First seizure and seizure mimics

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

A seizure is a transient occurrence caused by abnormal excessive or synchronous neuronal activity. Epilepsy is an enduring tendency to recurrent unprovoked seizures and is not synonymous with a single convulsion. Acute symptomatic seizures occur in close association with an acute cerebral or systemic insult such as hypoglycaemia, major electrolyte disturbance, infection, stroke, head injury, intoxication or alcohol withdrawal. Identifying and correcting the provoking cause is urgent, but the patient may still need neurological assessment if the event or substrate creates continuing risk.

The event history should be chronological. Beforehand, ask about sleep deprivation, fever, pregnancy, medicines, missed doses, alcohol or drug use, head injury, aura, palpitations, posture, pain and emotional triggers. During the event, clarify responsiveness, eye and head position, colour, breathing, symmetry and sequence of movement, duration, vocalisation and injury. Afterwards, document confusion, sleep, headache, myalgia, weakness and time to baseline. Avoid asking only whether the person shook or was unconscious, because those labels collapse useful discriminating detail.

Important mimics include vasovagal and cardiac syncope, functional seizures, migraine aura, transient ischaemic attack, sleep disorders, movement disorders and metabolic encephalopathy. More than one condition can coexist. Emergency protocols, specialist diagnosis, current driving law and an individualised risk discussion remain essential.

Key points

The diagnosis rests first on a detailed account from the patient and witnesses, including before, during and after the event; obtain smartphone video when available and consent permits.
A first suspected seizure should prompt a 12-lead ECG because arrhythmia and convulsive syncope can closely resemble epilepsy and may carry immediate cardiac risk.
Check capillary glucose promptly and investigate sodium, calcium, infection, intoxication, withdrawal and other provoking factors according to the clinical context.
Lateral tongue injury, stereotyped tonic then clonic movements, cyanosis, prolonged post-event confusion and postictal focal weakness increase the probability of a tonic-clonic seizure but none is perfectly specific.
Presyncope, pallor, sweating, a situational trigger and rapid recovery favour syncope; brief jerks can occur during cerebral hypoperfusion and do not automatically imply epilepsy.
NICE recommends urgent referral after a first suspected seizure for assessment by an epilepsy-experienced clinician, aiming for review within two weeks.
When EEG is requested after a first seizure it should be performed as soon as possible, ideally within 72 hours; epileptiform activity supports the diagnosis, while a normal result cannot exclude it.
Do not start long-term antiseizure medication reflexively after every provoked or uncertain event; recurrence risk, imaging, EEG, neurological findings and the person’s preferences guide a specialist decision.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Acute provoked seizure

Hypoglycaemia, electrolyte disturbance, infection, stroke, trauma, intoxication or withdrawal can produce a time-linked seizure without establishing chronic epilepsy.

Structural cerebral disease

Previous infarction, tumour, cortical malformation, trauma or infection can create a persistent epileptogenic focus and raise recurrence risk.

Genetic or network epilepsy

A first recognised event may reveal an inherited generalised or focal epilepsy syndrome, often supported by age, semiology, EEG and family history.

Unknown cause

Some apparently unprovoked seizures remain unexplained after appropriate imaging and physiological assessment, requiring probability-based recurrence counselling.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Cortical hyperexcitability
A transient insult or enduring network abnormality shifts excitation above inhibition, allowing a population of cortical neurons to discharge synchronously.
2
Local or bilateral recruitment
Abnormal activity remains focal, impairs awareness or propagates through connected networks to produce bilateral tonic and clonic movement.
3
Postictal suppression
After discharge terminates, inhibitory and metabolic recovery causes confusion, sleepiness, headache or transient focal weakness that resolves over time.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Generalised convulsive eventRed flag

Abrupt loss of awareness followed by tonic stiffening and rhythmic bilateral clonic movements, with post-event confusion and muscle soreness, is strongly suggestive when witnessed as a coherent sequence.

Focal-class clueRed flag

A stereotyped sensory, experiential, autonomic or motor aura, unilateral onset, head version, speech arrest or postictal focal weakness suggests a seizure beginning in one cerebral network.

Convulsive syncopeRed flag

Prolonged standing, pain, heat, nausea, sweating, visual dimming and pallor followed by brief loss of tone, a few jerks and rapid orientation favours reflex syncope; exertional or supine collapse raises cardiac concern.

