Erfan Bashar
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Epilepsy — Classification

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Educational scope notice: This is a study note for medical students, not medical advice, diagnosis, or treatment guidance. Clinical management should follow local protocols and current guidelines.

Seizure classification answers one practical question: what network is firing, and how widely. The answer drives drug choice and prognosis. The framework taught here is the International League Against Epilepsy (ILAE) 2017 operational classification, used as the exam-stable vocabulary: it classifies seizures by onset (focal, generalized, or unknown), by awareness (aware versus impaired awareness, for focal seizures), and by motor versus non-motor features. A 2025 ILAE seizure-classification update exists and is not taught here. Older terms such as simple partial and complex partial map onto focal aware and focal impaired awareness; both vocabularies still appear in wards and exam questions.

Focal seizures

Focal seizures arise from networks limited to one hemisphere. They are the most common type, roughly 60% of seizures. A focal aware seizure does not impair consciousness. The person stays alert but may show clonic jerking in one region, a sensory march such as tingling spreading across a limb, autonomic symptoms such as rising epigastric discomfort, or visual and auditory phenomena. Because the discharge stays restricted, the symptom maps the firing cortex.

A focal impaired awareness seizure impairs consciousness, often with a vague, confused, disengaged appearance. These arise most often in the temporal lobe. Typical features include deja vu, a rising epigastric sensation, fear or dreaminess, automatisms such as lip-smacking or chewing, and language disturbance when the dominant hemisphere is involved. An aura is the subjective beginning of such a seizure: a private sensation, felt by the patient and invisible to observers, that localises the onset zone. A focal seizure can spread to both hemispheres, becoming a focal to bilateral tonic-clonic seizure (formerly called secondarily generalized).

Generalized seizures

Generalized seizures rapidly engage bilaterally distributed networks from onset and account for roughly a third of seizures. In a generalized tonic-clonic seizure, consciousness is lost suddenly and the patient falls. The tonic phase holds agonist and antagonist muscles rigid for some 20 to 30 seconds: air forced through constricted airways produces a cry, and incontinence may follow. The clonic phase brings rhythmic jerking as fatiguing neurons alternate contraction with relaxation. The whole episode usually lasts 1 to 2 minutes, and respiratory arrest during the tonic phase makes hypoxia the central concern.

An absence seizure is mostly a childhood event, roughly 5% of seizures. It is a sudden brief pause of awareness lasting around 15 seconds: unresponsive staring, sometimes with eyelid fluttering, and normal behaviour between episodes. Its characteristic EEG signature is a rhythmic spike-and-wave pattern at about 3 Hz. Other generalized types include myoclonic (brief shock-like jerks), tonic (stiffening without clonus), clonic (jerking without a tonic phase), and atonic (sudden tone loss with drop attacks). Epileptic spasms, the flexor or extensor contractions seen mainly in infants, sit under unknown onset.

Etiology

The ILAE framework groups causes into six categories. The groups are not hierarchical: one epilepsy can sit in more than one of them, and the label used depends on the clinical question. Genetic epilepsies come from known or presumed mutations, usually ion channel genes. Most show multifactorial inheritance with age-dependent expression, and only a minority follow Mendelian inheritance. Structural causes are visible CNS lesions: perinatal injury, cortical malformations, hippocampal sclerosis, tumours, trauma, and cerebrovascular disease. A subtle structural lesion needs epilepsy-protocol MRI. Metabolic causes disturb brain biochemistry and lower the threshold. Immune causes involve autoantibodies against neuronal antigens. Infectious causes include meningitis and encephalitis. Unknown means no cause found despite investigation. Older notes saying symptomatic mean structural, and cryptogenic means unknown; these mappings are vocabulary notes, not current claims.

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