01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Useful classification preserves the whole chronological semiology rather than naming an event from its most dramatic phase. Under the 2025 ILAE system, a Focal seizure may be classified with preserved or impaired consciousness when both awareness and responsiveness can be assessed, and observable and non-observable manifestations are then described in sequence. The 2017 terms focal aware and focal impaired-awareness, and older terms such as simple partial, complex partial and secondary generalisation, should be recognised as legacy wording when interpreting previous records.
Generalised seizure types have distinctive temporal patterns. Typical absence causes abrupt brief interruption of awareness with immediate recovery and often generalised spike-wave activity; it is not simply any staring episode. Myoclonic seizures are very brief shock-like jerks, often shortly after waking in juvenile myoclonic epilepsy. Tonic seizures produce sustained stiffening, atonic seizures sudden loss of tone, and generalised tonic-clonic seizures bilateral tonic then clonic activity from onset. Spasms and seizures with mixed or uncertain features require age- and syndrome-specific expertise.
Classification can change as witness video, EEG, MRI, developmental history and longitudinal events accumulate. Epilepsy type remains a separate formulation—focal, generalized, combined generalized and focal, or unknown—with a separate aetiological formulation. An epilepsy specialist should resolve discordant electroclinical findings before high-risk long-term treatment.
Key points
- Use the 2025 ILAE main classes—Focal, Generalized, Unknown whether focal or generalized, and Unclassified—then apply supported classifiers and descriptors: consciousness where assessable, observable or non-observable manifestations, and the chronological evolution of the event.
- A Focal seizure begins in a network limited to one hemisphere. When assessable, classify consciousness as preserved or impaired—using both awareness and responsiveness—then describe observable and non-observable manifestations in the order they occurred.
- A focal to bilateral tonic-clonic seizure may look fully generalised once convulsions spread, so the aura, first head or eye deviation and initial unilateral movement are disproportionately informative.
- The Generalized class involves rapidly engaging bilateral networks and includes absence, myoclonic, tonic, atonic and generalized tonic-clonic seizures, often within a recognisable age-related epilepsy syndrome.
- Unknown whether focal or generalized is a legitimate provisional class when available evidence cannot distinguish the two; use Unclassified when the event is accepted as epileptic but available information does not permit a more specific class.
- Seizure type, epilepsy type and epilepsy syndrome are different levels: one person can have several seizure types within one defined syndrome.
- An EEG pattern can support and refine classification but should be reconciled with semiology; a focal discharge, generalised spike-wave or normal recording is not interpreted in isolation.
- Classification is safety-critical because narrow-spectrum sodium-channel medicines can aggravate absence or myoclonic seizures, while reproductive and interaction risks also shape the final choice.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
A brief stereotyped rising epigastric sensation, déjà vu, unilateral tingling, visual distortion or jerking with preserved consciousness supports the Focal class and can provide useful anatomical clues.
Behavioural arrest, loss of awareness or responsiveness, oral or manual automatisms and post-event confusion commonly occur in Focal seizures with impaired consciousness, although mimics require positive comparison.
Frequent abrupt pauses lasting seconds with a blank stare, possible eyelid flicker and immediate return to activity fit typical absence more than daydreaming or a focal event with postictal change.
Sudden brief bilateral upper-limb jerks, particularly after waking and worsened by sleep deprivation, may cause objects to be flung and should prompt direct questions about generalised tonic-clonic seizures.
Unwitnessed events, incomplete recordings or conflicting evidence can justify the provisional Unknown whether focal or generalized class; use Unclassified only when an epileptic seizure cannot be assigned more specifically.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Structured eyewitness history and event videoFirst step - Why
- Identify the earliest manifestation, consciousness and sequence needed to assign a seizure class and supported descriptors.
- Interpretation and limitations
- A lateralised aura or initial unilateral manifestation supports the Focal class; convincingly simultaneous bilateral activity may support the Generalized class. Later symmetry cannot recover information lost from an unwitnessed beginning.
- 02
Routine EEG with provoking procedures when agreed - Why
- Support seizure classification and identify an electroclinical epilepsy syndrome.
- Interpretation and limitations
- Focal epileptiform discharges support a focal network, while generalized spike-wave supports a generalized epilepsy type. Artefact, incidental findings and imperfect sensitivity demand interpretation alongside the clinical account.
- 03
Sleep-deprived or ambulatory EEG - Why
- Increase the chance of capturing interictal or clinical events when routine testing is non-diagnostic.
- Interpretation and limitations
- Sleep may activate epileptiform abnormalities, and prolonged recording can sample fluctuating symptoms. A further normal test still cannot exclude epilepsy, and event capture may reveal a mimic.
- 04
Epilepsy-protocol MRI - Why
- Look for a focal structural substrate and resolve discordance between semiology and EEG.
- Interpretation and limitations
- Focal cortical dysplasia, hippocampal sclerosis, tumour, vascular injury or previous trauma may determine focal classification and referral. Many generalised genetic epilepsies have structurally normal MRI.
- 05
Developmental, family and syndrome assessment - Why
- Link seizure types to age at onset, cognition, triggers and inheritance rather than treating each event as isolated.
