Primary generalized seizure disorder: correlation of epileptiform discharges with seizure frequency

[Significance of the EEG in the diagnosis of epilepsy]

The electroencephalogram (EEG) is a specific diagnostic method for the evaluation of patients with epilepsies. Interictal epileptiform discharges (IED) recorded in the seizure interval have a high association with the clinical diagnosis of epilepsy. IEDs have to be differentiated from normal variants that resemble IEDs. The EEG may help in the localization of the epileptogenic zone and in the syndrome classification, which is important for therapy and prognosis.

The Progression of Epilepsy

Prognosis for seizure control and cognitive development varies considerably among syndromes. Several factors may interact to influence outcome of an epilepsy including a causative etiology, ictal and interictal discharges, seizure-related trauma or systemic perturbations, and antiepileptic drug (AED) effects. Clinical evidence convincingly supporting Gowers' hypothesis that seizures beget seizures is lacking. Short-term seizure suppression by early treatment does not appear to influence long-term prognosis. Malignant epilepsy syndromes usually begin in infancy or childhood, have a high seizure frequency, resist the initial AED, and are often associated with progressive cognitive dysfunction. Prompt management of some severe epilepsy syndromes may lessen cognitive decline. However, aggressive AEDs therapy must be balanced against the potential for cognitive side effects, particularly if multiple AEDs are used. Several experimental paradigms closely parallel human TLE as both have an initial precipitating injury (IPI), a latent period, then recurrent spontaneous seizures. In humans, an IPI is any medical event with neurological implications. Although transition from a latent period to a seizure disorder certainly constitutes "progression" of the disorder, convincing clinical evidence of subsequent worsening has not emerged. Substantial clinical and experimental evidence indicates some cognitive regression and focal atrophy with time for TLE and other intractable syndromes. However, seizure frequency and severity, established early in the disorder, appear stable in most patients, and even regress in benign syndromes. Factors mitigating or extinguishing epilepsies need to be further sought.

Clinical trials for treatment of primary generalized epilepsies

PURPOSE

To review the current state of knowledge of the treatment of primary (idiopathic) generalized epilepsy syndromes based on the efficacy results of clinical trials, to highlight obstacles in the design of these trials, and to suggest solutions for future research.

METHODS

Published reports of controlled clinical trials, as well as large or significant uncontrolled trials of treatments for these syndromes, were reviewed. Trials were selected for discussion based on their importance or their illustration of design issues.

RESULTS

Only a few randomized, controlled trials of therapy for these syndromes exist. Conclusions based on this Class I data include efficacy in absence epilepsies for ethosuximide, valproate, and lamotrigine, and for eight drugs for primary generalized tonic-clonic seizures. Many commonly accepted therapeutic strategies are not based on formal data. No controlled data exist for uncommon syndromes.

CONCLUSIONS

More clinical trials of therapies for primary generalized epilepsies are needed. To overcome design obstacles, better funding, multicenter cooperation, inclusion of children, study designs requiring fewer patients, equivalent-control designs, use of EEG and video seizure counting, and better syndrome identification will be required.

Invited review: clinical and basic neurophysiology of generalised epilepsies

Electroencephalography (EEG) clarifies several aspects of generalised epileptic seizures and epilepsies. For the clinician, it assists in the diagnosis of the epileptic condition and helps assign the disorder to an appropriate syndrome. This assignation and the quantity of epileptic discharges estimate severity and prognosis. When combined with relevant basic science investigations, EEG studies may disclose significant pathophysiological mechanisms. Therefore, this paper first describes EEG characteristics of the several disorders included under the broad category of "generalised". The review then relates these phenomena to germane experimental data intending that this binocular survey will provide a more meaningful perspective of these disorders.

Valproate monotherapy in juvenile myoclonic epilepsy: dose-related effects on electroencephalographic and other neurophysiologic tests

A neurophysiologic test battery (consisting of a 24-hour, seven-channel electroencephalogram [EEG], EEG spectral analysis, multiple sleep latency test, visual evoked potentials, critical flicker fusion, and visual contrast sensitivity) was administered twice to 16 patients with juvenile myoclonic epilepsy (JME) in a double-blind, randomized, crossover study comparing two daily doses of sodium valproate (VPA), 1000 mg and 2000 mg. Clinical observation time was 6 months for each dose. Mean total VPA concentration during low-dose treatment was 470.4 mmol/L and during high-dose treatment was 700.0 mmol/L. Ten patients had seizures during low-dose treatment, but only three of these showed spike-wave activity on EEGs. During high-dose treatment, nine patients had seizures; five of these had spike-wave activity. EEG power spectrum did not change between doses. The other tests also showed no change between doses. Our results suggested that EEG and our selection of other neurophysiologic tests were of limited value for monitoring seizure frequency and clinical effects of VPA.

Treatment of epilepsy with multiple subpial transections: an acute histologic analysis in human subjects

Multiple subpial transection (MST) is a new surgical technique for treating seizures that arise from functionally critical cortical areas. It has a reported efficacy comparable to that of standard temporal lobe resections. Although the mechanism through which MST works is unknown, the carefully controlled lesions, placed 5 mm apart at the midlevel of the cortical gyri, could produce fiber damage that would prevent horizontal synchronization and spread of epileptic discharges while allowing normal cortical functions such as those related to movement or speech to be preserved. We studied the acute neuropathological features associated with MST in 8 patients with intractable temporal lobe epilepsy. Transections were made along major temporal gyri just before standard lobectomy was performed. After resection, tissue was processed by conventional histological and immunocytochemical techniques. Macroscopically, subpial transections (STs) were perpendicular to the main gyral axis and had an appropriate spacing. Microscopically, most of the lesions were perpendicular and at midlevel. However, many transections involved the lateral aspects of the small gyri, resulting in oblique or deep STs, some of which reached the gray-white matter junction due to the complex microscopic neocortical architecture, in which small gyri are superimposed on major lobar gyri, and to the variable cortical thickness. Extensive acute pyknosis and tissue edema were also evident adjacent to the transections. These changes were variable and extenDed 1-3 mm laterally as irregular columnar blocks. In the deep lesions, myelin pallor and decreased neurofilament immunoreactivity were observed in the white matter. Based on the distribution of STs and their adjacent parenchymal injury, we conclude that this technique produces block-type lesions that probably disrupt propagation of epileptogenic activity. In most instances, midlevel horizontal fibers are damaged; one third of the cases showed additional deep injury that would sever afferent and efferent axons. Therefore, in addition to horizontal desynchronization, a deafferentation mechanism involving different fiber systems may contribute to the anti-seizure effects of MST. We hypothesize that preservation of cortical function is mediated by cortex remaining in the sulcus and gyral crown and possibly by reorganization of tissue adjacent to transections.