CHAPTER 3
The Spectrum of Seizures and Epilepsies

Umair J. Chaudhary and Beate Diehl

EVOLUTION OF SEIZURE AND EPILEPSY CLASSIFICATION

Seizures are heterogeneous clinical phenomena, requiring a standardised classification system to help understand their pathophysiology, determine aetiology, guide management decisions, and facilitate communication between clinicians and researchers.

In the 1960s, Gastaut proposed the first modern classification. This categorised seizures into four groups: partial, generalised, unilateral, and unclassified, based on clinical features, EEG patterns, anatomical substrates, aetiology, and age of onset.¹ The International League against Epilepsy (ILAE) introduced a revised scheme in 1981 that discarded the anatomical substrate and aetiology. It introduced the distinction between ‘simple’ and ‘complex partial’ seizures based on whether or not there is retention or loss of consciousness.² The ability to integrate and respond to stimuli was then defined as consciousness.³

In the following years, several revisions were made, introducing the terms ‘idiopathic’, ‘symptomatic’, and ‘localisation‐related’. A ‘special syndromes’ category was proposed for epilepsies not fitting into other groups.^4,5 This worked well in tertiary centres, but its usability outside such centres was inconsistent, necessitating a reappraisal.^6,7

In 2006, ILAE proposed classifying seizures based on their pathophysiology, anatomical substrates, ictal onset and propagation, and associated syndromes. Seizure types, age of onset, progressive nature, interictal EEG, clinical features, pathophysiology, and genetic basis were used to classify syndromes.⁸ The syndromic classification was seen as essential because epilepsy is a symptom complex reflecting variable aetiologies and diverse clinical, electrophysiological, imaging, and pathological patterns. A novel concept of system epilepsies, involving one or more functionally defined brain systems, categorised epilepsies into four types based on aetiology, discarding idiopathic and symptomatic epilepsies.^9,10 This idea was not widely accepted,¹¹ leading to new classifications in 2010¹² and 2017.¹³

Key changes in the 2010 classification¹² conceptualised generalised seizures as originating in bilaterally distributed networks, modified the subclassification of absence seizures, and recognised myoclonic absence seizures and eyelid myoclonia. Simple and complex partial seizures were merged into focal seizures. Secondarily generalised seizures were renamed bilateral convulsive seizures.

Neonatal seizures and infantile spasms were incorporated into the classification. ‘Genetic’, ‘structural/metabolic’, and ‘unknown’ replaced terms such as idiopathic, symptomatic, and cryptogenic as causes and ‘self‐limiting’ replaced ‘benign’. The 2010 ILAE classification incorporated advancements in genetic understanding, offered flexibility to describe syndromes across multiple axes.^14,15,16. It also facilitated the identification of lateralising and localising features through descriptive terminology and enabled better prognostic insights, particularly for epilepsy surgery.^17,18

Seizure classification schemes became more clinically relevant. The focus initially was on broad categories such as focal or generalised; however, it was acknowledged that seizure semiology was important. In 1998, Lüders proposed a system centred on ictal semiology, describing the main clinical features of a seizure,¹⁹ which has been widely accepted and refined in epilepsy surgery centres. It allowed for a description of symptom evolution, enabling a link to specific body parts. For example, a seizure might be classified from the initial tingling sensation in the left hand, evolving to a contraction in that same limb, as a left‐hand sensory aura followed by a left‐hand/arm tonic seizure. This approach helps in understanding seizure origin, as an aura refers to a subjective feeling only and may not be associated with an EEG change. In contrast, seizures are outwardly visible or measurable signs. Such detailed information is invaluable for determining seizure location and whether surgery could be an option. Recently, a four‐dimensional individual‐centred classification integrating ictal semiology, the epileptogenic zone, aetiology, and comorbidities has been proposed.²⁰ This helped describe the clinical evolution of seizures, but information on frequency, precipitating factors, and postictal behaviours was lacking. With advances in neuroimaging, providing insights into ictal anatomy, a five‐axis diagnostic scheme was proposed in 2001, aiming to improve understanding of seizure types, syndromes, causes, and prognosis.²¹

ILAE SEIZURE CLASSIFICATION 2017

The 2017 ILAE seizure classification was based on electro‐anatomical phenomenology, dividing seizures into two categories: those with a ‘focal onset’ and those with a ‘generalised onset’. A third option was introduced: ‘unknown onset’, as it is not always possible to determine at the time of the classification, or if inadequate data are available.

