insertion (stimulation trials). Patients with a greater than 50% reduction in pain scores were implanted with a pulse generator (IPG). Of interest, patients who had an insertional effect had a trend towards a successful stimulation trial (p=0.08). Overall, 13 of the 21 patients operated (62%) had a successful stimulation trial and received an IPG (12 with electrodes in Vc and one in both Vc and PAG/PVG). Seven patients (33%) did not benefit from stimulation and had the electrodes removed. One patient experienced a prolonged insertional effect and has not required stimulation. Of the 13 patients that received an IPG, 8 discontinued stimulation during the first year of treatment. Only 5 patients maintained long-term benefit (4 with stimulation in Vc and one in both Vc and PAG/PVG). The relatively low efficacy of DBS for the treatment of neuropathic pain stresses the need for further investigation and the exploration of new surgical targets.

Adult↗
PubMed2006

The motor thalamus in neurosurgery.

The motor thalamus is an important target for the treatment of tremor. It receives afferents from the cerebellum, globus pallidus internus, and substantia nigra and projects mainly to the motor cortex, premotor cortex, and supplementary motor area. Various nomenclatures have been proposed to subdivide the motor thalamus, none of which are universally accepted. Both thalamic lesions and high-frequency stimulation ameliorate tremor in diverse pathological conditions. Modern neurophysiological techniques have allowed the recording of the activity of thalamic neurons in patients with different clinical conditions. This has provided a better understanding of the functions of the motor thalamus in humans. The aim of the present article is to briefly review the major anatomic and physiological aspects of the motor thalamus as well as the electrophysiological findings described in humans undergoing surgical procedures.

Electrophysiology↗
PubMed2006

Neural stimulation for Parkinson's disease: current therapies and future directions.

Neural stimulation has rapidly become an integral tool in the treatment of Parkinson's disease and other movement disorders. Today it serves as an important adjunct to medical therapy that continues to gain applicability to patients in whom the disease has progressed significantly. Studies have demonstrated efficacy in several deep-brain targets, with prolonged benefit exceeding 5-year follow-up times. Continuing study is teaching us more about the mechanism of deep-brain stimulation effect. New targets, which may treat the disease more successfully, are being examined. In this review, the history of deep-brain stimulation, the rationale for the known targets of stimulation; the clinical evidence demonstrating their benefit and, finally, future perspectives on new treatments that are being investigated and may have an impact on the field are discussed.

Brain↗
PubMed2005

Deep brain stimulation for treatment-resistant depression.

Treatment-resistant depression is a severely disabling disorder with no proven treatment options once multiple medications, psychotherapy, and electroconvulsive therapy have failed. Based on our preliminary observation that the subgenual cingulate region (Brodmann area 25) is metabolically overactive in treatment-resistant depression, we studied whether the application of chronic deep brain stimulation to modulate BA25 could reduce this elevated activity and produce clinical benefit in six patients with refractory depression. Chronic stimulation of white matter tracts adjacent to the subgenual cingulate gyrus was associated with a striking and sustained remission of depression in four of six patients. Antidepressant effects were associated with a marked reduction in local cerebral blood flow as well as changes in downstream limbic and cortical sites, measured using positron emission tomography. These results suggest that disrupting focal pathological activity in limbic-cortical circuits using electrical stimulation of the subgenual cingulate white matter can effectively reverse symptoms in otherwise treatment-resistant depression.

Adult↗
PubMed2005

Comparison of 2-dimensional magnetic resonance imaging and 3-planar reconstruction methods for targeting the subthalamic nucleus in Parkinson disease.

