Classification

How best to classify epileptic seizures and epileptic syndromes has occupied epileptologists for centuries. In the middle of the 19th century the epilepsy literature was dominated by psychiatrists who tried to systematize epilepsy based on their experiences with chronic patients in asylums. They spent more time on the psychopathological classification of psychiatric symptoms in epilepsy than on describing epileptic seizures. Specific psychiatric syndromes, especially short-lasting episodic psychoses and mood disorders, were regarded as being of equal diagnostic significance for epilepsy as convulsions.

With the introduction of electroencephalography (EEG) in the 1930s many episodic psychiatric states were identified as nonepileptic in origin. Epileptic seizures, however, showed very different ictal EEG patterns. Since then, epileptologists have concentrated on the electroclinical differentiation of epileptic seizures. Problems of terminology became obvious with increasing communication between international epi-leptologists in the middle of the 20th century. The first outlines of international classifications of epileptic seizures and epileptic syndromes were published in 1970. The proposed classifications by the Commission on Classification and Terminology of the International League against Epilepsy (ILAE) from 1981 and 1989 (Tables I and II) are based on agreements among international epileptologists and compromises between various viewpoints. They must not be regarded as definitive; a revision is currently being developed.

delineation of disturbance of function, and pathological confirmation. In the 20th century clinical events could be linked to ictal electroencephalographic findings. More detailed analysis of seizures became possible with simultaneous EEG video monitoring and ictal neuropsychological testing. In the former, patients are monitored by video cameras and continuous EEG recordings for prolonged periods. The data can be simultaneously displayed on a split-screen television monitor (Fig. 1).

The International Classification of Epileptic Seizures (ICES) from 1981 is based on this improved monitoring capability, which has permitted more accurate recognition of seizure symptoms and their longitudinal evolution. The current classification of seizures is clinically weighted and gives no clear definitions in terms of seizure origin. The ICES does not reflect our most recent understanding of the localizing significance of specific seizure symptoms, which has grown significantly since 1981 due to increased data from intensive monitoring and epilepsy surgery. Some parts of the ICES are therefore outdated and in need of revision. Complex focal seizure types, for example, are not yet distinguished according to a probable origin in the frontal or the temporal lobe.

The principal feature of the ICES is the distinction between seizures that are generalized from the beginning and those that are partial or focal at onset and may or may not evolve to secondary generalized seizures (Table I). In generalized seizures there is initial involvement of both hemispheres, reflecting an epileptogenic generator in subcortical structures. Consciousness may be impaired and this impairment may be the initial manifestation. Motor manifestations are bilateral. The ictal EEG patterns are initially bilateral. Spikes, spike-wave complexes, and polyspike-wave complexes are all typical (Fig. 2).

Focal seizures are those in which the first clinical and EEG changes indicate initial activation of a system of neurons limited to a part of one cerebral hemisphere. The other important feature of the ICES is the separation between simple and complex partial seizures depending on whether there is preservation or impairment of consciousness.

A. Classification of Seizures

Most authors in the 19th century simply differentiated seizures according to severity ("petit mal'' and "grand mal''). Hughlings Jackson was the first to recognize the need for an anatomical description, physiological

B. Classification of Syndromes

"Epilepsy is the name for occasional sudden, excessive, rapid, and local discharges of the gray matter.'' This simple definition was formulated by Jackson in 1866

Table I

International Classification of Epileptic Seizures'

Clinical seizure type

Ictal EEG

Focal (partial, local) seizures

A. Simple partial seizures

Local contralateral discharge starting over corresponding area of cortical representation (not always recorded on the scalp)

1. With motor symptoms a. Focal motor without march b. Focal motor with march (Jacksonian)

c. Versive d. Postural e. Phonatory (vocalization or arrest of speech)

2. With somatosensory or special sensory symptoms (simple hallucinations, e.g., tingling, light flashes, and buzzing)

a. Somatosensory b. Visual c. Auditory d. Olfactory e. Gustatory f. Vertiginous

3. With autonomic symptoms or signs (including epigastric sensation, pallor, sweating, flushing, piloerection, and pupillary dilatation)

4. With psychic symptoms (disturbance of higher cortical function); these symptoms rarely occur without impairment of consciousness and are much more commonly experienced as complex partial seizures.

c. Cognitive (e.g., dreamy states and distortions of time sense)

e. Illusions (e.g., macropsia)

f. Structured hallucinations (e.g., music and scenes)

B. Complex focal seizures (with impairment of consciousness; may Unilateral or frequently bilateral discharge; diffuse or sometimes begin with simple symptomatology) focal in temporal or frontotemporal regions

1. Simple partial onset followed by impairment of consciousness a. With simple partial features (as in A, 1-4) followed by impaired consciousness b. With automatisms

2. With impairment of consciousness at onset a. With impairment of consciousness only b. With automatisms

C. Focal seizures evolving to secondarily generalized seizures (this may be Above discharge becomes secondarily and rapidly generalized tonic-clonic, tonic, or clonic) generalized