Focal seizures were defined as ‘originating within networks limited to one hemisphere. They may be discreetly localised or more widely distributed. Generalised seizures from the onset were described as ‘originating at some point within, and rapidly engaging, bilaterally distributed networks’. Seizure semiology served as the basis for categorising seizures. Further characterisations included whether awareness is retained or impaired. Generalised motor seizure characteristics comprised nine sub‐categories: atonic, clonic, epileptic spasms, myoclonic, myoclonic–atonic, myoclonic–tonic–clonic, tonic, or tonic–clonic. Generalised nonmotor seizures included typical absence and atypical absence seizures.

This classification combined semiological data with information from other sources. The intended use of the terminology did not include the evolution of symptoms within the episode. For example, if there is loss of awareness at any time, the seizure is classified as an impaired awareness, potentially losing information to understand where such a seizure may originate

ILAE EPILEPSY CLASSIFICATION 2017 AND 2022

The 2017 ILAE classification of the epilepsies introduced a structured and flexible framework.²² This maintains a three‐level diagnostic structure: seizure type, epilepsy type, and syndrome, while incorporating new terminology that reflected advances in genetics, neuroimaging, and clinical knowledge. Epilepsies were categorised as generalised, focal, combined generalised and focal, or unknown. Generalised epilepsies included seizures originating from bilateral networks and typically associated with generalised spike–wave EEG patterns. Focal epilepsies included seizures originating in one hemisphere, often linked to structural lesions on imaging. The combined category was added to account for syndromes, such as Dravet syndrome (DS), in which both seizure types coexist. Unknown epilepsies included those in which the seizure origin was uncertain.

This classification replaced idiopathic, symptomatic, and cryptogenic aetiologies with structural, genetic, infectious, metabolic, immune, and unknown aetiologies. Genetic epilepsies included epilepsies with pathogenic mutations, such as DS and many generalised epilepsies. Structural/metabolic epilepsies had identifiable causes, including cortical dysplasia and mesial temporal sclerosis. The term ‘unknown’ was used for cases in which the underlying cause was uncertain or unidentified. Aetiology needed to be determined independently of epilepsy/syndrome type. Electroclinical syndromes were defined based on age of onset, seizure types, EEG patterns, and clinical features, e.g. Lennox–Gastaut syndrome (LGS), West syndrome, and juvenile myoclonic epilepsy. The developmental and epileptic encephalopathies (DEE) included conditions in which epileptic activity contributes to developmental and cognitive regression, e.g. DS and Ohtahara syndrome. The term ‘self‐limited’ replaced ‘benign’ to circumvent misconceptions that these do not require treatment or monitoring, e.g. childhood absence epilepsy and benign epilepsy with centrotemporal spikes, which typically resolve in adolescence. The 2017 classification emphasised the significance of cognitive, behavioural, and psychiatric comorbidities, which may impact upon quality of life and require directed management.

The 2022 update improved syndrome definitions, emphasising age‐specific, electroclinical, and genetic features. The ILAE 2022 generalised epilepsies’ classification include the concept of genetic generalised epilepsy, and acknowledged overlaps with focal epilepsies and among generalised subtypes.^23–26

ILAE SEIZURE CLASSIFICATION 2025

The ILAE 2025 Seizure classification.²⁷ refines the categories based on clinical experience, feedback from stakeholders and evolving evidence, providing a flexible framework to incorporate seizure descriptors. It maintains the 2017 structure, retaining the four categories: focal, generalised, unknown, and unclassified. ‘Onset’ is excluded, and ‘consciousness’ replaces ‘awareness’, providing a more accurate account of cognition during a seizure. Consciousness encompasses awareness, responsiveness, and the ability to interact with the environment, whereas awareness focuses mainly on the perception of the external environment. Classifiers are features directly impacting clinical management (e.g. seizure type or consciousness), while descriptors provide additional information about seizure characteristics (e.g. semiology, observable vs. non‐observable features). The motor vs. non‐motor dichotomy is replaced by the observable vs. non‐observable distinction to reflect seizure phenomena better. The chronological sequence of seizure semiology is used to describe seizures, rather than relying on the first sign.

