Seizure Semiology & Localization
Seizure Definitions, Semiology & Localization
What You'll Learn
- ILAE 2025 seizure classification (Beniczky et al., Epilepsia 2025) is a published ILAE position paper that builds on the 2017 framework: “awareness” → consciousness (defined by awareness + responsiveness); “motor/non-motor” → observable/non-observable manifestations; “onset” removed from class names. Know both: 2017 focal aware/impaired awareness and 2025 consciousness/observable-manifestation terminology.
- Focal seizures are classified by consciousness (preserved vs. impaired) and described by chronological semiologic sequence
- 21 seizure types across 4 classes (focal, generalized, unknown, unclassified) — down from 63 in 2017; classifiers (guide management) vs. descriptors (semiological features)
- Three-level framework: seizure type → epilepsy type → epilepsy syndrome; six etiologies (structural, genetic, infectious, metabolic, immune, unknown)
- Mesial temporal sequence: epigastric rising → behavioral arrest → oroalimentary automatisms → contralateral dystonic posturing
- Key lateralizing signs: figure-of-4 extended arm = contralateral; postictal nose wipe = ipsilateral hand; Todd paralysis = contralateral; dystonic posturing (~90% reliable)
- Epilepsy diagnosis: 2 unprovoked seizures >24h apart, OR 1 seizure + ≥60% recurrence risk, OR epilepsy syndrome
HighYield Pearls
- ILAE 2017 framework (board standard): focal-onset (aware vs impaired awareness; motor vs non-motor) — generalized-onset (motor — tonic-clonic, clonic, tonic, myoclonic, MAS, atonic, epileptic spasms; non-motor — typical/atypical/myoclonic absence, eyelid myoclonia) — unknown-onset — unclassified. ILAE 2025 (consciousness, observable/non-observable) is the current ILAE classification; the 2017 framework remains common exam/legacy terminology.
- Mesial temporal (most common focal epilepsy): epigastric rising aura → déjà vu/fear → behavioral arrest → oroalimentary automatisms (lip-smacking/chewing) + ipsilateral hand automatisms + contralateral dystonic posturing → prolonged postictal confusion → ipsilateral nose wipe. MRI: hippocampal sclerosis.
- Lateral (neocortical) temporal: auditory aura (buzzing, voices, distorted sounds — Heschl gyrus); earlier speech arrest, less prominent automatisms.
- Frontal lobe: bilateral asymmetric tonic posturing / fencer’s posture (SMA), hypermotor “bicycling” / thrashing, nocturnal clusters, brief (<30 sec), rapid postictal recovery, interictal EEG often normal. SMA: preserved awareness despite bilateral motor activity.
- Parietal: somatosensory aura (tingling, Jacksonian march), body image distortion, ictal pain (rare — insular more often). Occipital: elementary visual hallucinations (flashes, colored circles — contrast with formed hallucinations of psychiatric disease / Charles Bonnet), eyelid fluttering, ictal nystagmus, postictal headache and visual deficit. Insular: laryngeal/throat constriction, visceral/painful, dysesthetic paresthesias — suspect after failed temporal surgery.
- Lateralizing signs (high yield): figure-of-4 at GTC onset → extended arm = contralateral to onset; unilateral dystonic posturing → contralateral (~90% reliable); early forced head version (sustained >10 sec pre-GTC) → contralateral; late head turning during GTC → often ipsilateral (FALSE lateralizing); Todd paralysis → contralateral; postictal nose wipe (hand) → ipsilateral hemisphere; postictal aphasia → dominant (usually left); ictal speech preservation → non-dominant; ictal vomiting/spitting → non-dominant (right) temporal.
- Epileptic seizure vs PNES: GTC features — eyes open, synchronous tonic-clonic, lateral tongue bite, urinary incontinence, postictal acidosis, postictal EEG slowing, brief duration, no recall. PNES — forced eye closure, pelvic thrusting, side-to-side head shake, asynchronous flailing, preserved awareness with bilateral motor activity, recall of details, normal post-ictal EEG, no acidosis, prolonged/waxing-waning course.
