Ashwin Viswanathan

Deep Brain Stimulation for Tourette Syndrome: Target Selection

Background/Aims: Tourette syndrome (TS) is a complex neurological disorder manifested chiefly by motor and phonic tics and a variety of behavioral comorbidities, including attention disorder, obsessive-compulsive disorder and impulse control problems. Surgical treatment is increasingly considered when tics become troublesome or even disabling or self-injurious despite optimal medical therapy. In this review, we describe the surgical techniques, stimulation parameters, outcomes of deep brain stimulation (DBS) in TS, and critically review target choices. Methods: A search of the PubMed database was performed to identify all articles discussing DBS and TS. ‘Tourette’ and ‘Stimulation’ were used as MeSH headings. Results: Since the first report of thalamic DBS for TS in 1999, follow-up on less than 100 patients has been reported in the literature. Reported targets for DBS include the thalamic centromedian nucleus and substantia periventricularis, posteroventral globus pallidus internus, ventromedial globus pallidus internus, globus pallidus externus, anterior limb of the internal capsule and nucleus accumbens. Conclusions: Determination of the optimal surgical target will require a multicenter, randomized trial, and an expanded understanding of the neurobiology of TS.

Deep brain stimulation entrains local neuronal firing in human globus pallidus internus

Deep brain stimulation (DBS) in the internal segment of the globus pallidus (GPi) relieves the motor symptoms of Parkinsons disease, yet the mechanism of action remains uncertain. To address the question of how therapeutic stimulation changes neuronal firing in the human brain, we studied the effects of GPi stimulation on local neurons in unanesthetized patients. Eleven patients with idiopathic Parkinsons disease consented to participate in neuronal recordings during stimulator implantation surgery. A recording microelectrode and a DBS macroelectrode were advanced through the GPi in parallel until a single neuron was isolated. After a baseline period, stimulation was initiated with varying voltages and different stimulation sites. The intra-operative stimulation parameters (1-8 V, 88-180 Hz, 0.1-ms pulses) were comparable with the postoperative DBS settings. Stimulation in the GPi did not silence local neuronal activity uniformly, but instead loosely entrained firing and decreased net activity in a voltage-dependent fashion. Most neurons had decreased activity during stimulation, although some increased or did not change firing rate. Thirty-three of 45 neurons displayed complex patterns of entrainment during stimulation, and burst-firing was decreased consistently after stimulation. Recorded spike trains from patients were used as input into a model of a thalamocortical relay neuron. Only spike trains that occurred during therapeutically relevant voltages significantly reduced transmission error, an effect attributable to changes in firing patterns. These data indicate that DBS in the human GPi does not silence neuronal activity, but instead disrupts the pathological firing patterns through loose entrainment of neuronal activity.

The Consequence of Delayed Neurosurgical Care at Tikur Anbessa Hospital, Addis Ababa, Ethiopia

Tikur Anbessa Hospital (TAH) is the major teaching hospital for Addis Ababa University and the only tertiary referral hospital for neurosurgery in Ethiopia. We explore the consequence of delayed treatment by examining the current system in place for treating patients and the wait times experienced by patients. A retrospective chart review was carried out on patients who received a neurosurgical operation at TAH between January 1 and June 30, 2007. We divided patients into those requiring an elective procedure and those requiring emergency surgical care. Based on data entered in the chart, we determined the length of time from symptom onset to neurosurgical consultation and the time from consultation to receiving an operation. Selective cases were chosen to illustrate the effects of delayed care. A total of 172 neurosurgical operations were performed between January 1 and June 30, 2007, at TAH. Of these, 107 (62.2%) charts were available for retrospective review. Fifty-six elective cases were reviewed. The median time from symptom onset to neurosurgical consultation was 185 days. The median time from neurosurgical consultation to operation was 44 days. Fifty-one trauma/emergency surgical cases were reviewed. The median time from symptom onset or traumatic event to neurosurgical consultation was 3 days. The median time from neurosurgical consultation to operation was 1 day. Delayed neurosurgical care comes with a high personal and social cost. By measuring the time from diagnosis to treatment and taking note of institutional practices, changes can be initiated to improve patient waiting times.

