Effects of vagus nerve stimulation on progressive myoclonus epilepsy of Unverricht-Lundborg type

Emerging treatments for progressive myoclonus epilepsies

Introduction: Progressive myoclonus epilepsies (PMEs) are a group of neurodegenerative diseases, invariably leading to severe disability or fatal outcome in a few years or decades. Nowadays, PMEs treatment remains challenging with a significant burden of disability for patients. Pharmacotherapy is primarily used to treat seizures, which impact patients' quality of life. However, new approaches have emerged in the last few years, which try to curb the neurological deterioration of PMEs through a better knowledge of the pathogenetic process. This is a review on the newest therapeutic options for the treatment of PMEs.Areas covered: Experimental and clinical results on novel therapeutic approaches for the different forms of PME are reviewed and discussed. Special attention is primarily focused on the efficacy and tolerability outcomes, trying to infer the role novel approaches may have in the future.Expert opinion: The large heterogeneity of disease-causing mechanisms prevents researchers from identifying a single approach to treat PMEs. Understanding of pathophysiologic processes is leading the way to targeted therapies, which, through enzyme replacement or underlying gene defect correction have already proved to potentially strike on neurodegeneration.

The best evidence for progressive myoclonic epilepsy: A pathway to precision therapy

Progressive Myoclonus Epilepsies (PMEs) are a group of uncommon clinically and genetically heterogeneous disorders characterised by myoclonus, generalized epilepsy, and neurological deterioration, including dementia and ataxia. PMEs may have infancy, childhood, juvenile or adult onset, but usually present in late childhood or adolescence, at variance from epileptic encephalopathies, which start with polymorphic seizures in early infancy. Neurophysiologic recordings are suited to describe faithfully the time course of the shock-like muscle contractions which characterize myoclonus. A combination of positive and negative myoclonus is typical of PMEs. The gene defects for most PMEs (Unverricht-Lundborg disease, Lafora disease, several forms of neuronal ceroid lipofuscinoses, myoclonus epilepsy with ragged-red fibers [MERRF], and type 1 and 2 sialidoses) have been identified. PMEs are uncommon disorders, difficult to diagnose in the absence of extensive experience. Thus, aetiology is undetermined in many patients, despite the advance in molecular medicine. Treatment of PMEs remains essentially symptomaticof seizures and myoclonus, together with palliative, supportive, and rehabilitative measures. The response to therapy may initially be relatively favourable, afterwards however, seizures may become more frequent, and progressive neurologic decline occurs. The prognosis of a PME depends on the specific disease. The history of PMEs revealed that the international collaboration and sharing experience is the right way to proceed. This emerging picture and biological insights will allow us to find ways to provide the patients with meaningful treatment.

Total Corpus Callosotomy for Medically Refractory Status Epilepticus Due to Progressive Myoclonic Epilepsy: A Clinically Challenging Case

BACKGROUND

Progressive myoclonic epilepsy (PME) is a syndrome characterized by development of progressive myoclonus, cognitive impairment, and other neurologic deficits. Despite major advances in medical treatment of epilepsy, some PME patients remain refractory to antiepileptic drugs. This may further accentuate cognitive impairment and deteriorate functional capacity. Corpus callosotomy (CC) is used in patients with drug-resistant epilepsy who are not candidates for either excisional epilepsy surgery or neurostimulation. We report the application of the standard complete callosotomy to control medically refractory status epilepticus in a patient with PME.

CASE DESCRIPTION

A 16-year-old boy was referred to the emergency department with generalized tonic-clonic seizures. He was known to have PME since 5 years earlier, with frequent generalized seizures requiring hospitalization and reloading of the drugs. The patient was discussed by the epilepsy surgery working group, and corpus callosotomy was considered as a last resort to control the refractory status epilepticus. The patient experienced no generalized seizures during the 3-month postoperative period (Engel class IIIB).