OBJECTIVE: The study aims to compare 2-dimensional (2D) and 3-planar (3P) reconstruction magnetic resonance imaging (MRI) methods of targeting the optimal region of the subthalamic nucleus (STN) for chronic stimulation in patients with Parkinson disease. METHODS: We studied 14 patients with Parkinson disease treated with bilateral STN deep brain stimulation (DBS) (28 STN targets). Electrode implantation was based on direct and indirect targeting based upon the position of the anterior and posterior commissures using 2D MRI, with selection of the final target based on microelectrode recording. Optimal settings, including the contacts used, were determined during the clinical follow-up. The position of the best contact was defined with postoperative MRI. Optimal contact position was compared to targets calculated by the direct method from the preoperative 2D MRI and 3P reconstruction. Optimal contact position was also compared to the indirect targets calculated from the preoperative 2D MRI and 3P reconstruction. The distance between the targets and the position of the best contact were calculated. RESULTS: The mean improvement in OFF-period Unified Parkinson Disease Rating Scale III subscores with STN DBS was 52%. The mean distance between the optimal contact position and the direct target was 4.66 mm (SD = 1.33) using the 2D MRI and 3.49 mm (SD = 1.29) using the 3P reconstruction (t test, P < .001). The mean distance between the optimal contact and the indirect target was 3.42 mm (SD = 1.34) using the 2D MRI and 2.61 mm (SD = 0.97; t test, P = .001) using the 3P reconstruction. The variance of the direct target was less using the 3P reconstruction than using the 2D MRI (F test, P = .002), indicating greater precision. Similarly, the variance of the indirect target using the 3P reconstruction was less than using the 2D MRI (F test, P = .012). CONCLUSION: Indirect and direct targets chosen using 3P reconstruction more closely approximate the position of the clinically optimal contact than targets chosen using 2D MRI.

Deep Brain Stimulation↗
PubMed2005

Correspondence of microelectrode mapping with magnetic resonance imaging for subthalamic nucleus procedures.

BACKGROUND: Magnetic resonance imaging (MRI) and microelectrode recording (MER) are commonly used to guide stereotactic procedures on the subthalamic nucleus (STN). Little is known about the correlation between the position of the STN as seen on MRI and that as determined by MER mapping. We compared these in 10 patients with Parkinson's disease. METHODS: The position of the STN was determined by intraoperative MER findings and stereotactic axial T2 magnetic resonance images with 2-mm slice thickness. Images were reconstructed in a 3-dimensional workstation. The anterior, posterior, medial, lateral, dorsal, and ventral borders of the STN defined with the MRI were measured relative to the midcommissural point. The location of STN activity during MER was reconstructed relative to the midcommissural point for comparison. RESULTS: Twenty-nine tracks recorded with microelectrodes provided clear spans of STN-like activity in 18 STN nuclei. The coordinates of MER were, in general, within the borders of the STN defined with the MRI. However, when analyzed individually, some of the tracks had STN-like activity outside the borders of the MRI-defined nucleus (mostly <1 mm). Three tracks had STN-like activity recorded between 2 and 3 mm more anterior than the anterior border of the nucleus defined with the MRI. CONCLUSIONS: There was a good correlation between MER and the borders of the STN defined in the MRI, except for the anterior-posterior axis, in which MER indicated that the STN extended more anteriorly than as suggested by MRI. This should be taken into account in STN surgery.

Action Potentials↗
PubMed2005

Comparison of three methods of targeting the subthalamic nucleus for chronic stimulation in Parkinson's disease.

OBJECTIVE: The success of subthalamic nucleus (STN) surgery for Parkinson's disease depends on accuracy in target determination. The objective of this study was to determine which of the following techniques was most accurate and precise in identifying the location for stimulation in STN deep brain stimulation surgery that is most clinically effective: direct targeting, indirect targeting using the positions of the anterior and posterior commissures, or a technique using the red nucleus (RN) as an internal fiducial marker. METHODS: We reviewed 14 patients with Parkinson's disease treated with bilateral STN deep brain stimulation (28 STN targets). Electrode implantation was based on direct and indirect targeting using two-dimensional magnetic resonance imaging with refinement using microelectrode recording. Optimal settings, including the contacts used, were determined during the clinical follow-up. The position of the best contact was defined with postoperative magnetic resonance imaging. This location was compared with the modified direct, indirect, and RN-based targets. The mean distances between the targets and the final position of the optimal contact were calculated. The accuracy and variance of each target were analyzed. RESULTS: The mean position of the best contact was x = 12.12 (standard deviation [SD], 1.45 mm), y = -2.41 (SD, 1.63 mm), and z = -2.39 (SD, 1.49 mm) relative to the midcommissural point. The mean distance between the optimal contact position and the planned target was 3.19 mm (SD, 1.19 mm) using the RN-based method, 3.42 mm (SD, 1.34 mm) using indirect targeting, and 4.66 mm (SD, 1.33 mm) using a modified direct target. The mean distance between the optimal contact and the RN-based target was significantly smaller than the mean distance between the optimal contact and the direct target (post hoc with Tamhane's correction, P < 0.001) but not between the optimal contact and the indirect target. The RN-based target had the smallest variance (F test, P < 0.001), indicating greater precision. CONCLUSION: The use of the RN as an internal fiducial marker for targeting the optimal region of STN stimulation was reliable and closely approximates the position of the electrode contact that provides the optimal clinical results.

