Application of a computational model of vagus nerve stimulation.

OBJECTIVES: The most widely used and studied neurostimulation procedure for medically refractory epilepsy is vagus nerve stimulation (VNS) Therapy. The goal of this study was to develop a computational model for improved understanding of the anatomy and neurophysiology of the vagus nerve as it pertains to the principles of electrical stimulation, aiming to provide clinicians with a systematic and rational understanding of VNS Therapy. MATERIALS AND METHODS: Computational modeling allows the study of electrical stimulation of peripheral nerves. We used finite element electric field models of the vagus nerve with VNS Therapy electrodes to calculate the voltage field for several output currents and studied the effects of two programmable parameters (output current and pulse width) on optimal fiber activation. RESULTS: The mathematical models correlated well with strength-duration curves constructed from actual patient data. In addition, digital constructs of chronic versus acute implant models demonstrated that at a given pulse width and current combination, presence of a 110-µm fibrotic tissue can decrease fiber activation by 50%. Based on our findings, a range of output current settings between 0.75 and 1.75 mA with pulse width settings of 250 or 500 µs may result in optimal stimulation. CONCLUSIONS: The modeling illustrates how to achieve full or nearly full activation of the myelinated fibers of the vagus nerve through output current and pulse width settings. This knowledge will enable clinicians to apply these principles for optimal vagus nerve activation and proceed to adjust duty cycle and frequency to achieve effectiveness.

Risk of adverse events on epilepsy monitoring units: a survey of epilepsy professionals.

In 2008 a workgroup of health care professionals from the American Epilepsy Society (AES) was convened to address the lack of consensus regarding patient care in epilepsy monitoring units (EMUs). The group developed a questionnaire designed to identify the extent to which selected adverse events occurred in EMUs, and it was sent via email to all members of the AES. We asked that only one representative from each center report. Seventy responses were received. The number of centers reporting the following adverse events included: falls by 69%, status epilepticus by 63%, and postictal psychosis by 54%. Infrequent events with serious consequences were also reported including pneumonia by 10%, cardiac arrest by 7%, fractures by 6%, and death by 3% (N=2). Of the 58 respondents who reported using intracranial electrodes, 37.9% (N=22) reported that patients pulled out or dislodged electrodes. This study highlights the need for EMUs to identify and address potential safety risks in their environment, patient population, and system of care.

Adjunctive lamotrigine for partial seizures in patients aged 1 to 24 months.

OBJECTIVE: This randomized, double-blind, placebo-controlled trial was conducted to assess the efficacy and tolerability of adjunctive lamotrigine for the treatment of partial seizures in infants aged 1 to 24 months. METHODS: The study used a responder-enriched design in which all patients received adjunctive lamotrigine during an open-label phase (n = 177; maximum maintenance dose 5.1 mg/kg/day for those on non-enzyme-inducing antiepileptic drugs [AEDs] or valproate and 15.6 mg/kg/day for those on enzyme-inducing AEDs). Patients meeting response criteria were randomly assigned to double-blind treatment for up to 8 weeks with continued lamotrigine (n = 19) or to withdrawal from lamotrigine (placebo; n = 19) while background AEDs were maintained. RESULTS: The proportion of treatment failures (patients who met escape criteria or withdrew before completing the double-blind phase) was lower with lamotrigine (58%) than with placebo (84%). This finding was not significant in the primary analysis (two-sided chi(2) test [primary endpoint]). A post hoc sensitivity analysis of the primary endpoint was also performed (p = 0.045 by one-sided, mid-p corrected Fisher exact test). The median time to meet escape criteria was longer with lamotrigine (42 days) than with placebo (22 days) (p = 0.059). During the last 28 days of the open-label phase, 53% of the patients had a >or=50% reduction in frequency of partial seizures with lamotrigine. Additional reduction in partial seizure frequency was observed during the double-blind phase compared with the last 4 weeks of the open-label phase among those randomly assigned to lamotrigine (32% with a >or=25% reduction) but not those randomly assigned to placebo (5% with a >or=25% reduction). Lamotrigine was well tolerated, with an adverse event profile comparable to that observed in older pediatric patients. CONCLUSION: Lamotrigine was well tolerated, and the data indicate that it may be efficacious in the treatment of partial seizures in infants aged 1 to 24 months.

Practice Parameter: evaluating an apparent unprovoked first seizure in adults (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology and the American Epilepsy Society.