CONCLUSIONS

Inasmuch as surgery was the last resort to control severe disabling status epilepticus, because most of the epileptogenic discharges were originating from the parieto-occipital regions and profound cognitive impairment was present, we decided to perform a complete rather than just an anterior callosotomy. CC may be considered to prevent secondary generalized seizures as the most disabling attacks in patients with certain epilepsy syndromes. Nevertheless, the impact of palliative surgical intervention on the overall disease course of patients with an underlying diffuse pathologic state remains to be determined.

Rates and Predictors of Seizure Freedom With Vagus Nerve Stimulation for Intractable Epilepsy

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BACKGROUND:

Neuromodulation-based treatments have become increasingly important in epilepsy treatment. Most patients with epilepsy treated with neuromodulation do not achieve complete seizure freedom, and, therefore, previous studies of vagus nerve stimulation (VNS) therapy have focused instead on reduction of seizure frequency as a measure of treatment response.

OBJECTIVE:

To elucidate rates and predictors of seizure freedom with VNS.

METHODS:

We examined 5554 patients from the VNS therapy Patient Outcome Registry, and also performed a systematic review of the literature including 2869 patients across 78 studies.

RESULTS:

Registry data revealed a progressive increase over time in seizure freedom after VNS therapy. Overall, 49% of patients responded to VNS therapy 0 to 4 months after implantation (≥50% reduction seizure frequency), with 5.1% of patients becoming seizure-free, while 63% of patients were responders at 24 to 48 months, with 8.2% achieving seizure freedom. On multivariate analysis, seizure freedom was predicted by age of epilepsy onset >12 years (odds ratio [OR], 1.89; 95% confidence interval [CI], 1.38-2.58), and predominantly generalized seizure type (OR, 1.36; 95% CI, 1.01-1.82), while overall response to VNS was predicted by nonlesional epilepsy (OR, 1.38; 95% CI, 1.06-1.81). Systematic literature review results were consistent with the registry analysis: At 0 to 4 months, 40.0% of patients had responded to VNS, with 2.6% becoming seizure-free, while at last follow-up, 60.1% of individuals were responders, with 8.0% achieving seizure freedom.

CONCLUSION:

Response and seizure freedom rates increase over time with VNS therapy, although complete seizure freedom is achieved in a small percentage of patients.

ABBREVIATIONS:

AED, antiepileptic drug

VNS, vagus nerve stimulation

Time-frequency analysis of intracranial EEG in patients with myoclonic seizures

Myoclonic seizures are defined as generalized seizures according to the classification of seizure by the International League Against Epilepsy (ILAE). The pathogenesis of myoclonic seizures is not yet clear. There are very few studies on the focal surgical treatment of myoclonic seizures. The aim of this study is to investigate the characteristics of myoclonic seizure onset in different bands of the intracranial electroencephalogram (EEG) and their dynamic changes in temporal and spatial evolution. We studied four patients with myoclonic seizures who were under the focal resection of the epileptogenic zone. We retrospectively analyzed the semiology, electrocorticogram (ECoG) and imaging data of these patients, and conducted time-frequency analysis of broadband ECoG activity. We found that myoclonic seizures without clinical lateralizing signs could be improved by the resection of the epileptogenic zone. The ECoG power in different frequency bands increased to a peak at 0.5s before the clinical seizure onset and decreased quickly afterwards. The power of alpha activity was highest during the preictal and ictal periods. The central zone had higher power than the epileptogenic zone in all frequency bands during the preictal period, but this difference was not statistically significant. Our results suggest that myoclonic seizures in some patients might have a focal origination, with a fast bilateral propagating network in all frequency bands, especially the alpha band.