Deep Brain Stimulation↗
PubMed2005

Bilateral subthalamic nucleus stimulation for Parkinson's disease: a systematic review of the clinical literature.

OBJECTIVE: To evaluate the benefits and adverse effects of bilateral subthalamic nucleus stimulation in the treatment of Parkinson's disease (PD) by systematically reviewing the published literature. METHODS: A search of the PubMed database using the key words subthalamic, nucleus, and stimulation yielded 624 articles published between 1966 and December 2003. Only articles that included original, nonduplicated descriptions of patients with PD treated with bilateral subthalamic nucleus stimulation were selected for further analysis. RESULTS: A total of 38 studies from 34 neurosurgical centers in 13 countries were identified for critical review. The outcomes for 471 patients with PD treated with bilateral subthalamic nucleus stimulation were assessed according to the Unified Parkinson's Disease Rating Scale in both on-medication and off-medication conditions. With stimulation, Unified Parkinson's Disease Rating Scale motor scores in the off-medication condition improved by 50% after 6 months, 56% after 12 months, 51% after 2 years, and 49% after 5 years compared with preoperative off-medication scores. At 12 months of subthalamic nucleus stimulation, the mean improvement in tremor was 81%, in rigidity was 63%, in bradykinesia was 52%, in gait was 64%, and in postural instability was 69% when compared with preoperative off-medication subscores. On-medication dyskinesias were reduced by 94%, as assessed 12 months after stimulation using the Unified Parkinson's Disease Rating Scale IV complications of therapy score. There was an overall 52% reduction in the l-dopa-equivalent dose intake after 12 months of stimulation. Most adverse effects were mild to moderate. There was a 1 to 2% incidence of severe adverse effects (death or permanent neurological deficits related to intracerebral hemorrhages). Nineteen percent of the patients had adverse effects related to stimulation that could be reversed by changing stimulation parameters. There was a 9% incidence of adverse effects related to the hardware (infections, lead and pulse generator problems). CONCLUSION: Bilateral subthalamic nucleus stimulation is effective in the treatment of PD. Further refinements in patient selection and surgical technique may lessen the incidence of complications associated with this procedure.

Electric Stimulation Therapy↗
PubMed2004

Deep brain stimulation in the treatment of dyskinesia and dystonia.

Deep brain stimulation (DBS) has become a mainstay of treatment for patients with movement disorders. This modality is directed at modulating pathological activity within basal ganglia output structures by stimulating some of their nuclei, such as the subthalamic nucleus (STN) and the globus pallidus internus (GPi), without making permanent lesions. With the accumulation of experience, indications for the use of DBS have become clearer and the effectiveness and limitations of this form of therapy in different clinical conditions have been better appreciated. In this review the authors discuss the efficacy of DBS in the treatment of dystonia and levodopa-induced dyskinesias. The use of DBS of the STN and GPi is very effective for the treatment of movement disorders induced by levodopa. The relative benefits of using the GPi as opposed to the STN as a target are still being investigated. Bilateral GPi stimulation is gaining importance in the therapeutic armamentarium for the treatment of dystonia. The DYT1 forms of generalized dystonia and cervical dystonias respond to DBS better than secondary dystonia does. Discrimination between the diverse forms of dystonia and a better understanding of the pathophysiological features of this condition will serve as a platform for improved outcomes.

Dyskinesia, Drug-Induced↗
PubMed2004

Bilateral anterior thalamic nucleus lesions and high-frequency stimulation are protective against pilocarpine-induced seizures and status epilepticus.