1. Simple partial seizures (A) evolving to generalized seizures

2. Complex partial seizures (B) evolving to generalized seizures

3. Simple focal seizures evolving to complex focal seizures evolving to generalized seizures

(continues)

Table I (continued)

Clinical seizure type Ictal EEG

Generalized seizures

A. Absence seizures

1. Absence seizures a. Impairment of consciousness only b. With mild clonic components c. With atonic components d. With tonic components e. With automatisms f. With autonomic components

2. Atypical absence a. Changes in tone that are more pronounced than in A.1

b. Onset and/or cessation that is not abrupt

B. Myoclonic seizures, myoclonic jerks (single or multiple)

C. Clonic seizures

D. Tonic seizures

E. Tonic-clonic seizures

Usually regular and symmetrical 3-Hz but may be 2-4 Hz spike and slow-wave complexes and may have multiple spike and slow-wave complexes; abnormalities are bilateral

F. Atonic seizures

EEG more heterogeneous; may include irregular spike and slow-wave complexes, fast activity, or other paroxysmal activity; abnormalities are bilateral but often irregular and asymmetric

Polyspike and wave, or sometimes spike and wave or sharp and slow waves

Fast activity (10 c/sec or more) and slow waves; occasional spike and wave patterns

Low-voltage, fast activity or a fast rhythm of 9-10 c/ sec or more, decreasing in frequency and increasing in amplitude

Rhythm at 10 or more c/sec decreasing in frequency and increasing in amplitude during tonic phase, interrupted by slow waves during the clonic phase

Polyspikes and wave or flattering or low-voltage fast activity

"From the Commission on Classification and Terminology of the International League against Epilepsy (1981).

long before the introduction of electroencephalography. It has not lost its justification today. Recurrent epileptic seizures are pathognomonic for all types of epilepsies. The clinical spectrum of epilepsy, however, is much more complex and an epileptic syndrome is characterized by a cluster of signs and syndromes customarily occurring together; these include such features as type of seizure, etiology, structural lesions, precipitating factors, family history, age of onset, severity, chronicity, diurnal and circadian cycling, and prognosis.

In contrast to a syndrome, a disease is characterized by a specific etiology and prognosis. Some recognized entities in the International Classification of Epilepsies and Epileptic Syndromes (ICEES) are diseases and others are syndromes, some of which may turn out to be diseases—a specific etiology may still be discovered.

The ICEES distinguishes generalized and localization-related (focal, local, and partial) epilepsies. Generalized epilepsies are syndromes characterized by generalized seizures in which there is involvement of both hemispheres from the beginning of the seizure. Seizures in localization-related epilepsies start in a circumscribed region of the brain. The other important classification criterion refers to etiology. The ICEES distinguishes idiopathic, symptomatic, and crypto-genic epilepsies. Idiopathic means that a disease is not preceded or occasioned by another. The major pathogenetic mechanism is genetic predisposition. Symptomatic epilepsies and syndromes are considered the consequence of a known or suspected disorder of the central nervous system. In cryptogenic disorders, a cause is suspected but remains obscure, often due to limited sensitivity of diagnostic techniques.

Table II

International Classification of Epilepsies and Epileptic Syndromes0

Localization-related (focal, local, and partial) epilepsies and syndromes

Idiopathic (with age-related onset)

Currently, the following syndromes are established, but more may be identified in the future:

Benign childhood epilepsy with centrotemporal spikes

Childhood epilepsy with occipital paroxysms

Primary reading epilepsy

Symptomatic

Chronic progressive epilepsia partialis continua of childhood (Kozhevnikov's syndrome)

Syndromes characterized by seizures with specific modes of precipitation

Temporal lobe epilepsy

With amygdala-hippocampal seizures

With lateral temporal seizures

Frontal lobe epilepsy

With supplementary motor seizures

With cingulate seizures

With seizures of the anterior frontopolar region With orbitofrontal seizures With dorsolateral seizures With opercular seizures With seizures of the motor cortex Parietal lobe epilepsies Occipital lobe epilepsies Generalized epilepsies and syndromes

Idiopathic, with age-related onset, listed in order of age Benign neonatal familial convulsions Benign neonatal convulsions Benign myoclonic epilepsy in infancy Childhood absence epilepsy (pyknolepsy) Juvenile absence epilepsy

Juvenile myoclonic epilepsy (impulsive petit mal) Epilepsy with grand mal seizures (GTCS) on awakening Other generalized idiopathic epilepsies not defined previously Epilepsies precipitated by specific modes of activation Cryptogenic or symptomatic (in order of age) West syndrome (infantile spasms, Blitz-Nick-Salaam Krampfe)

Lennox-Gastaut syndrome Epilepsy with myoclonic-astatic seizures Epilepsy with myoclonic absences Symptomatic Nonspecific etiology