Vagus nerve stimulator in patients with epilepsy: indications and recommendations for use

Epilepsy comprises a set of neurologic and systemic disorders characterized by recurrent spontaneous seizures, and is the most frequent chronic neurologic disorder. In patients with medically refractory epilepsy, therapeutic options are limited to ablative brain surgery, trials of experimental antiepileptic drugs, or palliative surgery. Vagal nerve stimulation is an available palliative procedure of which the mechanism of action is not understood, but with established efficacy for medically refractory epilepsy and low incidence of side-effects. In this paper we discuss the recommendations for VNS use as suggested by the Brazilian League of Epilepsy and the Scientific Department of Epilepsy of the Brazilian Academy of Neurology Committee of Neuromodulation.

Vagus nerve stimulation in Lafora body disease

Introduction

Lafora body disease (LBD) is a rare autosomal recessive disorder characterized by progression to inexorable dementia and frequent occipital seizures, in addition to myoclonus and generalized tonic–clonic seizures (GTCSs). It belongs to the group of progressive myoclonus epilepsies (PMEs), rare inherited neurodegenerative diseases with great clinical and genetic differences, as well as poor prognosis. Since those patients have a pharmacoresistant disease, an adjunctive treatment option is vagus nerve stimulation (VNS). To date, there are four reported cases of the utility of VNS in PME — in Unverricht–Lundborg disease (ULD), myoclonic epilepsy with ragged-red fibers (MERRF), Gaucher's disease, and in one case that remained unclassified.

Case presentation

A 19-year-old male patient had progressive myoclonus, GTCSs that often progressed to status epilepticus (SE), progressive cerebellar and extrapyramidal symptomatology, and dementia, and his disease was pharmacoresistant. We confirmed the diagnosis of LBD by genetic testing. After VNS implantation, in the one-year follow-up period, there was a complete reduction of GTCS and SE, significant regression of myoclonus, and moderate regression of cerebellar symptomatology.

Conclusion

To our knowledge, this is the first reported case of the utility of VNS in LBD. Vagus nerve stimulation therapy may be considered a treatment option for different clinical entities of PME. Further studies with a larger number of patients are needed.

Chronic high-frequency deep-brain stimulation in progressive myoclonic epilepsy in adulthood--report of five cases

PURPOSE

To assess the efficacy and tolerability of chronic high-frequency deep brain stimulation (DBS) in adult patients with progressive myoclonic epilepsy (PME) syndromes.

METHODS

Five adult patients (four male, 28-39 years) with PME underwent chronic high-frequency DBS according to a study protocol that had been approved by the local ethics committee. Electrodes were implanted in the substantia nigra pars reticulata (SNr)/subthalamic nucleus (STN) region in the first patient and additionally in the ventral intermediate nucleus (VIM) bilaterally in the following four cases. Follow-up took place in intervals of 3 months and DBS effects were compared with baseline frequency of passive and activation-induced myoclonic jerks and daily life performance 8 weeks prior to implantation.

KEY FINDINGS

Follow-up periods ranged from 12-42 months (median 24 months). The best clinical effects were seen with SNr/STN DBS in all patients. VIM stimulation failed to achieve acute therapeutic effects and revealed low side-effect thresholds and even triggering of myoclonia. In all patients the reduction of myoclonic seizures was observed and ranged between 30% and 100% as quantified by a standardized video protocol. All patients reported clinically relevant improvements of various capabilities such as free standing and walking or improved fine motor skills. In one patient with an excellent initial response generalized tonic-clonic seizures increased after 3 months of stimulation following extensive trauma-related surgery. The best effect was seen in the least impaired patient.

SIGNIFICANCE

DBS of the SNr/STN may be an effective treatment option for patients with PME. Less impaired patients may benefit more markedly.

Vagal nerve stimulation for drug-resistant epilepsies in different age, aetiology and duration

PURPOSE

The aim of the study was to compare the outcome with respect to age of implant, aetiology and duration of epilepsy.