Basic and extended versions of the classification are available (Table 3.1). Focal seizures are divided into focal preserved consciousness seizure (FPC) and focal impaired consciousness seizure (FIC), using consciousness as a classifier. The term FPC replaces ‘focal aware seizure, simple partial seizure’ and ‘aura‘. If impaired consciousness occurs during seizure progression, the episode will be classified as a FIC, replacing the term ‘complex‐partial seizure / focal dyscognitive/unaware/impaired consciousness seizure’. Further characterisation is based on key seizure signs and symptoms (semiology), whether they are observable or non‐observable, and is described in chronological order, specifying which body part/side is affected. Observable signs and symptoms include elementary/complex motor, autonomic and cognitive/language phenomena (Table 3.1). Non‐observable phenomena include sensory symptoms (Table 3.1). Seizures may start with focal preserved consciousness symptomatology, evolving into loss of consciousness, or directly start with loss of consciousness. Seizures can have a focal beginning (the aura), which can evolve and spread to become a bilateral tonic–clonic seizure, progressing from focal to bilateral tonic–clonic (FBTCS).

Seizures of unknown onset, i.e. uncertain whether focal or generalised, may still be classified if consciousness is preserved or impaired and if there are observable or non‐observable manifestations.

Generalised seizures arise from large or focal areas of the cortex or networks and rapidly engage wider networks involving both hemispheres. Generalised absence seizures include typical absence, atypical absence, myoclonic absence, and eyelid myoclonia with/without absence seizure. Generalised tonic–clonic (GTC) seizures may have myoclonic or absence seizures before GTC. Other generalised seizures include generalised myoclonic, generalised clonic, generalised negative myoclonic, generalised epileptic spasms, generalised tonic, generalised atonic, and generalised myoclonic–atonic seizures.

Table 3.2 compares the evolving terminology for seizures and epilepsy types over the years.

Table 3.1 2025 ILAE classification of seizure type.

Source: Adapted from ILAE Updated seizure classification 2025.²⁷

		Descriptor
Classifier
Focal	Preserved consciousness	Non‐observable manifestation	Somatotopic modifier (left, right, bilateral–symmetric, bilateral–asymmetric) + body part) Semiology feature (describe in chronological sequence) Non‐observable manifestation Auditory, Body‐perception illusion, Depersonalization, Gustatory, Olfactory, Somatosensory, Painful, Nonpainful, Vestibular/dizziness, Visual Observable manifestations Elementary motor phenomenon Akinetic, Astatic, Atonic, Clonic, Dystonic, Epileptic nystagmus, Epileptic spasm, Eye blinking/deviation, Gyratory, Head orientation, Ictal paresis, Myoclonic, Myoclonic–atonic, Epileptic negative myoclonus, Tonic (focal tonic, chapeau de gendarme, fencing posture), tonic–clonic (figure‐of‐four), Versive Complex motor phenomenon Automatisms: proximal/distal/genital, Ictal grasping, gelastic, dacrystic, oroalimentary, verbal, vocal Hyperkinetic behaviour Possible observable manifestation Cognitive/language: Aphasia, Confusion / disorientation, Dysmnesia (Amnesia, Déjà vu, déjà vécu, jamais vu, dreamy state, reminiscence). Forced thinking, anosognosia, apraxia, neglect Autonomic: Ictal asystole/bradycardia/tachycardia, Flushing, Piloerection, Sweating, Borborygmi, Flatulence, Hypersalivation, Nausea/vomiting, Polydipsia, Sialorrhea, Spitting, Miosis, Mydriasis, Apnoea, Choking, Hyperventilation, hypoventilation, Urinary incontinence/urge Affective (Emotional): Anger, Anxiety, Ecstatic/bliss, Fear, Guilt, Mirth, Mystic, Sadness, Sexual
	Preserved consciousness	observable manifestation
	Impaired consciousness	Non‐observable manifestation
	Impaired consciousness	observable manifestation
	Bilateral tonic clonic	Bilateral tonic clonic
Unknown whether focal or generalised	Preserved consciousness	Non‐observable manifestation
	Preserved consciousness	observable manifestation
	Impaired consciousness	Non‐observable manifestation
	Impaired consciousness	observable manifestation
	Bilateral tonic clonic	Bilateral tonic clonic
Classifier
Generalised	Absence	Typical absence
		Atypical absence
		Myoclonic absence seizure
		Eyelid myoclonia with/without absence
	Tonic–clonic	Myoclonic tonic–clonic seizure
	Tonic–clonic	Absence‐to‐tonic–clonic seizure
	Generalised myoclonic
	Generalised clonic seizure
	Generalised negative myoclonic seizure
	Generalised epileptic spasms
	Generalised tonic seizure
	Generalised atonic seizure
	Generalised myoclonic–atonic seizure
Unclassified

