Classification of Seizure Disorders (Stereotactic and Functional Neurosurgery)


An epileptic seizure is a behavioral event that is caused by an abnormal neuronal discharge. Epilepsy refers to the condition of recurrent seizure. Certain metabolic or medical conditions, including hypoglycemia, hypona-tremia, and alcohol withdrawal may predispose an individual to a single seizure, but not recurrent seizures (epilepsy). In the United States, epilepsy affects approximately 6% of the population. Approximately 4% of individuals living to age 75 may experience a single unprovoked seizure, and if provoked seizures are included, the incidence approaches 10% [1].

It is important to classify seizure disorders. Anticonvulsant treatment differs for the various seizure types, and before initiating a treatment plan, seizure type must be classified. For example, certain generalized seizures respond best to valproate, and control may be aggravated by certain gaba-nergic drugs, including gabapentin. The type of seizure may influence the patient’s ability to work, and different seizure types have different natural histories. Accurate classification helps with prognostication.

Currently, there is both a seizure and an epilepsy classification. In 1981, the International League Against Epilepsy (ILAE) developed a descriptive classification of seizures that used both the electroencephalogram (EEG) and clinical symptoms to define the seizure type (Table 1) [2]. The Classification of Epilepsies and Epileptic Syndromes of the International League Against Epilepsy, developed in 1989, incorporates etiological, biological, and genetic considerations [3]. This topic will concentrate on the former descriptive classification of epileptic seizures.

Table 1 ILAE Classification of Epileptic Seizures


Partial (focal) seizures.


Simple partial seizures (consciousness not impaired)

1. With motor signs (examples include a jacksonian march, loss of tone, versive movements)

2. With sensory symptoms (examples include visual, auditory, somatosensory, olfactory, and gustatory symptoms)

3. With psychic symptoms (involves a disturbance of higher cortical functions, eg, deja vu, hallucinations, and aphasia)

4. With autonomic symptoms (examples include epigastric sensations, flushing, piloerection, pupillary changes)


Complex partial seizures (consciousness is impaired)

1. With simple partial onset followed by impaired consciousness

2. With impairment of consciousness at the onset

3. Impairment of complex partial seizures with automatisms


Partial seizures evolving to secondary generalized seizures

1. Simple partial seizures evolving to generalized seizures

2. Complex partial seizures evolving to generalized seizures

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


Generalized seizures (no focal onset, convulsive or nonconvulsive)


Absence seizures

1. With impaired consciousness

2. Impaired consciousness with additional features including atonic or tonic activity, automatisms.


Myoclonic seizures characterized by single or multiple jerks


Tonic-clonic seizures


Tonic seizures


Atonic seizures


Clonic seizures


Unclassified epileptic seizures

The principle feature of the seizure classification is to determine whether seizures started focally (partial seizures) or have a diffuse onset (generalized seizures). It is usually possible to make this distinction from an accurate history, but certain focal seizures spread very rapidly, and it may not be possible to make this distinction. If a focal onset is determined, the next issue is to establish whether there is an alteration in consciousness. If consciousness is not affected, seizures are classified as simple partial seizures. Conversely, if consciousness is altered, seizures are classified as complex partial seizures. Generalized seizures are divided according to their motor characteristics. It is important to determine whether the subject experienced predominantly tonic, tonic-clonic, or generalized motor activity.

Classifying seizures depends on an understanding of neuroanatomy. The initial clinical symptom, or aura, is extremely helpful to localize seizure onset. For example, visual hallucinations suggest occipital onset, whereas a deja vu feeling suggests temporal lobe onset. Patients with partial seizures may not report an aura if (1) the seizure spreads rapidly and generalizes, and consciousness is rapidly altered, (2) the individual is amnestic after the seizure (3), seizures begin in a clinically silent cortical region. Examples of ”silent” areas include certain frontal and association cortical regions.

Partial Seizures

When onset is focal, seizures are referred to as partial seizures, but the term focal is still used. Partial seizures occur when electrical activation begins in a localized region of one cerebral hemisphere. Partial seizures are classified primarily on the basis of whether consciousness is altered. When consciousness is preserved, seizures are referred to as simple partial seizures. When consciousness is altered or impaired, seizures are classified as complex partial seizures. If the electrical discharge spreads to involve deep subcortical structures, a partial seizure will evolve to a secondary generalized seizure.

Simple Partial Seizures

Simple partial seizures result when the ictal discharge remains localized to a restricted cortical region within one hemisphere and does not spread to the opposite hemisphere. The electrical changes may not be seen on surface EEG. Because electrical spread is limited, there is no alteration in consciousness, and the clinical manifestations will depend on the properties of the activated cortical region. Most simple partial seizures can be grouped into four clinical groups: motor, sensory psychic, and autonomic.