METHODS

One hundred thirty-five drug-resistant epileptic patients, excluded from ablative surgery, were submitted to vagal nerve stimulation (1995-2007). Aetiology was cryptogenic in 57 and symptomatic in 78 patients. Ages of implant were 0.5-6 years (18 patients), 7-12 years (32 patients), 13-18 years (31 patients) and more than 18 years (54 patients). Epilepsy types were Lennox-Gastaut (18 patients), severe multifocal epilepsy (33 patients) and partial (84 patients). Duration of epilepsy is 3 months to 57 years. Clinical outcome was determined by comparing the seizure frequency after stimulation at 3-6-12-18-24-36 months with the previous 3 months. 'Responders' were the patients experiencing a seizure frequency reduction of 50% or more during follow-up. In statistical analysis, Wilcoxon and McNemar tests, general linear model for repeated measures, logistic regression and survival analysis were used.

RESULTS

The seizure frequency reduction was significant in the group as a whole between baseline and the first follow-up (Wilcoxon test). The percentage of responder increases with time (McNemar test p = 0.04). Univariate analysis showed a significant effect of the age of implant on seizure frequency reduction: Adult patient had worst clinical outcome than children (p < 0.001) and adolescents (p = 0.08). Patients with severe multifocal epilepsy had better percentage seizure reduction compared with Lennox-Gastaut and partial (p = 0.03). Lesser duration of epilepsy had positive influence on outcome. Multivariate analysis confirmed age of implant to be the strongest factor influencing prognosis. Furthermore, positive is the association between lesional aetiology and young age.

CONCLUSIONS

The best responder could be a young lesional epileptic patient; after 3 years of follow-up, the percentage of responders is still in progress.

The efficacy of vagus nerve stimulation in intractable epilepsy associated with nonketotic hyperglycinemia in two children

Nonketotic hyperglycinemia is an inborn error of glycine metabolism and these patients frequently suffer from intractable epilepsy despite treatment with sodium benzoate, dextromethophan, and multiple anticonvulsants. We encountered 2 infants with nonketotic hyperglycinemia whose intractable generalized convulsive seizures were difficult to control with sodium benzoate, dextromethophan, and multiple anticonvulsants. However, after the addition of vagus nerve stimulation, their intractable generalized seizures were >75% reduced in frequency, the numbers of multiple anticonvulsants were reduced, and the quality of life significantly improved. The efficacy in seizure reduction persists for at least 3 years in both children.

Efficacy of vagus nerve stimulation in the treatment of depression

Major depressive disorder is a disease with prominent individual, medical and economic impacts. A relevant proportion of depressive patients suffering from a therapy-resistant course are increasingly being treated with antidepressant brain stimulation techniques. One of these interventions is the vagus nerve stimulation that has recently been tested in a number of clinical trials. To date, the acute and long-term efficacy of vagus nerve stimulation are still under debate. Thus further studies are required, especially since the exact mode of action of vagus nerve stimulation is still not well understood. In this paper we will review the results of existing clinical trials as well as the neurobiological effects measured with neuroimaging, biochemical and electrophysiology approaches.

Treatment options for epileptic myoclonus and epilepsy syndromes associated with myoclonus

BACKGROUND

Myoclonus is a brief shock-like movement that has many different etiologies. The degree to which it disturbs quality of life is extremely variable, as is its response to treatment.

OBJECTIVE

In this review, we focus on the treatment strategies for epileptic myoclonus in some common disorders, and in others that are not so common but where myoclonus is a prominent feature and has been studied more.

METHODS

An extended literature review in the English language was conducted through PubMed and text books.

CONCLUSION

Epileptic myoclonus is a manifestation of cortical irritability. The precise etiology is important when determining the best course of treatment. Response to treatment is variable and usually depends on the epileptic syndrome. Some antiepileptic drugs may worsen myoclonus even in patients with syndromes where most patients have a good response to that same drug. Therefore, clinicians must always have in mind that worsening in myoclonus may be ameliorated by decrease or withdrawal rather than increase of medication.

