IM20.1-5 | Seizure Disorders — Glossary

A neurosurgical procedure involving resection of the anterior temporal lobe, including the amygdala and hippocampus, for drug-resistant mesial temporal lobe epilepsy with hippocampal sclerosis; the most effective surgical treatment for epilepsy, achieving seizure freedom in 60–70% of well-selected patients.

A subjective warning preceding a seizure, representing the ictal phase of a focal seizure before it spreads or generalises; its character localises the seizure onset zone (epigastric rising = mesial temporal; tingling = sensorimotor cortex; flashing lights = occipital).

A group of inflammatory brain disorders caused by antibodies against neuronal surface antigens (anti-NMDAR, anti-LGI1, anti-CASPR2, anti-GABA-B); presents with subacute onset of seizures, psychiatric symptoms, cognitive decline, and movement disorders; treated with immunosuppression.

A fast-acting benzodiazepine administered via the buccal mucosa (10 mg in adults); the preferred route when IV access is unavailable in prehospital status epilepticus; at least as effective as IV lorazepam in RCTs for prehospital SE.

Pre-prescribed emergency seizure medication given by a trained family member or carer at the onset of a prolonged seizure to prevent status epilepticus; options include buccal midazolam (preferred) and rectal diazepam; indicated for patients with known refractory epilepsy or seizures typically lasting >3–5 minutes.

A sodium channel-blocking AED; first-line for focal epilepsy and secondarily generalised tonic-clonic seizures; contraindicated in generalised epilepsies with absence or myoclonic components (worsens these); potent hepatic enzyme inducer (CYP3A4/CYP2C9), causing multiple drug interactions including OCP failure.

A generalised epilepsy syndrome of childhood onset (4–10 years) characterised by frequent brief typical absence seizures; pathognomonic EEG: 3 Hz generalised spike-and-wave provoked by hyperventilation; first-line treatment: ethosuximide or sodium valproate; carbamazepine contraindicated.

A subtype of seizure characterised by involuntary, rhythmic muscle contractions; a motor symptom, not a diagnostic entity; not all seizures are convulsive and not all convulsions are epileptic.

Epilepsy that fails to achieve sustained seizure freedom despite adequate trials of two appropriately chosen and tolerated AEDs (whether as monotherapy or in combination); the threshold for referral to a tertiary epilepsy centre for surgical evaluation.

Recording of the summed electrical activity of cortical pyramidal neurons via scalp electrodes; the most important specific investigation in epilepsy for classification and syndrome identification; a normal interictal EEG does not exclude epilepsy (approximately 50% false-negative rate on a single routine recording).

AEDs that upregulate hepatic CYP enzymes (CYP3A4, CYP2C9), accelerating the metabolism of co-administered drugs; principal EI-AEDs: carbamazepine, phenytoin, phenobarbital, oxcarbazepine (partial); cause OCP failure and reduce warfarin anticoagulation.

A brain disease defined by the ILAE 2014 operational criteria as: ≥2 unprovoked seizures >24 hours apart; OR one unprovoked seizure with ≥60% recurrence probability over 10 years; OR diagnosis of an epilepsy syndrome. Implies a lasting predisposition to generate seizures.

An AED that selectively blocks T-type (low-voltage-activated) calcium channels in thalamo-cortical neurons; first-line for pure typical absence seizures; ineffective against tonic-clonic or focal seizures; not used when GTCS coexist with absence.

A seizure that begins in a network limited to one hemisphere; classified as focal retained awareness (previously simple partial) or focal impaired awareness (previously complex partial); may evolve into focal to bilateral tonic-clonic seizure.

A seizure that engages bilateral distributed cortical networks from onset; subtypes include tonic-clonic, absence, myoclonic, tonic, clonic, and atonic.

Atrophy and gliosis of the hippocampus, most often associated with prolonged febrile seizures in childhood; the most common structural cause of refractory temporal lobe epilepsy; identified on coronal MRI epilepsy protocol; the most surgically remediable form of epilepsy.

A generalised epilepsy syndrome of adolescent onset characterised by morning myoclonic jerks, generalised tonic-clonic seizures (often triggered by sleep deprivation and alcohol), and occasional absence seizures; EEG shows polyspike-and-wave at 3.5–6 Hz; usually requires lifelong AED therapy; carbamazepine and phenytoin are contraindicated.

A sodium channel-blocking AED effective for focal and generalised seizures including absence; requires slow titration (risk of Stevens-Johnson syndrome if escalated rapidly, especially with valproate co-prescription); preferred in women of childbearing age for its comparatively low teratogenicity; levels fall in pregnancy requiring dose escalation.

An AED with a unique mechanism (SV2A synaptic vesicle protein modulation); first-line or alternative for focal and generalised epilepsies; no hepatic CYP metabolism, no significant drug interactions; preferred in liver disease, the elderly, and women of childbearing age; available IV for status epilepticus (60 mg/kg, max 4500 mg).

A benzodiazepine and the preferred first-line IV agent for status epilepticus in adults; dose 0.1 mg/kg IV (max 4 mg) given over 2 minutes; preferred over diazepam because its slower redistribution from brain reduces seizure recurrence.