- Hyperkinetic frontal seizures (stereotyped + nocturnal + brief) are epileptic, NOT PNES — classic board trap. NREM parasomnias are non-epileptic and unrelated.
- Gelastic seizures (ictal laughter) → hypothalamic hamartoma + precocious puberty + cognitive/behavioral decline.
- Status epilepticus (Trinka 2015): GCSE — treat at 5 min (t1), injury at 30 min (t2); focal SE with impaired awareness — t1 10 min, t2 >60 min; absence SE — t1 10–15 min.
🔍 Quick ReferenceSemiology · Localization clues · Postictal / lateralizing
Semiology / aura
- Epigastric rising sensation + déjà vu + fear → mesial temporal (amygdala/hippocampus)
- Auditory aura (buzzing, voices, distorted sounds) → lateral temporal — Heschl gyrus
- Olfactory “uncinate fits” (burning/chemical smell) → uncus / mesial temporal (also orbitofrontal)
- Laryngeal constriction / throat tightening + visceral / dysesthetic pain → insular cortex
- Elementary visual hallucinations (multicolored flashes, circles in contralateral field) → occipital pole
- Somatosensory tingling with Jacksonian march + body-image distortion → parietal (primary sensory cortex)
- Cephalic / no aura + hypermotor “bicycling” or fencer’s posture, nocturnal → frontal lobe
- Gustatory (metallic/bitter) aura → insula / parietal operculum
- Ictal emesis + pallor (child, nocturnal) → Panayiotopoulos — occipital with autonomic features
Ictal localization signs
- Oroalimentary automatisms (lip-smacking, chewing) + ipsilateral hand automatisms + contralateral dystonic posturing → mesial temporal lobe epilepsy (classic MTLE sequence)
- Bilateral asymmetric tonic / fencer’s posture with preserved awareness, <30 sec, nocturnal → SMA (mesial frontal, area 6)
- Hypermotor “bicycling,” thrashing, rocking — brief, stereotyped, nocturnal clusters → frontal lobe (NOT PNES)
- Forced contralateral eye/head version (sustained >10 sec pre-GTC) → frontal eye fields (Brodmann area 8), contralateral to onset
- Figure-of-4 at GTC onset (one arm extended, one flexed) → extended arm contralateral to onset
- Unilateral clonic activity / Jacksonian march → contralateral primary motor cortex
- Eyelid fluttering + ictal nystagmus + contralateral eye deviation → occipital
- Ictal spitting → nondominant (right) temporal lobe
- Gelastic (ictal laughter, mirthless) → hypothalamic hamartoma (also anterior cingulate)
Postictal / lateralizing
- Postictal nose wiping with one hand → ipsilateral hemisphere (if dystonic posturing present, wipe is done by the non-dystonic — thus contralateral — hand, still ipsilateral to focus)
- Postictal aphasia → dominant hemisphere (usually left)
- Ictal speech preservation during bilateral motor activity → non-dominant hemisphere
- Todd paralysis (postictal focal weakness, resolves min–hours) → contralateral to focus
- Prolonged postictal confusion (30 sec — several min) → temporal lobe; rapid recovery / minimal confusion → frontal lobe
- Postictal headache + transient visual deficit/blindness → occipital
- Postictal psychosis after lucid interval (hours–days) → temporal lobe (often after seizure cluster)
- Lateral tongue bite + urinary incontinence + postictal lactic acidosis + EEG slowing → true GTC (helps distinguish from PNES)
- Forced eye closure + pelvic thrusting + side-to-side head shake + asynchronous flailing + recall preserved + normal post-event EEG → PNES
Seizure Classification (ILAE 2017 — Board Standard; ILAE 2025 supplementary)
Exam Note
ILAE 2017 remains the most familiar board framework (focal aware / focal impaired awareness / focal to bilateral tonic-clonic; motor vs non-motor), but the ILAE 2025 seizure classification is a published ILAE position paper. Know both: 2017 focal aware/impaired awareness and 2025 consciousness / observable-manifestation terminology.