Simple motor seizures involve an electrical discharge activating the motor cortex. Patients will typically experience contralateral clonic activity that may be localized or spread. Focal motor seizures may be predominantly versive with contraversive head turning. When the motor activity spreads, it is referred to as a jacksonian march. Focal motor activity does not usually exceed 60 seconds. After a focal motor seizure, patients may experience transient weakness, which is referred to as a Todd’s paralysis. The paralysis may lasts minutes to hours, and the clinician needs to differentiate a Todd’s paralysis from a stroke. Focal motor activity may be very localized, and may persist hours to days. These seizures are referred to as epilepsia partialis continua.

Seizures occurring with activation of the sensory cortex produce so-matosensory seizures. Clinical features reported include pins and needles, numbness, novocaine-type tingling, and the sensory symptoms commonly march. Involvement of the visual cortex may present with elementary or elaborate visual hallucinations. Activation of the primary visual cortex is accompanied by simple, elementary visual hallucinations, such as flashing lights, sparkles, and colors. When the association visual cortex is involved, visual symptomatology is complex, and patients may report complex shapes, illusions, and distortions. The occipital cortex has direct frontal connections, and the initial clinical manifestations may be tonic eye deviation and blinking. Involvement of the auditory cortex usually produces simple auditory hallucinations, including tinnitus and buzzing sensations. Complex auditory hallucinations, such as a fixed music tune are less common, and when patients report hearing voices, the etiology is usually psychiatric and not neurological. With activation of the temporal region, simple partial seizures may present with gustatory or olfactory sensations.

Simple partial seizures with psychic symptoms usually progress to complex partial seizures leading to impairment of consciousness. These seizures are associated with a disturbance of higher cortical function. Symptoms include aphasia, visual illusions, and complex structured hallucinations. Patients often complain of a deja vu experience. Affective symptoms include fear and anger.

Autonomic symptoms may be the most prominent seizure manifestation. A common autonomic symptom is a rising epigastric sensation and is associated with a temporal lobe seizure focus. Flushing, sweating, piloerec-tion, pupil dilatation, and incontinence may occur as simple partial seizures.

Complex Partial Seizures

During a seizure, it is important to determine whether the subject experiences an alteration or loss of consciousness. This implies spread of the epileptic discharge across the corpus callosum to the opposite hemisphere. Patients may describe a subjective feeling or aura before losing consciousness. If the epileptic discharge does not progress, the aura constitutes the simple partial seizure. Common temporal lobe auras include a rising epigastric sensation, fear, deja vu, jamais vu, and a feeling of detachment. Alteration of consciousness has important clinical relevance, and patients should not drive, operate heavy machinery, or partake in certain sporting activities unsupervised. Complex partial seizures may be clinically bland, and it is not always possible to determine whether consciousness was impaired. At most epilepsy centers, nurses are trained to question patients during a seizure to determine whether the patient can learn and incorporate new information. Failure to follow simple instructions (ictal unresponsiveness) implies loss of consciousness. It is extremely difficult to determine whether consciousness is affected in neonates and young children. After a complex partial or generalized seizure, patients are amnestic and confused, and the postictal state may last minutes to hours. Without EEG monitoring, it is not possible to determine the transition from the ictal to the postictal state.

During a complex partial seizures, patients may carry out ”automatic” behaviors or motor activities, referred to as automatisms. An automatism may be the continuation of an activity that preceded the onset of the seizure. Common automatisms include eating movements (lipsmacking, chewing, and swallowing), simple or elaborate gestures, verbal automatisms consisting of forced ictal speech, and ambulatory automatisms. Gestures include fumbling with objects and picking at one’s clothes, and patients are unaware of these behaviors. Oropharyngeal and gustatory automatisms are usually associated with seizure spread to the insula and amygdala. Automatisms may occur with a prolonged generalized absence seizure, and the EEG differentiates between these two seizure types. Both simple and partial complex seizures may rapidly evolve to a generalized tonic-clonic seizure and are referred to as secondary generalized seizures. The majority (70%-80%) of partial complex seizures arise from the temporal lobe, followed by the frontal lobe.

First-line anticonvulsants for simple and complex partial seizures with or without generalization are carbamazepine, phenytoin, and valproic acid. Adjunctive agents include gabapentin, lamotrigine, tiagabine, and topi-ramate.

Generalized Seizures

Generalized seizures are characterized by an abrupt loss of consciousness. Generalized seizures with motor activity include tonic-clonic seizures, my-oclonic seizures, tonic, or clonic seizures. Generalized seizures without motor activity includes absence and atonic seizures. Generalized seizures frequently have a genetic basis, and it is important to ask about a family history. The type of generalized seizure is age dependent. Absence seizures occur in children younger than age 10, myoclonic seizures present later in the teenage years, and tonic clonic seizures typically begin in the teens. The typical EEG pattern associated with generalized seizures is a generalized spike or polyspike and slow wave discharge. In contrast, partial seizures (with or without secondary generalization) is associated with focal EEG abnormalities, including focal spike discharges, and focal slowing.

