Progressive Myoclonic Epilepsies

Drug Treatment of Progressive Myoclonic Epilepsy

The progressive myoclonic epilepsies (PMEs) represent a rare but devastating group of syndromes characterized by epileptic myoclonus, typically action-induced seizures, neurological regression, medically refractory epilepsy, and a variety of other signs and symptoms depending on the specific syndrome. Most of the PMEs begin in children who are developing as expected, with the onset of the disorder heralded by myoclonic and other seizure types. The conditions are considerably heterogenous, but medical intractability to epilepsy, particularly myoclonic seizures, is a core feature. With the increasing use of molecular genetic techniques, mutations and their abnormal protein products are being delineated, providing a basis for disease-based therapy. However, genetic and enzyme replacement or substrate removal are in the nascent stage, and the primary therapy is through antiepileptic drugs. Epilepsy in children with progressive myoclonic seizures is notoriously difficult to treat. The disorder is rare, so few double-blinded, placebo-controlled trials have been conducted in PME, and drugs are chosen based on small open-label trials or extrapolation of data from drug trials of other syndromes with myoclonic seizures. This review discusses the major PME syndromes and their neurogenetic basis, pathophysiological underpinning, electroencephalographic features, and currently available treatments.

The progressive myoclonic epilepsies

Progressive myoclonic epilepsies are a group of disorders characterised by a relentlessly progressive disease course until death; treatment-resistant epilepsy is just a part of the phenotype. This umbrella term encompasses many diverse conditions, ranging from Lafora body disease to Gaucher's disease. These diseases as a group are important because of a generally poor response to antiepileptic medication, an overall poor prognosis and inheritance risks to siblings or offspring (where there is a proven genetic cause). A correct diagnosis also helps patients and their families to accept and understand the nature of their disease, even if incurable. Here, we discuss the phenotypes of these disorders and summarise the relevant specific investigations to identify the underlying cause.

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.

Zonisamide: review of pharmacology, clinical efficacy, tolerability, and safety

BACKGROUND

Zonisamide (ZNS), a sulphonamide derivative, is a new-generation anticonvulsant with multiple potential mechanisms that contribute to its antiepileptic efficacy and may also explain its as yet incompletely assessed utility for non-seizure disorders such as headaches, neuropathic pain, and weight loss.

OBJECTIVE

A review of the pharmacokinetics, pharmacodynamics, evidence for efficacy in different seizure types and non-seizure conditions, adverse effects, and tolerability of ZNS is presented.

METHODS

A review of all manuscripts published in the English literature on ZNS was performed in preparing this manuscript.

RESULTS/CONCLUSIONS

ZNS has a broad label for use in Japan, while the regulatory bodies in the USA and Europe have approved it for use only as an adjunctive therapy for partial seizures in adults. It has favorable pharmacokinetic characteristics, proven efficacy in seizure disorders, and is well tolerated in long-term use.

Anticonvulsant and neuroprotective effects of the novel nootropic agent nefiracetam on kainic acid-induced seizures in rats

Nefiracetam is a novel pyrrolidone-type nootropic agent, and it has been reported to possess a potential for antiepileptic therapy as well as cognition-enhancing effects. We investigated the anticonvulsant and neuroprotective effects of nefiracetam in kainic acid-induced seizures of rats, compared with levetiracetam and standard antiepileptic drugs. Subcutaneous injection of kainic acid (10 mg/kg) induced typical behavioral seizures such as wet dog shakes and limbic seizures and histopathological changes in the hippocampus (degeneration and loss of pyramidal cells in CA1 to CA4 areas). Nefiracetam (25, 50 and 100 mg/kg po) had no effect on the behavioral seizures and dose-dependently inhibited the hippocampal damage. In contrast, levetiracetam, a pyrrolidone-type antiepileptic drug, inhibited neither. Valproic acid and ethosuximide prevented the hippocampal damage without attenuating the behavioral seizures as nefiracetam. Zonisamide and phenytoin did not inhibit the behavioral seizures, while zonisamide enhanced the hippocampal damage and phenytoin increased the lethality rate. Carbamazepine inhibited the behavioral seizures at 50 mg/kg and enhanced that at 100 mg/kg, and it completely inhibited the hippocampal damage at both doses. We have previously reported that anticonvulsant spectrum of nefiracetam paralleled that of zonisamide, phenytoin or carbamazepine in standard screening models. However, the pharmacological profile of nefiracetam was closer to valproic acid or ethosuximide than that of zonisamide, phenytoin or carbamazepine in this study. These results suggest that anticonvulsant spectrum and mechanism of nefiracetam are distinct from those of standard antiepileptic drugs, and nefiracetam possesses a neuroprotective effect that is unrelated to seizure inhibition.