Terminology Evolution
| Old Term | 2017 Term | 2025 Term |
|---|---|---|
| Simple partial seizure | Focal aware seizure | Focal preserved consciousness seizure (FPC) |
| Complex partial seizure | Focal impaired awareness seizure | Focal impaired consciousness seizure (FIC) |
| Secondarily generalized tonic-clonic | Focal to bilateral tonic-clonic | Focal-to-bilateral tonic-clonic seizure (FBTC) |
| Grand mal | Generalized-onset tonic-clonic | Generalized tonic-clonic seizure (GTC) |
| Petit mal | Absence (non-motor) | Absence seizure (“non-motor” removed) |
| Aura | Focal aware seizure | Focal preserved consciousness seizure |
Key Changes: ILAE 2017 → Proposed 2025 Update
| Feature | 2017 | 2025 |
|---|---|---|
| Class naming | “Focal-onset,” “Generalized-onset” | “Focal,” “Generalized” — “onset” removed (generalized seizures can have focal onset) |
| Classifier | Awareness (aware vs. impaired) | Consciousness (preserved vs. impaired) = awareness (recall) + responsiveness (react to verbal/motor tasks) |
| Descriptors | Motor vs. non-motor onset | Observable vs. non-observable manifestations (basic); chronological semiologic sequence (expanded) |
| Seizure description | First sign at onset determines subtype | Chronological sequence of all signs (e.g., aura → automatism → impaired responsiveness) |
| New seizure type | — | Generalized negative myoclonus (brief <500 ms interruption of tone) |
| Epileptic spasms | Seizure type in all classes | Seizure type only in generalized; descriptor in focal and unknown |
| Absence seizures | Classified as “non-motor” | “Non-motor” removed (absences often have observable motor features: automatisms, blinks, retropulsion) |
| Taxonomy | 63 seizure types; classifiers & descriptors not distinguished | 21 seizure types; classifiers (biological classes; guide management) vs. descriptors (semiological features) |
Complete Taxonomy: 4 Classes, 21 Seizure Types
| Class | Seizure Types | Abbreviation |
|---|---|---|
| 1. Focal (F) | Focal preserved consciousness | FPC |
| Focal impaired consciousness | FIC | |
| Focal-to-bilateral tonic-clonic | FBTC | |
| 2. Unknown (U) (whether focal or generalized) | Preserved consciousness | PC |
| Impaired consciousness | IC | |
| Bilateral tonic-clonic | BTC | |
| 3. Generalized (G) | 3.1 Absence seizures: | |
| Typical absence | TA | |
| Atypical absence | AA | |
| Myoclonic absence | MA | |
| Eyelid myoclonia ± absence | EMA | |
| 3.2 Generalized tonic-clonic (GTC): | ||
| Myoclonic-tonic-clonic | — | |
| Absence-to-tonic-clonic | — | |
| 3.3 Other generalized seizures: | ||
| Myoclonic / Clonic / Tonic / Atonic / Myoclonic-atonic | GM, GC, GT, GA, GMA | |
| Negative myoclonic (NEW) | GNM | |
| Generalized epileptic spasms | GES | |
| (Epileptic spasms in focal/unknown = descriptor, not seizure type) | ||
| 4. Unclassified | No meaningful seizure characteristics available | |
Consciousness as a Classifier
- Consciousness replaces “awareness” — operationally defined by:
- Awareness: ability to recall the event afterward
- Responsiveness: ability to respond to verbal and motor tasks during the seizure
- If either is impaired → classify as impaired consciousness
- Applies as classifier only to focal and unknown seizures; most generalized seizures impair consciousness — myoclonic seizures are a notable exception (consciousness usually preserved — patient drops object and remains aware)
- If consciousness undetermined → classify under the parent term (e.g., just “focal seizure”)
- Caution: isolated epileptic amnesia, ictal paresis, or ictal receptive aphasia can mimic impaired consciousness
Observable vs. Non-observable Manifestations
- Basic version (primary care, resource-limited): seizures described as with or without observable manifestations
