Epilepsy classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Vishnu Vardhan Serla M.B.B.S. [2]

Classification

Epilepsies are classified five ways:

1. By their first cause (or etiology).
2. By the observable manifestations of the seizures, known as semiology.
3. By the location in the brain where the seizures originate.
4. As a part of discrete, identifiable medical syndromes.
5. By the event that triggers the seizures, as in primary reading epilepsy.

In 1981, the International League Against Epilepsy (ILAE) proposed a classification scheme for individual seizures that remains in common use. This classification is based on observation (clinical and EEG) rather than the underlying pathophysiology or anatomy and is outlined later on in this article. In 1989, the ILAE proposed a classification scheme for epilepsies and epileptic syndromes. This can be broadly described as a two-axis scheme having the cause on one axis and the extent of localisation within the brain on the other. Since 1997, the ILAE have been working on a new scheme that has five axes: ictal phenomenon, seizure type, syndrome, etiology and impairment.

Seizure types

Main article: Seizure types

Seizure types are organized firstly according to whether the source of the seizure within the brain is localized (partial or focal onset seizures) or distributed (generalized seizures). Partial seizures are further divided on the extent to which consciousness is affected. If it is unaffected, then it is a simple partial seizure; otherwise it is a complex partial (psychomotor) seizure. A partial seizure may spread within the brain - a process known as secondary generalization. Generalized seizures are divided according to the effect on the body but all involve loss of consciousness. These include absence (petit mal), myoclonic, clonic, tonic, tonic-clonic (grand mal) and atonic seizures.

Seizure Syndromes

There are many different epilepsy syndromes, each presenting with its own unique combination of seizure type, typical age of onset, EEG findings, treatment, and prognosis. Below are some common seizure syndromes:

Seizure Syndromes

Type of seizure	Typical age of onset	Description	EEG findings	Prognosis	Treatment
Infantile spasms (West syndrome)	Affects infants (30 days to 1 year of life)	Characterized by sudden flexor and extensor spasms of head, trunk, and extremities Associated with brain development abnormalities, tuberous sclerosis and perinatal insults to the brain	Hypsarrhythmia, or a high-voltage slow wave with multifocal spikes Generalized 3 Hz spike and wave discharges in EEG	Poor prognosis (more than two-thirds will have severe deficits)	First line treatment is adrenocorticotropic hormone (ACTH or corticotropin) Vigabatrin is particularly effective when tuberous sclerosis is the cause of seizures
Childhood absence epilepsy	Affects children between the ages of 4 and 12 years of age	These patients have recurrent absence seizures that can occur hundreds of times a day A subset of these patients will also develop generalized tonic-clonic seizures	Stereotyped generalized 3 Hz spike and wave discharges	Fairly good prognosis, these children do not usually show cognitive decline or neurological deficits	First line treatment for pure absence seizures is ethosuximide If patients do not respond or have mixed seizures along with their absence seizures, then valproic acid can be used
Dravet's syndrome Severe myoclonic epilepsy of infancy (SMEI)	Onset in first year of life Symptoms peak at about 5 months of age with febrile hemiclonic or generalized status epilepticus	Boys twice as often affected as girls Most cases are sporadic Family history of epilepsy and febrile convulsions is present in around 25 percent of the cases, but familial cases are exceptionnal This very rare syndrome is delimitated from benign myoclonic epilepsy by its severity and must be differentiated from the Lennox-Gastaut syndrome and Doose’s myoclonic-astatic epilepsy. From: www.dravet.com	---------	Prognosis is poor	---------
Benign focal epilepsies of childhood	Benign rolandic epilepsy begins in children between the ages of 3 and 16 years	The most common syndromes comprising the benign focal epilepsies of childhood include Benign Childhood Epilepsy with Centro-Temporal Spikes (or benign rolandic epilepsy), and Benign Childhood Epilepsy with Occipital Paroxysms. Seizures typically occur at night, and are brief, focal motor events affecting facial and pharyngeal muscles, though may be generalized convulsions as well. Focal seizures may be less frequently reported than more obvious generalized seizures.	Between seizures, patients have a stereotyped EEG pattern that includes di- or triphasic sharp waves over the central-midtemporal (Rolandic) regions	Prognosis is quite good overall with seizures disappearing by adolescence	Anticonvulsants
Juvenile myoclonic epilepsy (JME)	Begins in patients aged 8 to 20 years	Have normal IQ and are otherwise neurologically intact Known to occur more often in young girls Alcohol is a major contributing factor Is thought to be genetic, though that is not to say that juvenile myoclonic epilepsy will show in immediate family members The seizures are morning myoclonic jerks often with generalized tonic-clonic seizures that occur just after waking Often first diagnosed when they have their first generalized tonic-clonic seizure later in life when they experience sleep deprivation (e.g., freshman year in college after staying up late to study for exams)	Generalized spikes with 4-6 Hz spike wave discharges and multiple spike discharges	---------	Valproic acid is the first line treatment, whereas carbamazepine can actually worsen symptoms Must be taught appropriate sleep hygiene to prevent generalized tonic-clonic seizures
Temporal lobe epilepsy	Seizures begin in late childhood and adolescence	Most common epilepsy of adults In most cases, the epileptogenic region is found in the medial temporal structures (e.g., the hippocampus, amygdala, and parahippocampal gyrus) There is an association with febrile seizures in childhood, and some studies have shown herpes simplex virus (HSV) DNA in these regions, suggesting that perhaps this epilepsy has an infectious etiology. Most of these patients have complex partial seizures sometimes preceded by an aura, and some also suffer from secondary generalised tonic-clonic seizures.	---------	---------	If the patient does not respond sufficiently to medical treatment, surgery may be considered.

• Fetal alcohol syndrome

(FAS) is caused by prenatal alcohol exposure and results in central nervous system (CNS) damage. Seizure disorders due to prenatal alcohol exposure are one of several possible criteria for diagnosing FASD; however, any seizure disorder due to postnatal insult does not qualify as a diagnostic criterion for FASD.

• Frontal lobe epilepsy
• Lennox-Gastaut syndrome
• Occipital lobe epilepsy