INTRODUCTION AND HISTORICAL BACKGROUND

Early discussions on the classification of epilepsy have had a marked and lasting impact upon our current understanding of the disease, and might be defined in three major eras: the philosophical era before the 20th century that included patient observation and to a large degree philosophical speculation regarding the nature of the disease; the era of the localizationalists and pathologists, which occurred in the first half of the 20th century; and the molecular era, including neurochemistry and, in particular, receptor pharmacology, the physiology of excitatory and inhibitory systems, and molecular biology.

The Philosophical Era

In 1861, Reynolds (1) described convulsions in children by the name eclampsia. So-called eclamptic seizures in those days referred to seizures characteristic of the childhood age group that encompassed febrile convulsions, and convulsions that formed the basis of specific systemic diseases. Although Poupart had described absence seizure in a young girl in 1705 (2), different seizure types were not particularly related to different age groups until much later. In 1772, Tissot (3) classified epileptic seizures but made a more specific contribution, which is often lost, that was further elaborated by Sachs (4) in the first English-language pediatric neurology textbook. This was the concept that epilepsy is composed of an ongoing predisposing condition or diathesis, and that the individual epileptic seizures, or expressions of the epileptic process, are triggered by a concatenation of factors that might be considered as precipitating or triggering factors. The latter are not always recognized, and epilepsy therefore has been defined as a liability of unprovoked seizures, which is probably a procrustean attempt to exclude febrile convulsions from the epilepsy rubric.

Sachs divided childhood epilepsies into the eclamptic and the epileptic. The epileptic seizures were further divided into focal and generalized as well as lesional and idiopathic. He believed that idiopathic seizures on a heritable basis ultimately had a bad prognosis and that symptomatic seizures had an even worse prognosis. He thought that symptomatic epilepsies were the result of neonatal abnormalities, including brain hemorrhage. Freud (5) wrote about epilepsy in his text on the infantile cerebral palsies and related childhood seizures to major brain disturbances, leading to the conditions being included under the heading of cerebral palsy. Smith (6), in his book on diseases in children published more than 100 years ago, stated that eclampsia in children was relatively benign except when severe and protracted, when it might be the cause of certain lesions. He further separated this from epilepsy occurring in older children, which he regarded as symptomatic. Sachs, agreeing with Tissot in defining an underlying predisposition and a precipitating cause, also stated that the prognosis largely depended on the underlying cause of the epilepsy and was otherwise not inherent in the convulsions, a somewhat different conclusion than had been arrived at by Gowers (7), who predominantly studied adults and who believed that the periodicity or repetitiveness of a convulsive disorder carried within it the seeds of a progressive disorder.

The Localizationalist and Pathologist Era

The period of the localizationalists and pathologists began with the experiments of Fritsch and Hitzig and of Ferrier and formed the basis of Hughlings Jackson’s localizational endeavors. This, in turn, inspired the beginning of epilepsy surgery 100 years ago by Victor Horsley. The landmark activities of Penfield, Erickson, and Jasper during the past 50 years more clearly defined the nature of epileptic seizures and their localization in the nervous system. The development of electroencephalography and video-electroencephalography has contributed to better understanding of epilepsy. This allowed the elaboration of the 1981 classification of epileptic seizures (8), which represented an advance made possible by objective methods of documenting seizures. The addition of other factors, such as anatomic substrate, cause, and age, based on information other than intensive monitoring, were then incorporated into the definitions of individual epileptic syndromes (9).

The Molecular and Genetic Era

The study of the epilepsies has been advanced immensely by modeling of the epilepsies using various animal models; sophisticated neurophysiological, neurochemical, and pharmacological techniques; tissue slice preparations with the application of excitatory and inhibitory neurotransmitters and both extracellular and intracellular recordings; and individual neuronal culture preparations. More recent advances in basic science research, oddly enough, can be seen as taking us back hundreds of years to the original postulates of Tissot regarding epileptogenesis. He postulated that certain factors influenced the threshold for seizures, and others provided acute provocation. Baraban (10) elegantly summarized the parallels in modern scientific studies: Genomic research has identified factors that alter the threshold for seizures, and other factors, including glial activation, may act as acute provocation. With these studies has come the realization of epilepsy as a systemic disease with an interplay of factors alluded to by students of epilepsy hundreds of years ago, the details of which are only becoming clear in the current era.

