Classification of Epileptic Seizures and Epilepsies

The need for a comprehensive classification of epileptic phenomena has been increasingly recognized. According to Masland (1974), “the development of a uniform and generally accepted classification of disease is an essential step in the understanding of the underlying processes and in establishing communication through which the results of scientific investigation may be compared and evaluated.” Classification of epileptic phenomena is also of practical importance, as medication should be prescribed according to seizure type and syndrome. However, no single code can cover the multiple aspects (e.g., clinical, electroencephalographic [EEG], etiologic, and anatomic) of the various epilepsies (Aicardi, 1986a), and the limited knowledge of the medical community regarding their basic mechanisms does not permit classification based on the physiopathology of the disorder.

Empiric classifications of epilepsies are possible only if they are limited to one aspect of the condition. For example, one might construct classifications based on the etiology of epilepsy (symptomatic versus idiopathic or genetic), the topographic origin of the seizures and the location of the responsible lesion (e.g., insular or occipital epilepsy), or the presumed mechanisms (e.g., corticoreticular or “centrencephalic” epilepsy) (Gloor et al., 1990; Gloor, 1979). Such classifications, however, are not mutually exclusive. Any classification used is inherently imperfect, reflecting primarily the need of its user. For instance, a neurosurgeon working with epilepsy requires a topographic classification, whereas pediatricians or neurologists prefer a system based on the clinical presentation of the attacks or on their course and outcome.

The empiric classification of epileptic seizure types has proven more accessible because it avoids the insuperable difficulties that are associated with the attempts to classify the multiple chronic disorders that are characterized by the recurrent seizures that comprise the epilepsies. An ad hoc committee of the International League Against Epilepsy (ILAE) accepted a first classification of epileptic seizures in 1969 (Gastaut, 1969a).

INTERNATIONAL LEAGUE AGAINST EPILEPSY SEIZURE CLASSIFICATIONS

The 1969 Classification

The 1969 ILAE seizure classification scheme was based on the following six criteria: clinical seizure type, EEG seizure type, EEG interictal expression, anatomic substrate, etiology, and age (Table 2.1). The four main groups that it included were partial seizures, generalized seizures, unilateral or predominantly unilateral seizures, and unclassified epileptic seizures. Partial seizures were defined as those in which the first clinical symptoms indicated the activation of an anatomic and/or functional system of neurons that was limited to a part of a single hemisphere with a correspondingly localized EEG discharge. Partial seizures were further subdivided into the following two subgroups: those with elementary (simple partial seizures) symptomatology and those with complex (complex partial seizures) symptomatology. The term simple or elementary referred to those seizures involving disturbances of the primary motor, sensory, or similar cortical areas. The term complex referred to those seizures involving higher level functions in the widest sense and arising in the so-called association or interpretative cortex, which subserves more elaborate functions than those supported by the primary areas. Generalized seizures were defined as those in which the first clinical changes indicated an initial involvement of both hemispheres. They included several subgroups involving either convulsive or nonconvulsive manifestations.

The 1981 Classification

The 1969 ILAE classification was revised in 1981 (Commission on Classification and Terminology of the International League Against Epilepsy, 1981). The 1981 revision (Table 2.2) classified seizures on the basis of only two criteria: the clinical features and the EEG features of the seizures. In this scheme, partial seizures were subdivided into simple and complex seizures, a division that depended exclusively on the
state of consciousness during the attacks. Simple partial seizures are those during which “consciousness is preserved,” while complex partial seizures are those during which consciousness is absent or disturbed.

TABLE 2.1. International League Against Epilepsy (1969) classification of epileptic seizures