Table 3.2 Comparative terminology for similar seizure/epilepsy types.^2,10,22,27

1981	2010	2017	2025
ILAE Seizure Classification
Simple Partial	Focal seizure without dyscognition	Focal Aware Seizure	Focal Preserved Consciousness Seizure
Complex Partial	Focal seizure with dyscognition	Focal Impaired Awareness Seizure	Focal Impaired Consciousness Seizure
Secondarily Generalized	Focal seizure with secondary generalisation	Focal to Bilateral Tonic–Clonic Seizure	Focal to Bilateral Tonic–Clonic Seizure
Absence	Typical/atypical absence	Generalised Non‐Motor Absence (Typical/Atypical)	Generalised Absence (Typical/Atypical)
Tonic–Clonic (Generalised)	Generalised tonic–clonic	Generalised Motor Seizure – Tonic–Clonic	Generalised Tonic–Clonic Seizure
Not included	Epileptic spasms	Epileptic Spasms	Epileptic Spasms
Not defined	Not classified	Not explicitly classified	Negative Myoclonus
ILAE Epilepsy Classification
1989	2010	2017/2022
Localisation‐Related Epilepsy	Focal Epilepsy	Focal Epilepsy
Generalised Epilepsy	Generalised Epilepsy	Generalised Epilepsy
Idiopathic	Genetic Generalised Epilepsy	Genetic Generalised Epilepsy
Symptomatic	Structural/Metabolic Epilepsy	Structural/Metabolic Epilepsy
Cryptogenic	Unknown Epilepsy	Unknown Epilepsy
Emphasised (e.g. Lennox–Gastaut, West syndrome)	Electroclinical syndromes	Epilepsy syndromes

FOCAL SEIZURES AND EPILEPSY

These may occur as FPC seizure (auras) without or with evolution to loss of consciousness or as an FIC seizure. Focal seizures can arise from any cortical region, the most common being the frontal and temporal lobes. Assessment of seizure semiology is crucial and greatly assists in formulating an initial hypothesis of potential anatomic areas from which seizures originate, which is relevant in determining therapeutic options.

FOCAL PRESERVED CONSCIOUSNESS SEIZURES (AURAS)

Symptomatology depends on anatomical localisation of seizures, with specific features linked to cortical regions (Tables 3.1 and 3.3). Observable features at onset in full consciousness, including elementary motor phenomena such as myoclonic, epileptic spasms, or posturing, may suggest activation of the primary motor cortex and the pericentral region. If large body areas are involved, the ictal discharge usually activates premotor areas, and loss of consciousness may occur. If a seizure remains confined to the supplementary motor area, bilateral body postures (e.g. figure of four, fencing posture) may occur without loss of consciousness. Head or eye version, particularly at seizure onset with retained consciousness, indicates involvement of the frontal eye field and surrounding areas and is a reliable contralateral lateralising sign. Speech arrest or dysarthria may arise from language or supplementary motor areas, while aphasia suggests involvement of primary language areas. Todd’s paralysis can occur after a seizure, indicating contralateral seizure onset. Automatisms in FPC seizures suggest a localisation in the non‐dominant temporal lobe.

Table 3.3 Focal seizures arising in different brain regions.