OBJECTIVE: The Quality Standards Subcommittee of the American Academy of Neurology develops practice parameters as strategies for patient care based on analysis of evidence. For this practice parameter the authors reviewed available evidence relevant to evaluating adults presenting with an apparent unprovoked first seizure. METHODS: Relevant questions were defined and addressed by multiple searches of medical literature. Each article was then reviewed, abstracted, and classified using an established evidence scoring system. Conclusions and recommendations were based on a standard three-tiered scheme of evidence classification. RESULTS: For adults presenting with a first seizure, a routine EEG revealed epileptiform abnormalities in approximately 23% of patients, and these were predictive of seizure recurrence. A brain imaging study (CT or MRI) was significantly abnormal in 10% of patients, indicating a possible seizure etiology. Laboratory tests such as blood counts, blood glucose, and electrolyte panels were abnormal in up to 15% of individuals, but abnormalities were minor and did not cause the seizure. Overt clinical signs of infection such as fever typically predicted significant CSF abnormalities on lumbar puncture. Toxicology screening studies were limited, but report some positive tests. RECOMMENDATIONS: EEG should be considered as part of the routine neurodiagnostic evaluation of adults presenting with an apparent unprovoked first seizure (Level B). Brain imaging with CT or MRI should be considered as part of the routine neurodiagnostic evaluation of adults presenting with an apparent unprovoked first seizure (Level B). Laboratory tests, such as blood counts, blood glucose, and electrolyte panels (particularly sodium), lumbar puncture, and toxicology screening may be helpful as determined by the specific clinical circumstances based on the history, physical, and neurologic examination, but there are insufficient data to support or refute recommending any of these tests for the routine evaluation of adults presenting with an apparent first unprovoked seizure (Level U).

Vagus nerve stimulation therapy in pediatric patients with refractory epilepsy: retrospective study.

This six-center, retrospective study evaluated the effectiveness, tolerability, and safety of vagus nerve stimulation in children. Data were available for 125 patients at baseline, 95 patients at 3 months, 56 patients at 6 months, and 12 patients at 12 months. The typical patient, aged 12 years, had onset of seizures at age 2 years and had tried nine anticonvulsants before implantation. Collected data included preimplant history, seizures, implant, device settings, quality of life, and adverse events. Average seizure reduction was 36.1% at 3 months and 44.7% at 6 months. Common adverse events included voice alteration and coughing during stimulation. Rare adverse events, unique to this age group, included increased drooling and increased hyperactivity. Quality of life improved in alertness, verbal communication, school performance, clustering of seizures, and postictal periods. We concluded that vagus nerve stimulation is an effective treatment for medically refractory epilepsy in children.

Vagus nerve stimulation in children with refractory seizures associated with Lennox-Gastaut syndrome.

PURPOSE: Vagus nerve stimulation (VNS) is approved for use for refractory partial seizures. Nevertheless, information regarding VNS therapy for special populations, including Lennox-Gastaut syndrome (LGS) is limited. We discuss the effectiveness, tolerability, and safety of VNS therapy in patients with LGS. METHODS: A six-center, retrospective study evaluated the effectiveness of VNS therapy in patients with LGS at 3 and 6 months and compared preimplant and postimplant seizure frequency. Adverse effects and quality of life (QOL) were included as secondary measures. RESULTS: Fifty patients, median age 13 years, with medically refractory epilepsy, were implanted. Median age at onset of seizures was 1.4 years, and a median of nine anticonvulsants (AEDs) had been tried before implantation. Data-collection forms were designed for retrospectively gathering data on each patient's preimplant history, seizures, implants, device settings, QOL, and adverse events. Median reductions in total seizures were 42% at 1 month, 58.2% at 3 months, and 57.9% at 6 months. The most common adverse events reported were voice alteration and coughing during stimulation. Other uncommon adverse events included increased drooling and behavioral changes. Investigators noted that QOL had improved for some patients in the study. CONCLUSIONS: VNS is an effective treatment for medically refractory epilepsy in LGS. This treatment is well tolerated, safe, and may improve QOL.

Vagal nerve stimulation for status epilepticus.

Refractory generalized convulsive status epilepticus in a 13-year-old boy was halted by left vagal nerve stimulation. Over the next 1.5 years, seizures have continued at a rate and severity which is significantly better than it had been in the year before insertion of the stimulator.

Epilepsy surgery in children with developmental disabilities.

