What are the observable seizure manifestations in the 2025 ILAE classification?

2025 ILAE Classification: Observable Seizure Manifestations

Core Classification Framework

The 2025 ILAE classification organizes seizures into four main classes and distinguishes between observable and non-observable manifestations, replacing the previous "motor" terminology to better reflect what can be clinically witnessed during seizure events. 1, 2

The four main seizure classes are:

• Focal seizures (originating within one cerebral hemisphere) 1, 2
• Generalized seizures (rapidly involving both hemispheres) 1, 2
• Unknown (whether focal or generalized) 1, 2
• Unclassified 1, 2

Observable vs. Non-Observable Features

The term "motor" has been replaced with "observable" manifestations to encompass all clinically witnessed seizure features, not just movement-based phenomena. 3 This represents a fundamental shift in how seizure semiology is conceptualized and documented.

Observable Manifestations Include:

Motor phenomena:

• Tonic activity - sudden stiffening of the body 4
• Clonic activity - symmetric, synchronous rhythmic jerking movements 4
• Myoclonic jerks - sudden, brief, shock-like muscle contractions that may be generalized, focal, or multifocal 5
• Negative myoclonus - now recognized as a distinct seizure type in the 2025 update 1, 3
• Automatisms - oral movements including chewing, smacking, and blinking 4
• Unilateral or partial limb movements 4

Non-motor observable features:

• Altered consciousness - defined by impaired awareness (inability to recall) and/or responsiveness 1, 2
• Behavioral arrest - cessation of activity characteristic of absence seizures 4
• Eye movements - including eye fluttering or deviation 4

Non-Observable Manifestations:

• Subjective sensory phenomena (auras) - rising abdominal sensation, unpleasant odors/tastes, déjà vu 4
• Electrographic-only seizures - detected solely by EEG without clinical correlate 5

Key Classification Updates for 2025

Six major revisions distinguish the 2025 classification from the 2017 version: 3

1. Removal of "onset" terminology from main seizure class names 3

2. Consciousness replaces "awareness" as the primary classifier, now defined by both awareness (recall) and responsiveness, assessed clinically 1, 2, 3

3. "Observable" replaces "motor" to better capture all witnessed seizure features 3

4. Chronological sequence of semiology is prioritized over first-noticed symptoms 1, 2, 3

5. Negative myoclonus is recognized as a new generalized seizure type 1, 3

6. Epileptic spasms are now used as a descriptor for focal and unknown seizures, while retained as a seizure type for generalized seizures 1, 3

Generalized Seizure Types with Observable Manifestations

Generalized seizures are categorized into three groups with direct treatment implications: 1

• Absence seizures - brief lapses in awareness, classified as non-motor generalized seizures 4
• Generalized tonic-clonic seizures - sequential tonic stiffening followed by clonic jerking 4
• Other generalized seizures - including tonic, clonic, myoclonic, myoclonic-tonic-clonic, myoclonic-atonic, atonic, and epileptic spasms 1, 2

Focal Seizure Observable Features

Focal seizures are classified by consciousness state (preserved or impaired) and observable manifestations: 1, 2

Timing characteristics that indicate focal epileptic origin:

• Movements beginning at the moment of consciousness loss (not after a delay, which suggests syncope) 4
• Numerous movements (often >100 vs. ~10 in syncope) 4
• Duration >1 minute (mean 74-90 seconds vs. ~20 seconds for syncope) 4
• Unilateral or asymmetric motor activity 4

Focal features in pediatric patients:

• Any focal semiological feature is independently associated with clinically relevant neuroimaging abnormalities 4
• Focal neurologic findings yield 50% positive CT rate vs. 6% when absent 4
• Recurrence rates reach 94% for focal seizures vs. 72% for generalized 4

Post-Cardiac Arrest Observable Manifestations

Myoclonus is the most common observable seizure type after cardiac arrest: 5, 4

• Presents as sudden, brief, shock-like involuntary muscle contractions 5
• Often generalized but may be focal (periodic eye-opening, swallowing, diaphragmatic contractions) or multifocal 5
• Typically develops within the first 1-2 days post-arrest 5, 4
• Most has cortical origin with time-locked EEG discharges or burst-suppression patterns 5, 4

Lance-Adams syndrome:

• Less frequent chronic myoclonus developing after consciousness recovery 5, 4
• Predominantly affects limbs, induced by purposeful actions or sensory stimulation 5, 4
• May become disabling and persist long-term 4

Distinguishing Epileptic from Non-Epileptic Observable Features

Psychogenic non-epileptic seizure characteristics: 4

• Eyes closed during unconsciousness 4
• Pelvic thrusting movements 4
• Waxing and waning intensity of movements 4
• Loss of consciousness >5 minutes 4
• Eye fluttering 4

Critical pitfall: Tongue biting and urinary incontinence are unreliable discriminators between epileptic seizures, syncope, and psychogenic events 4

Clinical Implementation

The classification provides two versions for different clinical contexts: 2

• Basic version - applicable in resource-limited or primary care settings, focusing on main seizure classes and observable vs. non-observable features 2
• Expanded version - offers detailed semiological descriptors with temporal sequence and somatotopic detail for advanced diagnostic and surgical decision-making 2

The system uses taxonomic rules distinguishing:

• Classifiers - reflect biological classes with direct clinical management impact 1
• Descriptors - indicate other important seizure characteristics 1