Vagal nerve stimulation--a 15-year survey of an established treatment modality in epilepsy surgery

Neurostimulation is an emerging treatment for neurological diseases. Electrical stimulation of the tenth cranial nerve or vagus nerve stimulation (VNS) has become a valuable option in the therapeutic armamentarium for patients with refractory epilepsy. It is indicated in patients with refractory epilepsy who are unsuitable candidates for epilepsy surgery or who have had insufficient benefit from such a treatment. Vagus nerve stimulation reduces seizure frequency with > 50% in 1/3 of patients and has a mild side effects profile. Research to elucidate the mechanism of action of vagus nerve stimulation has shown that effective stimulation in humans is primarily mediated by afferent vagal A- and B-fibers. Crucial brainstem and intracranial structures include the locus coeruleus, the nucleus of the solitary tract, the thalamus and limbic structures. Neurotransmitters playing a role may involve the major inhibitory neurotransmitter GABA but also serotoninergic and adrenergic systems. This manuscript reviews the clinical studies investigating efficacy and side effects in patients and the experimental studies aiming to elucidate the mechanims of action.

Clinical picture of EPM1-Unverricht-Lundborg disease

Unverricht-Lundborg disease (ULD), progressive myoclonic epilepsy type 1 (EPM1, OMIM254800), is an autosomal recessively inherited neurodegenerative disorder characterized by age of onset from 6 to 16 years, stimulus-sensitive myoclonus, and tonic-clonic epileptic seizures. Some years after the onset ataxia, incoordination, intentional tremor, and dysarthria develop. Individuals with EPM1 are mentally alert but show emotional lability, depression, and mild decline in intellectual performance over time. The diagnosis of EPM1 can be confirmed by identifying disease-causing mutations in a cysteine protease inhibitor cystatin B (CSTB) gene. Symptomatic pharmacologic and rehabilitative management, including psychosocial support, are the mainstay of EPM1 patients' care. Valproic acid, the first drug of choice, diminishes myoclonus and the frequency of generalized seizures. Clonazepam and high-dose piracetam are used to treat myoclonus, whereas levetiracetam seems to be effective for both myoclonus and generalized seizures. There are a number of agents that aggravate clinical course of EPM1 such as phenytoin aggravating the associated neurologic symptoms or even accelerating cerebellar degeneration. Sodium channel blockers (carbamazepine, oxcarbazepine) and GABAergic drugs (tiagabine, vigabatrin) as well as gabapentin and pregabalin may aggravate myoclonus and myoclonic seizures. EPM1 patients need lifelong clinical follow-up, including evaluation of the drug-treatment and comprehensive rehabilitation.

La maladie d’Unverricht-Lundborg (EPM1)

Unverricht-Lundborg disease (ULD) is the purest and least severe type of progressive myoclonus epilepsy (PME), and is not associated with progressive cognitive deficit. Symptoms stabilize in adulthood, with a varying degree of permanent, often severe handicap that is mostly due to myoclonus. The disorder follows an autosomal recessive transmission pattern, with onset between 8 and 15 years years of age of generalized tonic-clonic or clonic-tonic-clonic seizures, action myoclonus (massive or segmental), photosensitivity, and often ataxia. Prevalence varies, it is highest in certain isolates (Finland, La Réunion Island) and in region with higher levels of inbreeding (Maghreb). ULD is due to a deficit in cystatin B (stefin B), but the mechanisms leading to the clinical symptoms are not well understood. The causative gene, PME1, was identified in 1991 and localized to chromosome 21q22.3. The mutations are mainly expansions of the CCCCGCCCCGCG dodecamer, but less common point mutations were also found. A variant has been recently reported in a Palestinian family, with localization on chromosome 12. The diagnosis of ULD is made on the basis of family history, age at onset, geographical and ethnic context, and on the typical features of myoclonus and epilepsy, in the absence of cognitive and sensory deficits. Neurophysiological evaluation yields interesting, but unspecific results. There are no biological or pathological markers for ULD. Molecular analysis confirms the diagnosis in most patients. Genetic testing for heterozygotes and even prenatal diagnosis are possible, although seldom performed, if the mutation has been identified. In spite of intensive research, ULD has yet to reveal all of its secrets. It remains a quasi "idiopathic" type of PME, with limited progression. Clinicians and patients are still waiting for an etiologically oriented treatment, which should, ideally, be admnistered early in the course of the disease, if possible before the onset of invalidating symptoms.