Surgery for treatment of medically uncontrolled epilepsy in children is now widely accepted with reported outcomes similar to those in adults. Epilepsy is reported in 8.8% to 32% of children with mental retardation (MR) and in up to half of children with severe retardation. There has been concern that patients with low IQ will experience unsatisfactory outcomes from epilepsy surgery and not achieve good seizure control. It is appropriate to reassess the prior bias against resective epilepsy surgery in children with MR in view of the changing criteria for potential candidacy for epilepsy surgery in infants and young children. There are three prerequisites for epilepsy surgery: (1) the epilepsy must be medically intractable; (2) the surgery must be feasible, that is, the epileptogenic zone can identified and safely resected; and (3) there is high likelihood of a satisfactory outcome as regards both the epilepsy and the patient's functional status. Patients with MR may have diffuse cerebral dysfunction and diffuse or multifocal epileptogenic regions. Appropriate patient selection is made possible through use of current technology that allows identification of lesions or areas of cerebral dysgenesis, aiding in identification of localized areas of epileptogenesis. Results from various series of patients with MR who have undergone resective surgery for epilepsy have shown that with careful presurgical evaluations, outcomes are similar between patients with normal IQ scores and those with low scores. Surgical protocols specifically for patients with MR and intractable epilepsy are required, including careful definition of desired outcomes.

Topiramate in Lennox-Gastaut syndrome: open-label treatment of patients completing a randomized controlled trial. Topiramate YL Study Group.

PURPOSE: The response to topiramate (TPM) as long-term adjunctive therapy was evaluated in patients with Lennox-Gastaut syndrome (LGS) in a long-term, open-label extension to a double-blind, placebo-controlled trial. METHODS: In 97 patients with LGS (mean age, 11 years), dosages of TPM and concomitant antiepileptic drugs (AEDs) were adjusted to optimal clinical response (mean TPM dosage, 10 mg/kg/day). RESULTS: For those patients who had completed 6 months of TPM therapy, drop attacks were reduced > or =50% in 55% of patients; 15% of patients had no drop attacks for > or =6 months at the last visit. After treatment up to 3+ years, 71% of patients who started open-label TPM were continuing therapy at the last visit. CONCLUSIONS: During long-term therapy, TPM is effective and well tolerated in controlling the treatment-resistant drop attacks and seizures associated with LGS.

Safety and tolerability of topiramate in children.

Three double-blind, randomized, placebo-controlled studies of topiramate that include children have been published and prospective but unblinded and retrospective reviews have been reported providing information regarding topiramate's safety and tolerability. These studies indicate that side effects tend to occur early in treatment with topiramate, especially in children receiving polypharmacy. Two classes of adverse events are commonly reported: central nervous system and anorexia/weight loss. Central nervous system effects include somnolence, difficulties with concentration, and behavior changes. Tolerance to these effects seems to develop in most children. When it occurs, weight loss has been noted in the first 12 to 18 months, after which normal weight gain resumes, without long-term impact on growth. As opposed to the experience in adults, aphasia and word-finding difficulties are not commonly seen, and parasthesiae are not reported by children. Renal calculi are rare. Life-threatening idiosyncratic reactions have not been attributed to topiramate. While metabolic acidosis has been reported, no other clinically significant laboratory abnormalities have been associated with the use of topiramate in children.

Retroperitoneal neuroblastoma widely metastatic to the central nervous system.

A girl with congenital extraadrenal neuroblastoma died at 3 months of age with multiple parenchymal metastases in the brain and spinal cord. The bones of the skull, cranial dura, venous sinuses, and orbits were not involved. Autopsy findings suggest that the tumor penetrated the spinal meninges and disseminated through the cerebrospinal fluid. It is possible that hematogenous metastasis occurred as well. The intracerebral metastases were not identified on a CT scan performed several hours before the child's death.

Cerebrovascular changes in neurofibromatosis.

Vascular changes in neurofibromatosis are most commonly described in the renal arteries. In the present study, two children with neurofibromatosis and cerebral vascular occlusive changes demonstrated by cerebral angiography are reported. Although focal neurological findings in children with neurofibromatosis are often due to tumours, the sudden development of neurological symptoms in such cases should alert paediatricians to the possibility of cerebral vascular disease.

Acute immune complex disease associated with hepatitis. Etiopathogenic and immunopathologic studies of the renal lesion.

Immune deposit glomerulonephritis has been associated with hepatitis B antigenemia. Immune complexes of this antigen and its antibody have been implicated in the pathogenesis of the renal disease. A boy had acute immune complex disease with glomerulitis in which cryoprecipitable complexes of HbsAg and its antibody were isolated from serum. HbsAg was concentrated in the cryoprecipitate and localized in a granular pattern along the glomerular basement membrane in association with immunoglobulins. Glomerular fixed antibody was eluted and shown to be directed against HbsAg. The level of antibody activity to HbsAg was higher in the eluate than the serum, suggesting immunopathogenic specificity of the antibody. The study demonstrates that the nephritis was mediated by immune complexes of HbsAg and its antibody, and the presence of immunoglobulin on the kidney did not represent trapping from the circulation.