Effects of Nefiracetam, a novel pyrrolidone-type nootropic agent, on the amygdala-kindled seizures in rats

PURPOSE

Nefiracetam (NEF) is a novel pyrrolidonetype nootropic agent, and it has been reported to possess various pharmacologic effects as well as cognition-enhancing effects. The present study focused on the effects of NEF in amygdala-kindled seizures and its potential for antiepileptic therapy.

METHODS

Effects of NEF on fully amygdala-kindled seizures and development of amygdala-kindled seizures were investigated in rats and compared with those of levetiracetam (LEV), a pyrrolidone-type antiepileptic drug (AED).

RESULTS

In fully amygdala-kindled rats, NEF (25, 50, and 100 mg/kg, p.o.) decreased afterdischarge induction, afterdischarge duration, seizure stage, and motor seizure duration in a dose-dependent manner. LEV (25, 50, and 100 mg/kg, p.o.) had no effects on afterdischarge induction and slightly decreased afterdischarge duration, whereas it markedly decreased seizure stage and motor seizure duration. In contrast to the results in fully amygdala-kindled rats, NEF (25 and 50 mg/kg/day, p.o.) had few or no effects on the development of amygdala-kindled seizures. As well as fully amygdala-kindled seizures, LEV (50 mg/kg/day, p.o.) markedly inhibited the development of behavioral seizures without reducing daily afterdischarge duration.

CONCLUSIONS

Although NEF possesses potent anticonvulsant effects on fully amygdala-kindled seizures, it has few or no effects on the development of amygdala-kindled seizures. LEV shows marked anticonvulsant effects on both phases of kindling. In fully amygdala-kindled rats, NEF inhibits both electroencephalographic and behavioral seizures, whereas LEV inhibits only behavioral seizures. This double dissociation suggests that NEF has a distinct anticonvulsant spectrum and mechanisms from those of LEV.

Anticonvulsant properties of the novel nootropic agent nefiracetam in seizure models of mice and rats

PURPOSE

Nefiracetam (NEF) is a novel pyrrolidone-type nootropic agent, and it has been reported to possess various pharmacologic effects as well as cognition-enhancing effects. The present study focused on the anticonvulsant effect of NEF and its potential for antiepileptic therapy.

METHODS

The anticonvulsant properties of NEF were investigated in experimental seizure models of mice and rats, compared with levetiracetam (LEV) and other standard antiepileptic drugs [AEDs; zonisamide (ZNS), phenytoin (PHT), carbamazepine (CBZ), valproic acid (VPA), diazepam (DZP), and ethosuximide (ESM)]. With reference to standard programs for evaluating potential AEDs, the study included the traditional maximal electroshock seizure and subcutaneous chemoconvulsant (pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate) seizure tests and two threshold models (the increasing-current electroshock seizure test and intravenous pentylenetetrazole seizure threshold test). Neurotoxic activities were examined with the rotarod test and traction test.

RESULTS

NEF inhibited electroshock-induced seizures at nontoxic doses, whereas it had no effect on seizures chemically induced by pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate. The anticonvulsant spectrum of NEF paralleled that of ZNS, PHT, and CBZ. The anticonvulsant efficacy of NEF was comparable with that of ZNS and less potent than that of PHT, CBZ, and DZP. However, the safety margin of NEF was superior to that of ZNS, CBZ, VPA, and DZP. LEV showed only slight anticonvulsant effects in threshold models, and it was not effective in conventional screening models.

CONCLUSIONS

These results suggest that NEF has distinct anticonvulsant spectrum and mechanisms from those of LEV. NEF is an orally active and safe AED, and it possesses a potential for antiepileptic therapy.

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.

The Finnish Disease Heritage III: the individual diseases

This article is the third and last in a series entitled The Finnish Disease Heritage I-III. All the 36 rare hereditary diseases belonging to this entity are described for clinical and molecular genetic purposes, based on the Finnish experience gathered over a period of half a century. In addition, five other diseases are mentioned. They may be included in the list of the "Finnish diseases" after adequate complementary studies.