Prediction of STN-DBS Electrode Implantation Track in Parkinson's Disease by Using Local Field Potentials.

Optimal electrophysiological placement of the DBS electrode may lead to better long term clinical outcomes. Inter-subject anatomical variability and limitations in stereotaxic neuroimaging increase the complexity of physiological mapping performed in the operating room. Microelectrode single unit neuronal recording remains the most common intraoperative mapping technique, but requires significant expertise and is fraught by potential technical difficulties including robust measurement of the signal. In contrast, local field potentials (LFPs), owing to their oscillatory and robust nature and being more correlated with the disease symptoms, can overcome these technical issues. Therefore, we hypothesized that multiple spectral features extracted from microelectrode-recorded LFPs could be used to automate the identification of the optimal track and the STN localization. In this regard, we recorded LFPs from microelectrodes in three tracks from 22 patients during DBS electrode implantation surgery at different depths and aimed to predict the track selected by the neurosurgeon based on the interpretation of single unit recordings. A least mean square (LMS) algorithm was used to de-correlate LFPs in each track, in order to remove common activity between channels and increase their spatial specificity. Subband power in the beta band (11–32 Hz) and high frequency range (200–450 Hz) were extracted from the de-correlated LFP data and used as features. A linear discriminant analysis (LDA) method was applied both for the localization of the dorsal border of STN and the prediction of the optimal track. By fusing the information from these low and high frequency bands, the dorsal border of STN was localized with a root mean square (RMS) error of 1.22 mm. The prediction accuracy for the optimal track was 80%. Individual beta band (11–32 Hz) and the range of high frequency oscillations (200–450 Hz) provided prediction accuracies of 72 and 68% respectively. The best prediction result obtained with monopolar LFP data was 68%. These results establish the initial evidence that LFPs can be strategically fused with computational intelligence in the operating room for STN localization and the selection of the track for chronic DBS electrode implantation.

GPi Oscillatory Activity Differentiates Tics from the Resting State, Voluntary Movements, and the Unmedicated Parkinsonian State.

Background: Deep brain stimulation (DBS) is an emerging treatment strategy for severe, medication-refractory Tourette syndrome (TS). Thalamic (Cm-Pf) and pallidal (including globus pallidus interna, GPi) targets have been the most investigated. While the neurophysiological correlates of Parkinsons disease (PD) in the GPi and subthalamic nucleus (STN) are increasingly recognized, these patterns are not well characterized in other disease states. Recent findings indicate that the cross-frequency coupling (CFC) between beta band and high frequency oscillations (HFOs) within the STN in PD patients is pathologic. Methods: We recorded intraoperative local field potentials (LFPs) from the postero-ventrolateral GPi in three adult patients with TS at rest, during voluntary movements, and during tic activity and compared them to the intraoperative GPi-LFP activity recorded from four unmedicated PD patients at rest. Results: In all PD patients, we noted excessive beta band activity (13–30 Hz) at rest which consistently modulated the amplitude of the co-existent HFOs observed between 200 and 400 Hz, indicating the presence of beta-HFO CFC. In all 3TS patients at rest, we observed theta band activity (4–7 Hz) and HFOs. Two patients had beta band activity, though at lower power than theta oscillations. Tic activity was associated with increased high frequency (200–400 Hz) and gamma band (35–200 Hz) activity. There was no beta-HFO CFC in TS patients at rest. However, CFC between the phase of 5–10 Hz band activity and the amplitude of HFOs was found in two TS patients. During tics, this shifted to CFC between the phase of beta band activity and the amplitude of HFOs in all subjects. Conclusions: To our knowledge this is the first study that shows that beta-HFO CFC exists in the GPi of TS patients during tics and at rest in PD patients, and suggests that this pattern might be specific to pathologic/involuntary movements. Furthermore, our findings suggest that during tics, resting state 5–10 Hz-HFO CFC shifts to beta-HFO CFC which can be used to trigger stimulation in a closed loop system when tics are present.

Trigeminal and Glossopharyngeal Neuralgia

Trigeminal neuralgia and glossopharyngeal neuralgia are two causes of paroxysmal craniofacial pain. Either can be debilitating in affected individuals. This article reviews the epidemiology, pathogenesis, diagnosis, and treatment options for these disorders.