Historical Summary

This brief history of classification illustrates how many of our current thoughts on epilepsy have been framed by discussions of our predecessors, sometimes dating back to concepts that were developed more than a century ago. Key concepts were the distinction of acute symptomatic seizures from epilepsy, the differentiation of focal and generalized seizures, and the identification of hereditary and structural causative factors. While we acknowledge these contributions, our challenge is to find a way to incorporate new data into classification schemes, based largely upon scientific merit, but also practical purposes.

Evolution of the Classification Schemes

The current schemes still endorsed by the International League Against Epilepsy (ILAE) are the 1981 ILAE classification of seizures and the 1989 ILAE classification of epilepsy syndromes (8,9). These classifications, intimately familiar to all epileptologists and many neurologists, have stood the test of time—a remarkable feat given the fact that these classifications were devised at a time when video-EEG units were just starting to proliferate. Still, some of the terms are clearly outdated (eg, “partial” is out of vogue and has been replaced by “focal,” new syndromes have been recognized in the interim, and some older syndromes have not held up under further scrutiny). Modern genetics is challenging some of our assumptions, like the dialectic of idiopathic versus symptomatic. Some epilepsies with strong genetic prederminants, such as Dravet syndrome, do not phenotypically match other idiopathic (sui generis) epilepsies. Clinical neurophysiological techniques and imaging have shown that seizures previously thought to have been “generalized” are really regional, or even triggered by focal processes. Many have recognized the need, therefore, to change the classification, but the critical question is how. What are the needs of the classification systems? Should they be practical, like a gardener’s system, or scientific, like a botanist’s (11)? If a scientific system is desired—one that provides insight into the underlying shared mechanisms—how is this to be done when we have only an incomplete knowledge of the pathogenesis of most epilepsies (12,13)? In this chapter we also examine the issue of classification from the perspective of an electroencephalographer.

Seizure Classification

Seizures have historically been categorized as either focal or generalized (Table 14.1). Focal (or localization-related) seizures arise in specific loci in the cortex, which carry with them identifiable signatures, either subjective or observational. These may range from disorders of sensation or thought to convulsive movement of a part of the body. Originally, simple focal (partial) seizures were defined as those in which consciousness is preserved. The concept was that these arose from the six-layered isocortex and remained localized sufficiently long to allow specific symptoms to be discerned. In contrast, complex partial (focal) seizures were defined as those in which consciousness was impaired. The implication of complex partial (focal) seizures was that they involved elaboration of the elements of the limbic system, thus leading to early bilateral dysfunction.

TABLE 14.1

Generalized seizures involve large areas of the brain from the outset and are usually bilateral in their initial manifestations and associated with early impairment of consciousness. They may range from absence seizures characterized only by impaired consciousness to generalized tonic–clonic seizures (GTCS) in which widespread convulsive activity takes place. Myoclonic seizures, tonic seizures, and clonic seizures may also occur as generalized attacks.

A more recent proposal from the ILAE for the classification of seizures is shown in Table 14.2 (14). In this revision, the term “focal” replaces the previous term “partial,” and the obligatory separation of partial seizures into simple, complex, and secondary generalized was discarded.

It has been suggested that some information about consciousness be included in the description of the focal seizures (15). The 2010 proposal suggested that the phrase “impairment of consciousness or awareness” was more precise than “complex,” but also made mention of the term “dyscognitive,” which had been previously proposed (16). Others have suggested the simple term “aware” (15).

Semiological Classification Schemes

Lüders and colleagues have a classification system for seizures that has been used in many major epilepsy centers in a wide variety of countries (17). Others have proposed a simplified semiological classification system for use in the very young (18). While seizures may sometimes be broadly classified using the most prominent and early feature of the seizure, the various combinations of features, patterns, and time course of the seizure cannot be adequately summarized in a single word or phrase. Nothing can replace a thorough and meticulous description of the seizure. Indeed, the historic narrative of the seizure, as described or observed by parents, is the single most helpful piece of information allowing proper diagnosis of the seizure disorder, and should be recorded, as accurately as possible, with few or no editorial comments. A simple list of focal and generalized seizures can be constructed based upon semiology (Figure 14.1).

TABLE 14.2

Although the early manifestations of seizures help to define the region of ictal onset, not all early clinical features have equal localizing value. Tassinari and colleagues make the point that some of the automatic motor movements may originate from deep structures that are preprogrammed motor movements, remarkably conserved across species (19). Indeed, clinical features alone cannot always allow one to diagnose a focal seizure correctly. Rather, “focal seizure” is actually an electroclinical diagnosis. It is usually made following consideration of multiple factors related to the patient and the clinical event, but may require EEG confirmation, particularly in the very young (20).

CLASSIFICATION OF EPILEPSIES AND EPILEPTIC SYNDROMES

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