Epilepsy: Definitions and Background



Epilepsy: Definitions and Background





I. DEFINITION OF EPILEPSY

Hippocrates recognized epilepsy as an organic process of the brain. However, many ancient writers considered seizures to be the work of supernatural forces. The word epilepsy comes from a Greek word meaning “to be seized by forces from without.”

J. H. Jackson gave direction to the understanding of epilepsy in the late 19th century by carefully analyzing individual cases. From his observations, Jackson (15) formulated the modern definition of epilepsy: “An occasional, excessive, and disorderly discharge of nerve tissue.” Jackson further concluded, “This discharge occurs in all degrees; it occurs with all sorts of conditions of ill health at all ages, and under innumerable circumstances.” His emphasis on the clinical description of a seizure, beginning with the mode of onset, led to the concept of focal epilepsy with subsequent spread of discharging cells.

Epilepsy is a complex symptom caused by a variety of pathologic processes in the brain. It is characterized by occasional (paroxysmal), excessive, and disorderly discharging of neurons that can be detected by clinical manifestations, electroencephalographic (EEG) recording, or both. Paroxysmal discharges of neurons occur when the threshold for firing of the neuronal membranes is reduced beyond the capability of intrinsic membrane-threshold-stabilizing mechanisms to prevent firing (see section VI). The attack may be localized and remain restricted in its focus, or it can spread to other areas of the brain. When the size of the discharging area is sufficient, a clinical seizure occurs; otherwise, the effects may be limited to localized, asymptomatic electrical disturbances. The particular site of the brain affected determines the clinical expression of the seizure. When the synchronized discharges of a neuronal population are recorded by an EEG from the scalp, the paroxysms appear as spikes, slow waves, and spike-wave potentials.

For the patient with epilepsy, the disorder is defined in more personal terms, such as what the patient experiences or recalls about the experience, what others observe and describe, the frequency and duration of attacks, and the impact on self-image and social adjustment.


II. PARTS OF A SEIZURE

The period during which the seizure actually occurs is called the ictus or ictal period. The aura is the earliest portion of a seizure recognized, and the only part remembered by the patient; it may act as a warning. The time immediately after a seizure is referred to as the postictal period. The interval between seizures is the interictal period.



III. TYPES OF EPILEPTIC SEIZURES AND TYPES OF EPILEPSY: CLASSIFICATIONS

Two types of classifications are used for epilepsy: (a) classifications of the epileptic seizures and (b) classifications of the epilepsies. Classifications of epileptic seizures are concerned with classifying each individual seizure as a single event, based on clinical and EEG information. Classifications of the epilepsies are designed to classify syndromes in which the type or types of seizure(s) are one, but not the only, feature of the syndrome. Other features, such as etiology, age at onset, genetics, and evidence of brain pathology, are also included in classifications of the epilepsies.

The classification of epileptic seizures used throughout this book is the 1981 revision of the Clinical and Electroencephalographic Classification of Epileptic Seizures of the International League Against Epilepsy (henceforth, International Classification of Epileptic Seizures) (5). In 2001, the International League Against Epilepsy proposed a new classification of epileptic seizures (6). This proposal has not yet been accepted and is cumbersome in clinical use. The authors have elected to continue use of the approved classification.

In 2001, the International League Against Epilepsy also proposed a revised classification of epilepsies and epileptic syndromes (8) to replace the 1989 revision of the Classification of Epilepsies and Epileptic Syndromes of the International League Against Epilepsy. The 2001 revision has not been approved. However, so many new epilepsy syndromes have been described since 1989 that the authors have elected to use the 2001 classification in this volume.


A. International Classification of Epileptic Seizures

The International Classification of Epileptic Seizures is summarized in Table 1-1 and presented in detail in Table 2-1. Seizures are first classified into two broad categories: (a) partial seizures
(seizure beginning in a relatively small location in the brain) and (b) generalized seizures (seizures that are bilaterally symmetric and without local onset). Seizures are then further classified depending on their exact clinical and EEG manifestations. A summary of the clinical manifestations of the principal types of epileptic seizures recognized by the International Classification of Epileptic Seizures is presented in sections III.A.1-8. For a complete description of the clinical and EEG features of each seizure type, see Chapter 2.