OBJECTIVE: The thalamus is thought to play an important role in secondary generalization of seizures. The aim of the present study was to investigate the influence of anterior thalamic nucleus lesions and high-frequency stimulation in the pilocarpine model of secondarily generalized seizures in rats. METHODS: Adult Wistar rats underwent unilateral (n = 7) or bilateral anterior nucleus thalamotomies (n = 10), or unilateral (n = 4) or bilateral (n = 9) anterior thalamic nucleus stimulation through implanted electrodes. Control animals (n = 9) received bilateral implants but no stimulation. Seven days after these procedures, animals were provided pilocarpine (320 mg/kg intraperitoneally) to induce seizures and status epilepticus (SE). Electrographic recordings from hippocampal and cortical electrodes were evaluated, and ictal behavior was assessed. RESULTS: In the control group, 67% of the animals developed SE 15.3 +/- 8.8 minutes after pilocarpine administration. Neither unilateral anterior nucleus lesions nor stimulation significantly reduced the propensity or latency for developing seizures and SE. Bilateral thalamic stimulation did not prevent SE (observed in 56% of the animals), but it significantly prolonged the latency to its development (48.4 +/- 17.7 min, P = 0.02). Strikingly, no animal with bilateral anterior nucleus thalamotomies developed seizures or SE with pilocarpine. CONCLUSION: Bilateral anterior thalamic nuclear complex stimulation and thalamotomies were protective against SE induced by pilocarpine.

Animals↗
PubMed2004

Cingulotomy for psychiatric disease: microelectrode guidance, a callosal reference system for documenting lesion location, and clinical results.

OBJECTIVE: To evaluate magnetic resonance imaging (MRI)- and microelectrode recording-guided cingulotomy for patients with psychiatric disorders and to develop a new method of mapping lesion location in anterior cingulate cortex that takes into account the significant interindividual variability in callosal morphometry. METHODS: MRI and microelectrode recording were used to guide placement of radiofrequency lesions in patients with obsessive-compulsive disorder (n = 21) or affective disorders (n = 5). Postoperative improvement was evaluated with the Yale-Brown Obsessive-Compulsive Scale in 15 of the 21 obsessive-compulsive disorder patients studied. From the postoperative MRI scans, we developed a coordinate system for position in the anterior cingulate cortex. The callosal line passes from the most anterior point of the corpus callosum (c = 0) to the most posterior (c = 100). We reconstructed the lesions onto a sagittal map from the Talairach and Tournoux atlas using the distance along the callosal line and the distance above the upper surface of the corpus callosum. RESULTS: The location of neuronal activity distinguished gray and white matter and was useful in delineating the upper and lower cortical banks of the cingulate gyrus, the cingulate bundle, and the corpus callosum. This information was used to place the lesions. Lesions typically were 6 to 8 mm in diameter on T2-weighted MRI scans. The inferior margins were along the corpus callosum from c = 16 to c = 38. Four of 15 patients with obsessive-compulsive disorder had a documented decrease of more than 35% on the Yale-Brown Obsessive-Compulsive Scale, but only one patient had a sustained benefit for more than 1 year. CONCLUSION: Microelectrode recording is useful for lesion placement. Our system for reporting location in anterior cingulate cortex normalizes for differences in callosal morphometry. These techniques may aid future study.

Adult↗
PubMed2004

Tremor cells in the human thalamus: differences among neurological disorders.

OBJECT: Thalamic neurons firing at frequencies synchronous with tremor are thought to play a critical role in the generation and maintenance of tremor. The authors studied the incidence and locations of neurons with tremor-related activity (TRA) in the thalamus of patients with varied pathological conditions-including Parkinson disease (PD), essential tremor (ET), multiple sclerosis (MS), and cerebellar disorders--to determine whether known differences in the effectiveness of thalamic stereotactic procedures for these tremors could be correlated to differences in the incidence or locations of TRA cells. METHODS: Seventy-five operations were performed in 61 patients during which 686 TRA cells were recorded from 440 microelectrode trajectories in the thalamus. The locations of the TRA cells in relation to electrophysiologically defined thalamic nuclei and the commissural coordinates were compared among patient groups. The authors found that TRA cells are present in patients with each of these disorders and that these cells populate several nuclei in the ventral lateral tier of the thalamus. There were no large differences in the locations of TRA cells among the different diagnostic classes, although there was a difference in the incidence of TRA cells in patients with PD, who had greater than 3.8 times more cells per thalamic trajectory than patients with ET and approximately five times more cells than patients with MS or cerebellar disorders. CONCLUSIONS: There was an increased incidence of TRA in the thalamus of patients with PD. The location of thalamic TRA cells in patients with basal ganglia and other tremor disorders was similar.