- Expanded version (specialized centers): semiological features listed in chronological sequence using arrows (e.g., epigastric aura → right hand automatism → impaired responsiveness)
- Observable = motor, aphasic, autonomic, or other features readily identified by eyewitnesses; non-volitional
- Non-observable = sensory, cognitive, affective phenomena; indescribable auras
- Impaired consciousness itself counts as an observable manifestation
- “Non-motor” removed from absence seizure classification because absences often show observable motor features (automatisms, eyelid blinking, head retropulsion)
Generalized Seizure Subtypes
Absence Seizures
- Typical absence: abrupt stare, ≥2.5 Hz (classically 3 Hz) generalized spike-wave; rapid recovery; no postictal confusion; median few seconds to 30 s
- Atypical absence: slower onset/offset, <2.5 Hz slow spike-wave; pronounced tone changes; Lennox-Gastaut
- Myoclonic absence: rhythmic 3 Hz bilateral upper-limb jerks with arm abduction; median 7–12 s
- Eyelid myoclonia: brief 3–6 Hz eyelid jerks ± absence; median 1.5 s; Jeavons syndrome
Generalized Tonic-Clonic & Subtypes
- Generalized tonic-clonic (GTC): sustained tonic phase → progressive slowing clonic phase; median 80 s; bilateral but may be asymmetric
- Myoclonic-tonic-clonic: myoclonic jerks preceding GTC (classic JME)
- Absence-to-tonic-clonic: absence seizure evolving into GTC
Other Generalized Seizures
- Myoclonic: brief (<100 ms) bilateral jerks; JME (morning predominance)
- Clonic: regular, repetitive myoclonic jerks at low frequency; median 4 s; neonates/young children
- Tonic: sustained bilateral muscular contraction; median 8 s; Lennox-Gastaut
- Atonic: sudden loss/decrease in muscle tone; drop attacks; median 1 s; LGS
- Myoclonic-atonic: brief myoclonic jerk followed by atonic component; median 1.25 s; Doose syndrome
- Negative myoclonic (NEW in 2025): brief (<500 ms) interruption of muscle tone; requires voluntary activation to document; distinct from asterixis in toxic-metabolic encephalopathies. Can also be focal (cortical), classically centroparietal, seen in atypical benign partial epilepsy / ESES spectrum
- Generalized epileptic spasms: brief (≤2 s) axial muscle contractions; clusters upon awakening; infantile epileptic spasm syndrome (IESS)
Epileptic Spasms: Updated Classification
- Generalized (bilateral symmetric) = seizure type (“generalized epileptic spasms”)
- Focal (unilateral or asymmetric) = descriptor within focal seizure semiology (“focal epileptic spasm”)
- Unknown = descriptor when focal vs. generalized cannot be determined
- Classification requires multimodal approach (semiology + EEG + MRI + genetics)
- Focal spasms → consider early surgical evaluation, especially if spasms-specific therapy fails
- Terminology: “infantile spasms” → “epileptic spasms” (can occur at any age)
Unknown Onset Seizures
- Valid category when origin cannot be determined — can be reclassified when more data available
- Three types: preserved consciousness, impaired consciousness, bilateral tonic-clonic
- Epileptic spasms in this class are a descriptor, not a seizure type
💎 Board Pearl
- Consciousness = awareness (recall) + responsiveness (react) — if either is impaired, classify as impaired
- An aura IS a seizure — classified as focal preserved consciousness seizure with non-observable manifestations
- If a question says “patient has impaired awareness but intact responsiveness” or vice versa → classify as impaired consciousness (either component suffices)
- The 2025 classification is backward-compatible: “impaired awareness” converts directly to “impaired consciousness”; “motor seizure” = “observable manifestation”
- Epileptic spasms: generalized = seizure type; focal = descriptor — focal spasms warrant surgical evaluation
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