(continues)

(continued)

Early myoclonic encephalopathy

Early infantile epileptic encephalopathy with suppression burst

Other symptomatic generalized epilepsies not defined previously Specific syndromes Epileptic seizures may complicate many disease states. Under this heading are included diseases in which seizures are a presenting or predominant feature. Epilepsies and syndromes undetermined as to whether they are focal or generalized

With both generalized and focal seizures Neonatal seizures

Severe myoclonic epilepsy in infancy

Epilepsy with continuous spike waves during slow-wave sleep Acquired epileptic aphasia (Landau-Kleffner syndrome) Other undetermined epilepsies not defined previously Without unequivocal generalized or focal features

"From the Commission on Classification and Terminology of the International League against Epilepsy (1989).

1. Localization-Related Epilepsies and Syndromes

Seizure symptomatology and ictal EEG findings are the most important criteria for anatomical classification of localization-related epilepsies. As mentioned, the 1981 version of the ICES, with its emphasis on the formal structure of seizures, is of limited help in the detailed localization of seizures required in the ICEES from 1989. The 1989 classification has been criticized because reliable localization often requires invasive EEG techniques. It is hoped that with more data from taxonomic studies, clinical symptoms or symptom clusters will be identified that eventually will allow classification on clinical grounds in most cases.

Temporal lobe epilepsies are classified as those with lateral temporal seizures with auditory hallucinations, language disorders (in the case of dominant hemisphere focus) or visual illusions, and those with amygdala-hippocampal (mesiobasal limbic or rhinen-cephalic) seizures. The latter are characterized by simple seizure symptoms, such as increasing epigastric discomfort, nausea, marked autonomic signs, and other symptoms including borborygmi, belching, pallor, fullness of the face, flushing of the face, arrest of respiration, pupillary dilatation, fear, panic, and

Figure 1 Video recording of a complex partial seizure with secondary generalization (frontal lobe epilepsy): (a) interictal normal behavior; (b) patient pushes alarm button; (c) patient describes aura of fear; (d) automatisms: hand rubbing; (e) alternating tapping of legs; (f) patient does not respond when asked to name a pair of glasses; (g) tonic elevation of right arm; (h) generalized myoclonic movements; (i) reorientation; (j) end of seizure, patient answers adequately.

Figure 1 Video recording of a complex partial seizure with secondary generalization (frontal lobe epilepsy): (a) interictal normal behavior; (b) patient pushes alarm button; (c) patient describes aura of fear; (d) automatisms: hand rubbing; (e) alternating tapping of legs; (f) patient does not respond when asked to name a pair of glasses; (g) tonic elevation of right arm; (h) generalized myoclonic movements; (i) reorientation; (j) end of seizure, patient answers adequately.

Figure 2 EEG in idiopathic generalized epilepsy (juvenile myoclonic epilepsy) with generalized polyspike-wave pattern.

olfactory hallucinations. Complex focal seizures often begin with a motor arrest, typically followed by oroalimentary automatisms. The duration is typically more than 1 min and consciousness recovers gradually.

Frontal lobe epilepsies are characterized by seizures of short duration, minimal or no postictal confusion, rapid secondary generalization, vocalization, prominent motor manifestations that are tonic or postural, complex gestural automatisms, and nocturnal clustering. Ictal scalp EEGs may show bilateral or multilobar discharges or are often normal. Accurate localization of frontal lobe epilepsies may therefore be difficult.

2. Generalized Epilepsies and Syndromes

Idiopathic generalized epilepsies are characterized by an age-related onset that reflects the ability of the brain to produce certain seizure types depending on cerebral maturation. In general, patients are asymptomatic between seizures. Radiological investigations are negative. Frequently, there is an overlap of idiopathic generalized epilepsies, especially of those manifesting in later childhood and adolescence. Response to antiepileptic drug treatment and psychosocial prognosis are good.

Symptomatic generalized epilepsies and syndromes usually start in infancy or early childhood. In most children several seizure types occur. EEG discharges are less rhythmical and less synchronous than in idiopathic generalized epilepsies. There are neurological, neuropsychological, and radiological signs of diffuse cerebral disease. The only difference between cryptogenic and symptomatic syndromes is that in cryptogenic syndromes the presumed cause cannot be identified.

3. Epilepsies and Syndromes Undetermined as to Whether They Are Focal or Generalized

There are two groups of patients who cannot be classified as focal or generalized. The first group consists of patients with both generalized and focal seizures (e.g., patients with both focal seizures and absence seizures). The second group comprises patients without unequivocal generalized or focal features (e.g., patients with nocturnal generalized tonic-clonic seizures).

4. Specific Syndromes

These are isolated seizures and situation-related syndromes, such as febrile seizures and seizures occurring only when there is an acute metabolic or toxic event due to factors such as alcohol, drugs, eclampsia, or hyperglycemia.

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