Atrophy and gliosis of the hippocampus and amygdala, most commonly caused by prolonged febrile seizures in childhood; the substrate of temporal lobe epilepsy; the most surgically remediable epilepsy — anterior temporal lobectomy achieves seizure freedom in 60–70% of selected patients.

Infection of the central nervous system by the larval stage (cysticercus) of Taenia solium (pork tapeworm); the most common identified structural cause of new-onset epilepsy in adults in India; presents with seizures, headache, and focal deficits; diagnosed by CT/MRI showing calcified granuloma or ring-enhancing lesion plus serology.

The electrophysiological hallmark of the epileptic neuron: a large, sustained membrane depolarisation driven by persistent Na⁺ and Ca²⁺ influx, during which the neuron fires at high frequency, followed by prolonged afterhyperpolarisation.

A sodium channel-blocking AED with zero-order (saturable) kinetics at clinical concentrations — small dose increases cause disproportionately large rises in plasma level; toxicity signs: nystagmus (earliest), ataxia, dysarthria, encephalopathy; contraindicated in absence and myoclonic epilepsy; IV form available for SE but associated with cardiac toxicity (QT prolongation, arrhythmia at rapid infusion rates).

A transient rise in serum prolactin (>2× upper limit of normal) occurring within 10–20 minutes of a generalised tonic-clonic or complex focal seizure; normalises by 60 minutes; can help distinguish epileptic seizures from PNES but is not a definitive test (sensitivity approximately 60%).

A structured programme required by regulatory authorities (NICE 2022, MHRA) before prescribing sodium valproate to girls and women of childbearing potential; involves documented counselling on teratogenicity risks, confirmed understanding, use of effective contraception, and annual review.

A seizure occurring as a direct, time-limited response to a known and reversible cause (e.g., hypoglycaemia, hyponatraemia, alcohol withdrawal, acute meningitis); does not define epilepsy; treatment is of the underlying cause, not long-term AED therapy.

Paroxysmal events resembling seizures that have no ictal EEG correlate; a conversion or dissociative disorder; characterised by waxing-waning course, pelvic thrusting, bilateral asynchronous movements, eye closure, absence of cyanosis, and intact corneal reflex during event; diagnosed by video-EEG.

Status epilepticus that persists despite adequate dosing of a benzodiazepine and a second-line IV AED; requires ICU admission, intubation, EEG monitoring, and anaesthetic drug infusion (propofol, midazolam, or thiopental).

A transient occurrence of signs or symptoms due to abnormal, excessive, or synchronous neuronal activity in the brain; the broadest category, encompassing both convulsive and non-convulsive events, provoked and unprovoked.

A broad-spectrum AED effective for all generalised seizure types and focal epilepsy; mechanism includes sodium channel blockade, GABA enhancement, and T-Ca channel blockade; carries the highest teratogenicity risk of commonly used AEDs (neural tube defects, autism spectrum disorder, cognitive impairment in exposed children); requires a Pregnancy Prevention Programme in all girls and women of childbearing potential.

A characteristic EEG pattern comprising a high-amplitude sharp spike followed by a slower wave; generalised 3 Hz spike-and-wave is pathognomonic of typical absence epilepsy; focal spikes indicate a focal cortical irritative zone.

A seizure lasting ≥5 minutes or ≥2 seizures without recovery of consciousness between them; constitutes a neurological emergency due to progressive neuronal injury and GABA-A receptor internalisation that reduces benzodiazepine efficacy over time; stepwise management covered in the companion module.

A seizure lasting ≥5 minutes, or two or more seizures without full recovery of consciousness between them; constitutes a neurological emergency requiring immediate pharmacological treatment; convulsive SE carries 10–20% mortality.

A life-threatening mucocutaneous drug reaction characterised by epidermal detachment, erosive mucositis, and systemic toxicity; a rare but serious risk with lamotrigine, particularly when dose escalation is too rapid or when combined with valproate (which doubles lamotrigine plasma levels); requires immediate drug cessation.

A transient, focal neurological deficit (most commonly weakness) lasting minutes to hours following a focal motor seizure; reflects post-ictal cortical depression at the motor cortex ipsilateral to the affected limb; indicates a focal cortical lesion contralateral to the weakness.

Transient focal neurological weakness, most commonly hemiparesis, following a focal motor seizure; typically lasts minutes to hours; its presence indicates a focal cortical lesion in the contralateral motor cortex and mandates urgent neuroimaging if not already performed.

A seizure with no identifiable acute precipitant at the time of the event; the basis for the diagnosis of epilepsy when recurrent.

A neuromodulation therapy for drug-resistant epilepsy involving an implanted device that delivers intermittent electrical stimulation to the left vagus nerve; reduces seizure frequency by approximately 50% in ~50% of patients; palliative, not curative; an alternative when resective surgery is not feasible.

A pharmacokinetic pattern in which the elimination pathway becomes saturated at clinical drug concentrations, so the rate of elimination is constant (not proportional to concentration); characteristic of phenytoin above ~10 mg/L — small dose increases lead to disproportionately large plasma level rises and unpredictable toxicity.