Table 1-1. Summary of international classification of epilepsies







  1. Partial (focal, local) seizures




    1. Simple partial seizures (consciousness not impaired)



    2. Complex partial seizures (temporal lobe or psychomotor seizures; consciousness impaired)



    3. Partial seizures evolving to secondarily generalized seizures [tonic-clonic (grand mal), tonic, or clonic]



  2. Generalized seizures (convulsive or nonconvulsive)




    1. Absence (petit mal) seizures



    2. Myoclonic seizures



    3. Tonic seizures



    4. Atonic seizures



    5. Clonic seizures



    6. Tonic-clonic (grand mal) seizures



  3. Unclassified epileptic seizures (caused by incomplete data)



1. Simple Partial (Focal) Seizures

Simple partial seizures are caused by a local cortical discharge, which results in seizure symptoms appropriate to the function of the discharging area of the brain without impairment of consciousness. Simple partial seizures may consist of motor, sensory, autonomic, or psychic signs or symptoms, or combinations of these (see Chapter 2).


2. Complex Partial (Psychomotor, Temporal Lobe) Seizures

The crucial distinction between simple partial seizures and complex partial seizures is that consciousness is impaired in the latter and not in the former. Impaired consciousness is defined as the inability to respond normally to exogenous stimuli, owing to altered awareness or responsiveness.

At the onset of a complex partial seizure, any of the symptoms or signs (motor, sensory, autonomic, or psychic) of a simple partial seizure may occur without impairment of consciousness, providing an aura. The central feature of the complex partial seizure is impairment of consciousness, which may occur with or without a preceding simple partial aura. No other symptoms or signs may be present during the period of impaired consciousness, or automatisms may appear (i.e., unconscious acts that are “automatic” and of which the patient has no recollection). The attack characteristically ends gradually, with a period of postictal drowsiness or confusion (see Chapter 2).


3. Absence (Petit Mal) Seizures

Absence seizures consist of sudden onset and cessation of impaired responsiveness, accompanied by a unique 3-Hz spike-and-wave EEG pattern. No aura is present, and few or no postictal symptoms occur. The majority of absence seizures last 10 seconds or less and may be accompanied by mild clonic components, atonic or tonic components, automatisms, or autonomic components. Absence seizures usually first manifest between the ages of 5 and 12 years and often stop spontaneously in the teens (see Chapter 2).


4. Myoclonic Seizures

Myoclonic seizures consist of brief, sudden muscle contractions that may be generalized or localized, symmetric or asymmetric, synchronous or asynchronous. No loss of consciousness is usually detectable (see Chapter 2).



5. Tonic Seizures

Tonic seizures consist of a sudden increase in muscle tone in the axial or extremity muscles, or both, producing a number of characteristic postures. Consciousness is usually partially or completely lost. Prominent autonomic phenomena occur. Postictal alteration of consciousness is usually brief, but it may last several minutes. Tonic seizures are relatively rare and usually begin between 1 and 7 years of age (see Chapter 2).


6. Atonic Seizures

Atonic seizures consist of sudden loss of muscle tone. The loss of muscle tone may be confined to a group of muscles, such as the neck, resulting in a head drop. Alternatively, atonic seizures may involve all trunk muscles, leading to a fall to the ground (see Chapter 2).


7. Clonic Seizures

Clonic seizures occur almost exclusively in early childhood. The attack begins with loss or impairment of consciousness associated with sudden hypotonia or a brief, generalized tonic spasm. This is followed by 1 minute to several minutes of bilateral jerks, which are often asymmetric and may appear predominantly in one limb. During the attack, the amplitude, frequency, and spatial distribution of these jerks may vary greatly from moment to moment. In other children, particularly those aged 1 to 3 years, the jerks remain bilateral and synchronous throughout the attack. Postictally, recovery may be rapid, or a prolonged period of confusion or coma may ensue (see Chapter 2).


8. Tonic-Clonic (Grand Mal) Seizures

Before the tonic phase of a tonic-clonic seizure, bilateral jerks of the extremities or focal seizure activity may occur. The onset of the seizure is marked by loss of consciousness and increased muscle tone (tonic phase), which usually results in a rigid, flexed posture at first, and then a rigid, extended posture. This is followed by bilateral rhythmic jerks that become further apart (clonic phase). Prominent autonomic phenomena are observable during the tonic and clonic phases. In the postictal phase, increased muscle tone occurs first, followed by flaccidity. Incontinence may occur. The patient awakens by passing through stages of coma, confusional state, and drowsiness (see Chapter 2).