Source: Adapted from Beniczky et al.²⁷

Brain region of origin	Clinical features
Mesial temporal lobe	Often, evolution from aura to loss of awareness, with automatisms of mouth and hands
	Auras are common and include visceral, cephalic, gustatory, cognitive, affective, perceptual, or autonomic auras
	Slow evolution of seizure
	Dystonic posturing of the contralateral upper limb common in the early stages of the seizure
	In seizures arising in the dominant temporal lobe, postictal aphasia is common
	Seizures more prolonged than frontal lobe seizures (typically >2 min), with a slower evolution and more gradual onset/offset
	Postictal confusion common
	Autonomic changes (e.g. pallor, redness, and tachycardia)
	Automatisms: less violent than in frontal lobe epilepsy, and usually take the form of oro‐alimentary (lip‐smacking, chewing, swallowing), or gestural (e.g. fumbling, fidgeting, repetitive motor actions, undressing, walking, sexually directed actions, walking, running) and sometimes prolonged
	Common aetiology: hippocampal sclerosis, often associated with a history of febrile seizures, onset in childhood or adolescence, initial early treatment response lost after several years
Lateral temporal lobe	Features overlap with mesial temporal lobe onset, with the following differences:
	Aura is more likely to take the form of complex perceptual changes, visual and auditory hallucinations
	Tonic posturing is more common
	More frequent secondary generalisation
Frontal lobe	Frequent attacks with clustering
	Brief stereotyped seizures (<30 s)
	Nocturnal attacks common
	Sudden onset and cessation, with rapid evolution
	Complex auras uncommon
	Version of head or eye common
	Prominent ictal posturing and tonic spasms
	Prominent complex bilateral motor automatisms involving lower limbs; often bizarre and misdiagnosed as dissociative seizures
	Postictal confusion uncommon
	History of status epilepticus
Parietal and occipital lobe	Somatosensory symptoms (e.g. tingling, numbness, or more complex sensations – may or may not march) Sensation of inability to move
	Sexual sensations
	Illusions of change in body size/shape
	Vertigo
	Gustatory seizures
	Elementary visual hallucinations (e.g. flashes, colours, shapes, patterns)
	Complex visual hallucinations (e.g. objects, scenes, autoscopic, palinopsia, often moving)
	Head‐turning (usually adversive, with a sensation of following the visual hallucination)
	Visuospatial distortions (e.g. of size [micropsia, macropsia], shape, position)
	Loss or dulling of vision (amaurosis)
	Eyelid fluttering/blinking/nystagmus
Central cortex	Often no loss of consciousness
	Contralateral jerking (which may or may not march)
	Contralateral tonic spasm or dystonia
	Posturing, which is often bilateral
	Speech arrest and spasm of bulbar musculature (producing anarthria or a choking, gurgling sound)
	Contralateral sensory symptoms
	Short duration and frequently recurring attacks
	Prolonged seizures with slow progression (and episodes of epilepsia partialis continua)
	Postictal Todd’s paresis

Non‐observable manifestations may include somatosensory symptoms such as tingling, numbness, or painful sensations from primary sensory cortex, insula; visual auras (e.g. flashing lights, colours, blindness) from calcarine cortex; auditory, gustatory, olfactory from temporal, insular, or orbitofrontal regions; vestibular/dizziness, body‐perception illusions, or depersonalisation from parietal, temporoparietooccipital junction. A rising epigastric sensation is the most common manifestation of an FPC in the mesial temporal lobe. These features may not be visible to observers, but some can be assessed during a seizure, such as by checking visual fields or assessing sensation.

Possible observable features include autonomic manifestations measurable by ECG monitoring, such as ictal bradycardia, tachycardia, asystole; pupil changes (such as miosis or mydriasis) detected by pupillometry; and respiratory alterations (like apnoea, hyperventilation, or hypoventilation) monitored via capnography or respiratory monitoring. Other autonomic signs may also occur and vary in detectability, including flushing, piloerection, sweating, borborygmi, flatulence, nausea, vomiting, hypersalivation, sialorrhea, spitting, polydipsia, and urinary urge or incontinence. Autonomic manifestations can be early ictal, ictal, or postictal, pointing towards the involvement of the limbic network.