Functional seizure features

A prolonged fluctuating course, asynchronous movements, variable responsiveness or tightly closed eyes can support a functional event, but diagnosis requires positive expert assessment and no single sign is decisive.

Acute symptomatic seizureRed flag

Fever, meningism, severe metabolic disturbance, recent brain injury, stroke, intoxication or withdrawal points towards an immediate provoking process whose treatment cannot wait for an outpatient epilepsy label.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

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
Capillary glucose and targeted blood testsFirst step
Why
Find reversible metabolic causes and assess consequences of a prolonged convulsion.
Interpretation and limitations
Correct hypoglycaemia immediately. Electrolytes, renal and liver function, calcium, full blood count, inflammatory markers, toxicology or pregnancy testing are selected from the history; non-specific postictal abnormalities require clinical context.
02
Twelve-lead ECG
Why
Identify cardiac conditions that can cause transient loss of consciousness with convulsive movements.
Interpretation and limitations
Assess rhythm, conduction, QT interval, pre-excitation and ischaemic features. A normal resting tracing does not rule out intermittent arrhythmia, so concerning exertional, supine or family-history features require cardiac escalation.
03
Electroencephalography
Why
Support a clinical epilepsy diagnosis and help classify seizure type or syndrome.
Interpretation and limitations
Epileptiform discharges increase recurrence probability and can guide classification. A normal routine study never excludes epilepsy; sleep-deprived or ambulatory recording may be considered when uncertainty persists.
04
MRI brain using an epilepsy protocol
Why
Detect a structural substrate when epilepsy is diagnosed or a lesion is clinically suspected.
Interpretation and limitations
MRI is preferred for most people with diagnosed epilepsy, using regionally agreed protocols. Urgent CT is selected when an acute lesion, haemorrhage, trauma or contraindication makes it the appropriate immediate test.
05
Witness account or consented event video
Why
Preserve the semiology that is usually absent by the time clinicians assess the patient.
Interpretation and limitations
Ask the witness to describe rather than diagnose. Video can show onset, symmetry and responsiveness, but privacy, incomplete capture and the clinical circumstances must be considered.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Convulsive syncope

Presyncope, pallor, situational trigger and rapid recovery favour hypoperfusion; brief stiffening or jerks can occur and do not prove epilepsy.

Functional or dissociative seizure

Prolonged fluctuating movement, closed resistant eyes and variable responsiveness may support a functional event, ideally assessed through specialist semiology and video EEG.

Migraine aura or TIA

Gradually spreading positive symptoms favour aura, while abrupt negative focal loss suggests TIA; neither usually produces a stereotyped convulsion with prolonged postictal confusion.

Parasomnia or movement disorder

Events arising from sleep or recurrent dystonic, tremulous or tic-like movements require chronology, awareness and video evidence to separate them from seizures.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01ImmediateStabilise and identify provocationFirst stepA person presents during or soon after a first suspected seizure.

11. Protect from injury, use ABCDE, time the event, check glucose and oxygenation, and treat as status if convulsions reach five minutes or recovery fails.
22. Establish baseline cognition and repeat neurological examination after the postictal period, looking for trauma, meningism, pregnancy-related disease and persistent focal signs.
33. Obtain ECG and targeted laboratory tests, treating major metabolic, infectious, toxicological or withdrawal causes through the appropriate acute pathway.
44. Decide whether immediate CT, lumbar puncture, cardiac monitoring or admission is needed; do not defer dangerous-cause evaluation to the epilepsy clinic.

02ReconstructDistinguish seizure from mimicThe person is stable enough for a detailed account.

11. Build a timeline from pre-event symptoms and circumstances through motor sequence, responsiveness, colour, duration and recovery using patient and independent witness accounts.
22. Seek positive features supporting the Focal or Generalized class and actively compare syncope, functional events, migraine, sleep and movement phenomena.
33. Record uncertainty explicitly and avoid over-weighting isolated incontinence, tongue injury or serum biomarkers, which are supportive at most.
44. Ask about previous subtle episodes, febrile seizures, developmental or neurological history, family history and prior brain insults that alter recurrence probability.

03DischargeCreate a safe diagnostic bridgeNo acute admission indication remains after a suspected first seizure.