Partial seizures (or seizures beginning locally)
	Partial seizures with elementary symptomatology (generally without impairment of consciousness)
		With motor symptoms: focal motor, jacksonian, versive, postural, somatic inhibitory (?), aphasic, phonatory
		With special sensory or somatosensory symptoms: somatosensory, visual, auditory, olfactory, gustatory, vertiginous
		With autonomic symptoms
		Compound forms
	Partial seizures with complex symptomatology
		With impaired consciousness alone
		With cognitive symptomatology
			With dysmnesic disturbances (conscious amnesia, déjà vu, déjà vécu)
			With ideational disturbances (including “forced thinking”), dreamy state
		With affective symptomatology
		With psychosensory symptomatology
			Illusions (e.g., macropsia, metamorphopsia)
			Hallucinations
		With psychomotor symptomatology: automatisms
		Compound forms
	Partial seizures secondarily generalized
Generalized seizures (bilateral symmetric seizures or seizures without local onset)
	Absences
		Simple absences, with impairment of consciousness only
			Typical, with 3-Hz spike-wave discharge
			Atypical, with fast rhythms or slow spike-waves
		Complex absences, with other phenomena associated with impairment of consciousness; may be typical or atypical as in simple absences
			Myoclonic
			Hypertonic
			Atonic
			Automatic
			Autonomic
		Mixed forms
	Bilateral massive epileptic myoclonus: myoclonic jerks
	Infantile spasms
	Clonic seizures
	Tonic seizures
	Tonic-clonic seizures: grand mal seizures
	Atonic seizures, sometimes associated with myoclonic jerks (myoclonic-atonic seizures) (a) of a very brief duration (epileptic drop attacks); (b) of longer duration (including atonic absences)
	Akinetic seizures
Unilateral or predominantly unilateral seizures
Unclassified epileptic seizures, including all seizures that cannot be classified because of inadequate data

The 1981 revision emphasized that different types of seizure may evolve in temporal succession in the same patient. For instance, a simple partial seizure (which may be motor or which may have cognitive or other psychic manifestations) can be followed by a complex partial one (i.e., with impairment of consciousness), a generalized seizure, or a sequence of both (Overweg et al., 1987; Porter, 1983a). The category of unilateral seizures was dropped from the 1981 revision because these only represented partial seizures with more extensive diffusion. Akinetic seizures and compound, or mixed, seizures were also omitted. The 1981 revision further excluded infantile spasms from the category of generalized seizures. Infantile spasms were considered an epilepsy syndrome, rather than a type of seizure, even though the spasms, which may also occur in older patients, undoubtedly represent a peculiar type of seizure (Egli et al., 1985) with specific electroclinical features.

However, many criticisms have been directed at this scheme (Engel, 2001; Lüders et al., 1993a, 1998; Porter, 1983a). First, as Gloor (1986) emphasized, consciousness is a highly complex concept whose definition
and assessment are extremely difficult. In the glossary appended to the 1981 revision, consciousness was defined as “the degree of awareness and/or responsiveness of the patient to externally applied stimuli.” Responsiveness was defined as “the ability of the patient to carry out simple commands or willed movements,” and awareness as “the patient’s contact with events during the period in question.” These restricted definitions do not consider other important aspects of consciousness such as awareness of “self” or amnesic retention. In the new definitions, the term complex is used to designate those partial seizures that are associated with the impairment of consciousness, whether or not they begin with elementary symptoms (motor or otherwise) or with symptoms previously termed complex. Seizures with dysphasic, dysmnesic, cognitive, and affective manifestations are now classified as simple partial seizures as long as consciousness is not disturbed.

TABLE 2.2. International League Against Epilepsy (1981) revised classification of epileptic seizures

Partial (focal, local) seizures
	Simple partial seizures
		With motor signs: focal, motor, jacksonian, versive, postural, phonatory
		With autonomic symptoms and signs
		With somatosensory or special sensory symptoms (simple hallucinations [e.g., tingling, light flashes, buzzing]): somatosensory, visual, auditory, olfactory, gustatory, vertiginous
		With psychic symptoms (disturbances of higher cerebral functions): dysphasic, dysmnesic, cognitive, affective, illusions, structured hallucinations
	Complex partial seizures (with impairment of consciousness; may sometimes begin with simple symptomatology)
	Simple partial: onset followed by impairment of consciousness
		With simple partial features (A₁-A₄) followed by impaired consciousness
		With automatisms
	Partial seizures evolving to secondarily generalized tonic-clonic (GTC) seizures
		Simple partial seizures evolving to GTC
		Complex partial seizures evolving to GTC
		Simple partial seizures evolving to complex partial seizures, evolving to GTC
Generalized seizures^a
	Absence seizures with impairment of consciousness, with clonic, atonic, tonic, or autonomic components, or with automatisms occurring alone or in combination
	Atypical absences, more pronounced changes of tone than in absence seizures; onset and/or cessation not abrupt
	Myoclonic seizures (single or multiple)
	Clonic seizures
	Tonic seizures
	Tonic-clonic seizures
	Atonic seizures
^aCombinations of the seizures listed here may occur.