Complex perceptual or affective ‘auras’/FPC seizure can take various forms and occur in seizures arising from temporal, frontal, or parietal regions. There are six principal categories:

Dysphasic symptoms occur when cortical speech areas (frontal or temporoparietal) are affected and should be distinguished from anarthria, which suggests fronto‐central involvement.
Dysmnestic symptoms such as flashbacks, déjà vu, jamais vu, or memory distortions are most common in mesial temporal lobe seizures, and also occur in the inferior frontal or lateral temporal lobe seizures.
Cognitive symptoms include dreamy states and sensations of unreality or depersonalisation, and occur primarily in seizures involving the temporal lobe and limbic system.
Affective symptoms include fear, depression, anger, elation, erotic thoughts, serenity, or exhilaration. These are encountered most in mesial temporal lobe epilepsy (TLE). Mirthless laughter is a feature of automatism (gelastic seizures) arising in frontal areas, consistently associated with hypothalamic hamartomas.
Illusions of size (macropsia, micropsia), shape, weight, distance, or sound usually indicate temporal or parieto‐occipital epileptic foci.
Structured hallucinations of visual, auditory, gustatory, or olfactory forms, which can be crude or elaborate, usually arise in the temporal or parieto‐occipital association areas. Visual hallucinations vary in sophistication, ranging from simple colours or flashing lights, which can arise in the calcarine cortex in epilepsy, to complex visual perceptual hallucinations in posterior temporal association areas. Auditory hallucinations and changes in auditory perception vary in complexity and commonly occur in seizures arising in Heschl’s gyrus. Gustatory hallucinations are a frequent symptom of TLE.

FOCAL IMPAIRED CONSCIOUSNESS SEIZURES

Sixty per cent of FIC seizures arise from the temporal lobes, 30% from the frontal, and 10% from the posterior areas. A FIC seizure may evolve during its course. In some cases, it is possible to identify three distinct components: the aura, loss of consciousness, and automatisms or other associated phenomena. The aura is usually short‐lived, lasting a few seconds, but may be prolonged. The aura can take any form, depending on the location of the epileptic discharge. When loss of consciousness occurs, there is often motor and speech arrest, during which the individual appears vacant.

Automatisms are involuntary motor actions during or in the aftermath of seizures in a state of impaired consciousness. The individual is usually amnesic for the automatism. Sometimes automatisms have purposeful elements, are affected by the environment, and may include quite complex activities. Automatisms need to be differentiated from postictal confusion. In some instances, seizures arising from the non‐dominant temporal lobe may preserve consciousness, despite automatisms or the formation of brief words and sentences being spoken (ictal speech), typically without any subsequent memory of this event.

Automatisms are most common in temporal and frontal seizures. The most common automatisms are:

Oro‐alimentary automatisms consist of orofacial movements such as chewing, lip‐smacking, swallowing, or drooling.
Gestural automatisms include fiddling with the hands, tapping, patting, rubbing, ordering, and tidying. Complex actions such as undressing are common, particularly in mesial TLE.
Ambulatory automatisms involve walking, circling, and running and are most common in frontal lobe epilepsy but may also occur in TLE.
Verbal automatisms include words and sentences, as well as meaningless sounds, such as humming and whistling. Verbal automatisms can occur in frontal and temporal seizures. Speech during an episode suggests that it arises from the non‐dominant hemisphere, and post‐seizure dysphasia indicates it originates in the dominant hemisphere.
Violent behaviour can occur in an automatism. It is best considered reactive in an acutely confused person and is especially likely if the person is restrained. The violent actions of epileptic automatism are generally not premeditated, never recalled, never highly coordinated or skilful, and seldom goal‐directed. These are helpful diagnostic features in a forensic context.

Focal epilepsy can also be classified by anatomical location into those arising in the frontal, temporal, parietal, and occipital lobes, as well as in the central region (pre‐ and post‐central gyrus) (Table 3.3). Seizures arising from subdivisions of the frontal lobe, such as mesial, orbitofrontal, and lateral frontal, as well as pericentral regions, have semiological differences that are helpful for seizure localisation. Most focal epilepsies, however, arise in the temporal lobe. In general, the more complex ictal behaviours indicate the involvement of a widespread network of cortical and subcortical regions. Any focal seizure can progress into an FBTC seizure.

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Oct 17, 2026 | Posted by admin in NEUROLOGY | Comments Off

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3: The Spectrum of Seizures and Epilepsies