Radiofrequency lesioning through deep brain stimulation electrodes: A pilot study of lesion geometry and temperature characteristics

Deep brain stimulation (DBS) electrodes have been used effectively to perform radiofrequency lesions in the brain. This study aimed to characterize lesion geometry and peak tissue temperature achieved when lesioning through DBS electrodes. Fresh bovine liver was chosen for a medium as the tissue reliably changes color between 45 and 50 °C. Medtronic 3387 DBS electrodes (Medtronic Sofamor Danek, Inc., Memphis, TN, USA) and the Cosman G4 Radiofrequency Generator (Cosman Medical, Inc., Burlington, MA, USA) were used for lesioning. Bipolar lesions were created at currents between 25 mA and 100 mA for 60-120 seconds. Peak tissue temperature was monitored with Cosman disposable cordotomy electrode (LCED; Cosman Medical Inc.) and recorded. Photographic analysis of the lesions was performed. Tissue impedance ranged between 800-900 Ohms, and tissue temperature was maintained at 20 °C. With lesions at 25 mA for up to 120 seconds, maximal tissue temperature achieved was 36 °C. This correlated with no visible lesions. At 50 mA, maximal tissue temperature exceeded 100 °C, which was associated with tissue charring. Lesions created at 35 mA and 40 mA led to an increase in tissue temperature of 63 °C and 75 °C, respectively. Lesion size was highly reproducible, increasing from 4.5 mm × 7 mm at 35 mA, to 6 mm × 7.5mm at 50 mA. Preliminary analysis suggests that caution should be exerted in using lesion amplitudes exceeding 40 mA (at 800 Ohms), as peak tissue temperatures in vivo could exceed 100 °C. Further in vivo experiments with imaging correlates are needed to further test the safety of this technique.

Cervical artificial disc replacement: Part 2: Clinical experience with the cervical artificial disc

This article is the second of 2 parts. Cervical total disc replacement represents a new frontier in spine surgery. This article reviews current literature with regard to the indications, clinical and radiologic results, adverse outcomes, and complications of cervical artificial disc replacement (C-ADR). Early clinical and radiologic studies of these prostheses have shown promising results. However, the role of these new devices is still developing. Ongoing multicenter prospective randomized controlled trials will aid in our understanding of the indications for C-ADR. Long-term clinical trials will be needed to determine whether cervical arthroplasty fulfills the promise of reduced adjacent segment degeneration and preservation of motion and biomechanical properties of the cervical spine. Surgeon preference among the various C-ADR designs will ultimately be based on clinical outcomes, unique indications, ease of implantation, maintenance of motion, and incidence of complications.

DREZotomy in the treatment of cancer pain: a review.

Background: Cancer-related pain is a common problem that may be intractable by medical and neuromodulatory treatment. The dorsal root entry zone (DREZ) is a hyperactive focus in neuropathic pain syndromes, and DREZotomy has been used in selective cases of neuropathic cancer pain. Objective: The aim of this study was to describe the technique of spinal DREZotomy in the treatment of cancer pain and review the relevant published literature. Methods: A PubMed database search for ‘DREZ’, ‘dorsal root entry zone’ and ‘cancer’, and a search of the references of these manuscripts, was undertaken. Results: 14 papers were identified and reviewed that described a total of 123 patients with cancer pain or radiation-induced pain who have been treated with DREZotomy. Though heterogeneous, these studies reported an overall favorable outcome in carefully selected patients with topographically limited pain syndromes. Conclusion: For patients with well-localized neuropathic cancer pain intractable to medical and first-line surgical management, DREZotomy is a viable treatment option. Further prospective studies are needed to evaluate the outcomes of this procedure.

Percutaneous CT-guided cordotomy for the treatment of pediatric cancer pain.

Percutaneous cordotomy using CT guidance has been shown to be a safe and effective means of reducing pain in adults with cancer in 2 large case series. Its effectiveness in pediatric patients, however, has not been reported. Here, the authors present a case of CT-guided percutaneous cordotomy being used effectively for the treatment of unilateral limb pain in a 9-year-old boy suffering from metastatic medulloblastoma. The efficacy and minimally invasive nature of this procedure support its use in selected pediatric cases.