Absence Seizures

The essential feature of an absence seizure is the sudden, abrupt loss of consciousness. Seizure onset is characterized by immediate behavioral arrest, and patients are noted to have a brief motionless stare. An absence seizure typically lasts several seconds, but may last up to 30 seconds. Speech is interrupted momentarily, and the subject will then resume speaking. The attack may be influenced by sensory input, and may terminate when the individual is spoken to.

Absence seizures occur in those with a strong family history. Symptomatic children will show the classic generalized three per second spike and wave pattern, but the EEG of asymptomatic siblings may show a similar spike and wave. The course of absence seizures is variable, and absence seizures usually remit by mid-adolescence. Rarely, absence seizures will persist, and children may subsequently develop myoclonic or tonic-clonic seizures in their teenage years.

The sole manifestation of an absence seizure may be loss of consciousness with no other activity. Additional clinical features frequently accompany absence seizures. During the attack, myoclonic movements, which commonly involve eyelid fluttering or facial twitching, may occur.

Additional manifestations include atonic components. Examples are brief loss of neck and postural tone, leading to drooping of the head or slumping of the body. When diminution in tone is severe, the subject may fall. If the absence seizure is prolonged for more than 15 seconds, patients may exhibit simple or elaborate automatisms similar to the automatisms seen during complex partial seizures. An absence seizure with automatisms will have an EEG with the classic generalized spike and wave pattern. The treatment of choice for absence seizures is ethosuximide.

Myoclonic Seizures

Myoclonic seizures usually begin during the early teenage years. A my-oclonic jerk is a brief shock-like contraction of an individual muscle or a muscle group. These jerks usually involve the limbs but may be confined to the face or trunk. Generalized myoclonic jerks or jerks involving the legs can be disabling, because they are associated with violent falls and frequent fractures. Myoclonic seizures have a circadian pattern and commonly occur in the morning shortly after awakening. Patients may drop or throw objects held in their hands. Myoclonic seizures are very brief, lasting approximately 1 second, and the EEG during the myoclonic jerk will show a generalized spike or polyspike and slow wave discharge. A flurry of myoclonic seizures may evolve to a generalized tonic-clonic seizure.

It is important to emphasize that not all myoclonus is epileptic. Myo-clonic jerks may occur with focal spinal disease or inherited degenerative diseases. The treatment of choice for myoclonic seizures is valproate. Alternative effective anticonvulsants include lamotrigine and topirimate.

Tonic-Clonic Seizures

This is the most commonly encountered generalized seizure and is also referred to as a grand mal seizure or convulsion. Generalized seizures may occur in either childhood or adult life, and are often preceded by a flurry of myoclonic seizures. Typically, no warning precedes the seizure, although patients may complain of vague premonitions (examples include nervousness or irritability) minutes to hours before the seizure. Abrupt tonic contractions of muscles result in the patient falling to the ground in a tonic state, which may result in injury. Sustained contractions of the respiratory muscles result in stridor and a loud moan. Patients are rigid during the tonic phase, and cyanoses may occur. Patients may bite their tongue or become incontinent. The tonic phase typically lasts 30 seconds and is followed by clonic motor activity lasting 60 to 90 seconds. Shallow breathing may occur, and patients are at a risk for aspiration. The clonic phase is followed by deep sighing respiration, muscles are hypotonic, and the gag reflex is reduced, increasing the risk for aspiration. Patients may remain unresponsive for minutes to hours after a tonic-clonic seizure, and then go into a deep sleep. Patients may be amnestic for several hours after a tonic-clonic seizure (similar to the amnesia after electroconvulsive shock therapy). Sustained muscle contractions result in painful muscles and fatigue, and severe headaches are common. Patients may experience rib and vertebral fractures, and elderly women with osteoporosis are especially vulnerable. It is important to determine whether the tonic-clonic seizure was secondary generalized or occurred with no prior aura. Focal onset will suggest a structural brain lesion. Partial seizures may spread rapidly and may be difficult to distinguish from primary generalized seizures. An EEG is helpful in distinguishing between these two seizure types. Primary generalized seizures have a generalized spike and wave pattern, and they respond to valproate. Secondary generalized seizures are associated with focal interictal spikes and respond to those drugs used to treat complex partial seizures.

Absence, myoclonic, and tonic-clonic seizures are the common generalized seizure types, but generalized atonic clonic and tonic seizures do occur. Atonic seizures are very disabling, and patients experience frequent drop attacks, leading to severe injuries and bone fractures. Patients with atonic seizures need to wear a helmet to prevent severe head injuries. Atonic seizures are brief, and consciousness may be lost. Tonic seizures are also brief, and are associated with violent muscle contractions, and extensor posturing. The head and eyes may deviate, and the body may rotate. Generalized seizures may not have a tonic component, and may present as generalized clonic seizures, consisting of repetitive generalized clonic jerks. Tonic and atonic seizures do not have a familial inheritance component. These two seizure types usually occur in patients with severe underlying brain disease and are very refractory to anticonvulsants. When standard anticonvulsant therapy fails, patients may need more invasive treatments, including a corpus callosotomy or vagal nerve stimulation.

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