11. Refer urgently to a first-seizure or epilepsy-experienced clinician with the eyewitness description, ECG, results, medicines, images and contact details.
22. Give written advice about driving cessation and DVLA responsibility, bathing, swimming, heights, machinery, sleep, alcohol and what witnesses should do during recurrence.
33. Explain when to call emergency services, including a convulsion lasting five minutes, repeated events, serious injury, breathing difficulty or failure to recover as expected.
44. Let the specialist integrate timely EEG and neuroimaging with recurrence risk before long-term treatment, unless an acute indication has already been established.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Terminates a convulsion that has reached the threshold for emergency treatment rather than being used routinely after a brief self-terminating event.

Buccal midazolam for a prolonged convulsive seizure

Use the person’s emergency plan where available; a common adult community rescue dose is 10 mg buccally, while hospital benzodiazepine choice and repeat timing follow the current status protocol.

Support airway and breathing, time each dose and avoid repeated unrecorded benzodiazepines because respiratory depression and delayed escalation can follow. Call emergency services under the agreed plan.

Reduces recurrence when the balance of future seizure harm and treatment burden favours intervention after shared discussion.

Long-term antiseizure treatment after one unprovoked event

There is no universal starter regimen; a specialist selects a seizure-appropriate medicine and titration when neurological deficit, unequivocal epileptiform EEG, structural abnormality or unacceptable recurrence risk supports treatment.

Do not treat an uncertain mimic merely to feel safe. Consider mood, cognition, pregnancy potential, contraception, organ function, interactions, occupation and driving, and explain that abrupt later withdrawal may provoke seizures.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Trauma and aspiration

Loss of awareness and motor control causes head injury, fractures, burns or drowning, while vomiting and reduced consciousness threaten the airway.

Status epilepticus

Failure of the event to stop or rapid recurrence without recovery produces cardiorespiratory, metabolic and neuronal injury requiring emergency treatment.

Recurrence and epilepsy-related death

An enduring epileptic tendency can cause further seizures, and uncontrolled tonic–clonic events contribute materially to sudden unexpected death risk.

Driving and occupational restriction

Even one seizure can temporarily prevent driving or hazardous work and create financial, safeguarding and psychological consequences while diagnosis remains uncertain.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Confirm return to neurological and cognitive baseline; persistent confusion or weakness requires reassessment for non-convulsive status, stroke, infection, injury or another acute lesion.
Track completion and interpretation of ECG, specialist review, EEG and indicated imaging rather than assuming a referral alone closes the diagnostic loop.
Document further events with timing, witness description, recovery and possible triggers, encouraging safe video capture only when care and privacy are not compromised.
If medication is started, monitor seizure recurrence, adherence, adverse effects, mood, interactions and syndrome-specific laboratory or serum-level needs.
Revisit driving, occupational and domestic safety at each diagnostic change, particularly if another event occurs or treatment is altered.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Jerks occur in syncope

Brief myoclonic movements can accompany cerebral hypoperfusion, so the prodrome, colour, loss of tone and speed of recovery often discriminate better than shaking alone.

Tongue site adds weight

Lateral tongue trauma supports a generalised convulsion more than a non-specific tip injury, but absence of a bite cannot exclude seizure.

Postictal weakness localises

Todd paresis can persist after a focal seizure and mimic stroke; because acute stroke can itself trigger seizure, new persistent weakness still needs urgent imaging.

EEG supports a story

Interictal epileptiform activity meaningfully raises diagnostic confidence, yet incidental abnormalities and normal recordings mean EEG never replaces expert clinical history.

Provoked does not mean trivial

An acute symptomatic seizure may have a lower long-term recurrence tendency than an unprovoked event, while the underlying sepsis, metabolic failure or brain lesion may be immediately life-threatening.

11Common pitfallsFrequent interpretation and management errors.

01
Diagnosing epilepsy from one unexplained blackout without an ECG can miss an intermittent channelopathy or arrhythmia with preventable sudden-death risk.
02
Using urinary incontinence or a raised lactate as a stand-alone diagnostic test overstates non-specific findings that occur in several causes of collapse.
03
Reassuring a patient that a normal routine EEG rules out epilepsy contradicts the limited sensitivity of interictal recording.
04
Starting antiseizure medication before clarifying the seizure class and epilepsy type can worsen some syndromes and adds adverse effects to a possible mimic.
05
Discharging without driving and recurrence safety advice leaves a substantial interval of unmanaged risk before the specialist appointment.