- Interpretation and limitations
- Morning myoclonus, photosensitivity and adolescent tonic-clonic seizures form a different treatment context from late-onset Focal seizures with impaired consciousness, even if both culminate in convulsions.
04Clinical next stepsHow the result changes management or prompts escalation.
01DescribeCapture the earliest semiologyFirst stepA suspected epileptic event is being classified after immediate safety needs are met.+
- 11. Ask what the person experienced first, including sensory, emotional, cognitive, autonomic or motor symptoms before awareness changed.
- 22. Ask witnesses about responsiveness, eye and head direction, first moving body part, symmetry, sequence, duration and post-event behaviour without offering diagnostic labels.
- 33. Assign Focal, Generalized, Unknown whether focal or generalized, or Unclassified, then add consciousness and observable or non-observable descriptors only where supported and record manifestations in chronological order.
- 44. Preserve the raw description in the record so a later EEG or video can refine the category without being constrained by an early label.
02CorrelateBuild an electroclinical classificationInitial seizure description suggests epilepsy and testing is available.+
- 11. Compare semiology with routine EEG, recognising that discordance may reflect sampling, incorrect history, an incidental discharge or a more complex epilepsy type.
- 22. Use sleep-deprived or ambulatory EEG if diagnostic uncertainty persists and the additional yield could change treatment or safety advice.
- 33. Obtain MRI under an epilepsy protocol when indicated, especially when the Focal class is suspected, neurological findings are present or a previously stable pattern changes.
- 44. Formulate seizure type, epilepsy type, possible syndrome and likely aetiology separately, documenting which elements remain provisional.
03ApplyUse classification to avoid harmLong-term treatment or referral is being chosen.+
- 11. Select a medicine effective for the classified seizure type while accounting for age, comorbidity, pregnancy potential, interactions and the person’s priorities.
- 22. Avoid agents known to aggravate absence or myoclonic seizures when a generalised syndrome is possible, seeking specialist advice if classification is uncertain.
- 33. Revisit the diagnosis after treatment failure, a new seizure type or unexpected EEG and imaging results rather than simply stacking additional medicines.
- 44. Refer promptly for syndrome-specific or tertiary evaluation when seizures remain uncontrolled, the phenotype is mixed, or surgery and non-pharmacological treatments might be relevant.
05Procedure and medicine safetyRelevant preparation, treatment and contraindications.
Lamotrigine or levetiracetam for focal seizures
NICE advises either as first-line monotherapy; dosing is titrated from the current BNF and product guidance, with lamotrigine increased particularly slowly and according to interacting medicines.Lamotrigine can cause serious rash and has major titration interactions with valproate; levetiracetam may worsen irritability or mood. Pregnancy, renal function, adherence and psychiatric history influence selection.
Ethosuximide for isolated absence seizures
NICE recommends ethosuximide first line for absence seizures without other seizure types; start and titrate using age, weight, current formulary and specialist instructions.It does not cover generalised tonic-clonic seizures. Ask specifically about myoclonus and convulsions, and monitor gastrointestinal, neuropsychiatric, haematological or hepatic adverse effects as clinically indicated.
06Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Maintain a seizure record that distinguishes each event type, time of day, awareness, duration, recovery, injury and likely trigger rather than counting all episodes together.
- Review EEG and MRI concordance with the evolving clinical pattern, escalating unexpected focal findings or a changing semiology to the epilepsy service.
- After medicine initiation, monitor the specific target seizure type, adverse effects, adherence and any emergence or worsening of absence, myoclonus or convulsions.
- Reassess syndrome and reproductive safety at life-stage transitions, including adolescence, contraception planning, pregnancy intentions and older-age comorbidity.
- Evaluate ongoing events despite two appropriate tolerated regimens for drug-resistant epilepsy and timely tertiary referral rather than indefinite empirical substitutions.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Bilateral does not equal generalised
A focal seizure can spread rapidly to both hemispheres, so the first aura or lateralised sign is more classifying than the eventual bilateral convulsion.
Consciousness is operational
The Focal consciousness classifier uses both awareness and responsiveness. Inability to speak because of aphasia or motor arrest does not by itself establish impaired consciousness.
Absence ends abruptly
Immediate resumption of an interrupted activity after a very brief frequent pause favours typical absence, whereas longer post-event confusion is more suggestive of a Focal seizure with impaired consciousness.
Myoclonus needs direct questioning
People may describe morning jerks as clumsiness and never volunteer them, yet recognition can prevent prescription of medicines that aggravate a generalised syndrome.
Unknown is not a failure
A transparent provisional Unknown whether focal or generalized classification is safer than false precision and can be revised when video, EEG or later events add evidence.
08Common pitfallsFrequent interpretation and management errors.
- 01
Classifying every tonic-clonic seizure as Generalized ignores focal auras, initial unilateral manifestations and postictal deficits that change imaging and medication choices.
- 02
Treating any brief stare as absence can miss Focal seizures with impaired consciousness, inattention, sleep episodes or functional symptoms.
- 03
Using old labels inconsistently makes it unclear whether secondary generalisation describes onset, spread or a particular syndrome.
- 04
Letting one EEG override a persuasive event history risks both false-positive and false-negative classification.
- 05
Choosing carbamazepine before asking about morning jerks or absence events can exacerbate an unrecognised generalised epilepsy.