Adult↗
PubMed2003

The subthalamic nucleus in the context of movement disorders.

The subthalamic nucleus (STN) has been regarded as an important modulator of basal ganglia output. It receives its major afferents from the cerebral cortex, thalamus, globus pallidus externus and brainstem, and projects mainly to both segments of the globus pallidus, substantia nigra, striatum and brainstem. The STN is essentially composed of projection glutamatergic neurons. Lesions of the STN induce choreiform abnormal movements and ballism on the contralateral side of the body. In animal models of Parkinson's disease this nucleus may be dysfunctional and neurons may fire in oscillatory patterns that can be closely related to tremor. Both STN lesions and high frequency stimulation ameliorate the major motor symptoms of parkinsonism in humans and animal models of Parkinson's disease and reverse certain electrophysiological and metabolic consequences of dopamine depletion. These new findings have led to a renewed interest in the STN. The aim of the present article is to review briefly the major anatomical, pharmacological and physiological aspects of the STN, as well as its involvement in the pathophysiology and treatment of Parkinson's disease.

Animals↗
PubMed2003

Intraventricular pressure monitoring in patients with thalamic and ganglionic hemorrhages.

In the present study, we have evaluated the use of intraventricular pressure catheters in thalamic and ganglionic hemorrhages. Ten patients admitted in our Emergency Department in Glasgow Coma Scale (GCS) equal or below 13 enrolled the study (at least one point should have been lost in the eye opening score to exclude purely aphasic patients that were fully alert). After a complete clinical and neurological evaluation, computed tomography scans were obtained and the volume of the hematomas, as well as presence or absence of hydrocephalus, were considered. Intraventricular pressure catheters connected in parallel to external derivation systems were implanted and patients were thereafter sent to the ICU. Patients that presented mass effect lesions with sustained increased ICP levels or clinical and neurological deterioration were submitted in addition, to the surgical evacuation of the hematomas. Clinical evolution, complications and the rehabilitation of the patients were recorded. Clinical outcome was assessed with the Glasgow Outcome Score. In all but three patients the initial intracranial pressure levels were bellow 20 mmHg (mean for all patients was 14.1 +/- 6.5 mmHg). Notwithstanding, these three patients were extremely difficult to treat. For this group of patients mortality was 100%. Among the patients that presented ICP levels bellow 20 mmHg, 04 developed hydrocephalus and 03 did not display ventricular dilation. As expected, the major benefits concerning the intraventricular pressure catheters connected in parallel with external derivation systems were observed in the group of patients that presented ICP levels bellow 20 mmHg and had hydrocephalus. Mild non-statistically significant correlations for all the three groups were achieved either when the initial GCS and ICP levels (r=-0.28, p=0.43) or when ICP levels and the volumes of the hematomas were compared (r=0.38, p=0.28). In addition, no significant correlations were observed concerning the final outcome of the patients and the variables previously evaluated.

Adult↗
PubMed2003

Physiology and pathophysiology of Parkinson's disease.

The behavior of neurons in the basal ganglia is severely disrupted in Parkinson's disease (PD). In nonhuman parkinsonian primate models, the disturbance in neurons in basal ganglia output structures include increased firing, bursting, an augmented synchrony, correlated activity, and a tendency towards loss of specificity in their receptive fields. This abnormal neuronal behavior, transmitted to the thalamus, cortex and brainstem, is thought to disrupt the functioning of the motor system and underlie the major motor manifestations of PD-tremor, rigidity, akinesia, gait, and postural disturbances. The mainstay of treatment has been to replace the missing dopamine with medication. With time and disease progression, however, dopamine replacement becomes less efficacious and new adverse effects, including the development of motor fluctuations and drug-induced involuntary movements or dyskinesias, emerge. When the patients reach this stage, surgical therapy becomes an option. Most surgical interventions are performed at the level of the thalamus, globus pallidus, and subthalamic nucleus, aiming at the disruption of the pathological activity that accompanies the Parkinson's deficiency state. With this abnormal neuronal activity neutralized, normal movements can in many cases be restored.

Animals↗