B. International Classification of Epilepsies

The International Classification of Epilepsies (Table 1-2) begins by dividing epilepsies according to overall seizure type: generalized or focal. Generalized epilepsies involve seizures with initial activation of neurons in both cerebral hemispheres, whereas focal epilepsies involve seizures with initial activation of a group of neurons within one hemisphere. Note that the terms focal, localization-related, partial, and local are often used synonymously.

Epilepsies are next divided according to etiology: idiopathic, symptomatic, or familial. Idiopathic means arising spontaneously from an obscure or unknown cause. Symptomatic epilepsies arise as symptoms of a known brain abnormality. Familial means arising from a known gene defect. Three special categories also are used: reflex epilepsies, epileptic encephalopathies, and progressive myoclonic epilepsies. Finally, some conditions may result in seizures but are not likely to result in epilepsy: chronic unprovoked seizures.









Table 1-2. An example of a classification of epilepsy syndromes





























































































































































Groups of Syndromes

Specific Syndromes


Idiopathic focal epilepsies of infancy and childhood

Benign infantile seizures (nonfamilial)

Benign childhood epilepsy with centrotemporal spikes

Early-onset benign childhood occipital epilepsy (Panayiotopoulos type)

Late-onset childhood occipital epilepsy (Gastaut type)


Familial (autosomal dominant) focal epilepsies

Benign familial neonatal seizures

Benign familial infantile seizures

Autosomal dominant nocturnal frontal lobe epilepsy

Familial temporal lobe epilepsy

Familial focal epilepsy with variable foci


Symptomatic (or probably symptomatic) focal epilepsies

Limbic epilepsies

Mesial temporal lobe epilepsy with hippocampal sclerosis


Mesial temporal lobe epilepsy defined by specific etiologies


Other types defined by location and etiology

Neocortical epilepsies


Rasmussen syndrome


Hemiconvulsion-hemiplegia syndrome


Other types defined by location and etiology


Migrating partial seizures of early infancy


Idiopathic generalized epilepsies

Benign myoclonic epilepsy in infancy

Epilepsy with myoclonic astatic seizures

Childhood absence epilepsy


Epilepsy with myoclonic absences

Idiopathic generalized epilepsies with variable phenotypes


Juvenile absence epilepsy


Juvenile myoclonic epilepsy


Epilepsy with generalized tonic-clonic seizures only

Generalized epilepsies with febrile seizures plus (GEFS+)


Reflex epilepsies

Idiopathic photosensitive occipital lobe epilepsy

Other visual-sensitive epilepsies

Primary reading epilepsy

Startle epilepsy


Epileptic encephalopathies (in which the epileptiform abnormalities may contribute to progressive dysfunction)

Early myoclonic encephalopathy


Ohtahara syndrome


West syndrome


Dravet syndrome (previously known as severe myoclonic epilepsy in infancy)

Myoclonic status in non-progressive encephalopathies

Lennox-Gastaut syndrome

Landau-Kleffner syndrome

Epilepsy with continuous spike waves during slow-wave sleep


Progressive myoclonus epilepsies

See specific diseases


Seizures not necessarily requiring a diagnosis of epilepsy

Benign neonatal seizures


Febrile seizures


Reflex seizures

Alcohol-withdrawal seizures

Drug or other chemically induced seizures

Immediate and early posttraumatic seizures

Single seizures or isolated clusters of seizures

Rarely repeated seizures (oligoepilepsy)


From Engel J Jr. A proposed diagnostic scheme for people with epileptic seizures and with epilepsy: report of the ILAE Task Force on Classification and Terminology. Epilepsia 2001;42:796-803, with permission.



Based on these categories, the epilepsies are divided into eight groups (Table 1-2), within each of which are a number of specific epilepsy syndromes based on specific clustering of seizure type(s), specific etiology, genetics, age, and evidence of brain pathology
(Table 1-2

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Jun 17, 2016 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Epilepsy: Definitions and Background

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