Progressive myoclonic epilepsies: a review of genetic and therapeutic aspects

The progressive myoclonic epilepsies (PMEs) are a group of symptomatic generalised epilepsies caused by rare disorders, most of which have a genetic component, a debilitating course, and a poor outcome. Challenges with PME arise from difficulty with diagnosis, especially in the early stages of the illness, and further problems of management and drug treatment. Recent advances in molecular genetics have helped achieve better understanding of the different disorders that cause PME. We review the PMEs with emphasis on updated genetics, diagnosis, and therapeutic options.

Nonpharmacologic Treatment of the Catastrophic Epilepsies of Childhood

The catastrophic epilepsy syndromes of childhood are initially treated with a pharmacologic intervention in most cases. However, due to the poor response patients often have to pharmacologic interventions, nonpharmacologic treatment options are an important part of a comprehensive treatment plan for this group of children. Additionally, nonpharmacologic therapy may offer a method to minimize associated morbidity and mortality. This article discusses the use of epilepsy surgery, the ketogenic diet, and vagus nerve stimulation in the treatment of patients with infantile spasms, Lennox-Gastaut syndrome, and progressive myoclonic epilepsy. Efficacy of the nonpharmacologic treatment options, as measured by reduction in seizure frequency, as well as by developmental progress or behavioral improvement, varies according to the specific catastrophic epilepsy disorder and the treatment option.

A review of functional neuroimaging studies of vagus nerve stimulation (VNS)

Vagus nerve stimulation (VNS) is a new method for preventing and treating seizures, and shows promise as a potential new antidepressant. The mechanisms of action of VNS are still unknown, although the afferent direct and secondary connections of the vagus nerve are well established and are the most likely route of VNS brain effects. Over the past several years, many groups have used functional brain imaging to better understand VNS effects on the brain. Since these studies differ somewhat in their methodologies, findings and conclusions, at first glance, this literature may appear inconsistent. Although disagreement exists regarding the specific locations and the direction of brain activation, the differences across studies are largely due to different methods, and the results are not entirely inconsistent. We provide an overview of these functional imaging studies of VNS. PET (positron emission tomography) and SPECT (single photon emission computed tomography) studies have implicated several brain areas affected by VNS, without being able to define the key structures consistently and immediately activated by VNS. BOLD (blood oxygen level dependent) fMRI (functional magnetic resonance imaging), with its relatively high spatio-temporal resolution, performed during VNS, can reveal the location and level of the brain's immediate response to VNS. As a whole, these studies demonstrate that VNS causes immediate and longer-term changes in brain regions with vagus innervations and which have been implicated in neuropsychiatric disorders. These include the thalamus, cerebellum, orbitofrontal cortex, limbic system, hypothalamus, and medulla. Functional neuroimaging studies have the potential to provide greater insight into the brain circuitry behind the activity of VNS.

Treatment Strategies for Myoclonic Seizures and Epilepsy Syndromes with Myoclonic Seizures

Despite the availability of numerous treatment options, the diagnosis and treatment of myoclonic seizures continue to be challenging. Based on clinical experience, valproate and benzodiazepines have historically been used to treat myoclonic seizures. However, many more treatment options exist today, and the clinician must match the appropriate treatment with the patient's epilepsy syndrome and its underlying etiology. Comorbidities and other medications must also be considered when making decisions regarding treatment. Rarely, some antiepileptic drugs may exacerbate myoclonic seizures. Most epileptic myoclonus can be treated pharmacologically, but some cases respond better to surgery, the ketogenic diet, or vagus nerve stimulation. Because myoclonic seizures can be difficult to treat, clinicians should be flexible in their approach and tailor therapy to each patient.

Vagus-nerve stimulation for the treatment of epilepsy

Vagus-nerve stimulation (VNS) is now an accepted treatment for patients with refractory epilepsy. There have been many studies suggesting that VNS affects the brain in such areas as the thalamus and other limbic structures. In addition, there is some evidence that norepinephrine is important in the prophylactic antiseizure effects of VNS. The efficacy of VNS has been established for partial seizure types, even in refractory patients who did not respond to surgical treatment for epilepsy. There are also data, from open-label studies, that suggest efficacy in other seizure types. Therefore, VNS seems to be a broad-spectrum treatment for epilepsy. Improvement is not immediate but increases over 18-24 months of treatment. Most studies report subjective improvements in various quality-of-life measurements during treatment with VNS--objective trials have confirmed this observation. Side-effects are mainly stimulation related and reversible and they tend to decrease over time. They are generally mild to moderate and seldom necessitate the removal of the device. No idiosyncratic side-effects have been reported in 12 years of experience, and VNS does not interact with antiepileptic drugs. Most adverse events are predictable and related to the specific stimulation regimen. VNS does not have cognitive and systemic side-effects and can, therefore, be a valuable treatment approach even for patients who have poor tolerance of antiepileptic drugs.

Treatment considerations: role of vagus nerve stimulator

Epilepsy is considerably more common in individuals with mental retardation and developmental delays than in the general population. Compared with other groups with epilepsy, these individuals have higher seizure burdens, more often experience multiple seizure types, and more frequently have seizures that are medically refractory. The majority of these patients with refractory epilepsy will not have a surgically amenable epilepsy syndrome. For these individuals, the vagus nerve stimulator offers the potential for improved seizure control, abortive treatment of seizures, and medication reduction, which may lead to greater independence and other improvements in quality of life.

Progressive myoclonic epilepsies

The progressive myoclonic epilepsies are a rare but extremely debilitating group of disorders that are difficult to diagnose and even harder to treat. They represent a heterogeneous subgroup of those with secondary generalized epilepsy. Efficacy of treatment is often measured in terms of slowing a patient's inevitable decline. Reviewed here are the classification of progressive myoclonic epilepsies, features of myoclonic seizures, the five most prevalent progressive myoclonic epilepsy syndromes-Unverricht-Lundborg disease, myoclonus epilepsy with ragged red fibers (MERRF) mitochondrial disease, Lafora's disease, neuronal ceroid lipofuscinoses, and sialidoses-and current treatment options.

Vagus nerve stimulation for refractory epilepsy

Vagus nerve stimulation (VNS) is a neurophysiological treatment for patients with medically or surgically refractory epilepsy. Since the first human implant in 1989, more than 10 000 patients have been treated with VNS. Two randomized controlled studies have shown a statistically significant decrease in seizure frequency during a 12-week treatment period versus a baseline period when 'high stimulation' mode was compared with 'low stimulation' mode. The efficacy appears to increase over time. In general, one third of the patients show a >50% reduction of seizure frequency; one third show a 30-50% seizure reduction, and one third of patients show no response. Few patients become seizure-free. Side effects during stimulation are mainly voice alteration, coughing, throat paraesthesia and discomfort. When studied on a long-term basis, VNS is an efficacious, safe and cost-effective treatment not only in adults but also in children and the elderly. The precise mechanism of action remains to be elucidated. In recent years much progress has been made through neurophysiological, neuroanatomical, neurochemical and cerebral blood flow studies in animals and patients treated with VNS. Further elucidation of the mechanism of action of VNS may increase its clinical efficacy and our general understanding of some physiopathological aspects of epilepsy. Finally, VNS may become an alternative treatment for other conditions such as depression and pain.