Auras and Epilepsy
How Epilepsy Is Actually Diagnosed
Why there is no single test that can prove or rule out epilepsy
Epilepsy is not diagnosed by one blood test, one brain scan or one EEG result.
Diagnosis usually comes from assembling several pieces of evidence:
what happened before the event
what happened during it
what happened afterwards
eyewitness descriptions
video footage where available
medical and family history
physical and neurological examination
ECG
blood tests
EEG
MRI
and, when necessary, more specialist investigations.
NICE states that after a first suspected seizure, clinicians should take a detailed history, use eyewitness accounts and video footage where possible, examine the person and consider conditions that can mimic epilepsy.
The diagnosis is therefore best thought of as a clinical investigation, not a test that someone either passes or fails.
A seizure and epilepsy are not the same thing
A person can have an epileptic seizure without necessarily having epilepsy.
A seizure is an event caused by abnormal excessive or synchronised electrical activity in the brain.
Epilepsy refers to an enduring tendency to have epileptic seizures.
The International League Against Epilepsy — ILAE — currently defines epilepsy as being present when one of the following applies:
At least two unprovoked or reflex seizures occurring more than 24 hours apart.
One unprovoked or reflex seizure with a sufficiently high risk of further seizures — broadly equivalent to at least a 60% probability over the following 10 years.
Diagnosis of an epilepsy syndrome.
So the old idea that:
“You need two seizures before anyone can diagnose epilepsy”
is not always correct.
Some people can meet the definition after one seizure when other evidence indicates a high continuing risk.
What is an unprovoked seizure?
An unprovoked seizure occurs without an immediate temporary cause that adequately explains it.
This is different from an acute symptomatic seizure, which occurs because the brain is being temporarily affected by another acute problem.
Examples can include:
severe hypoglycaemia
major electrolyte disturbance
acute brain infection
acute stroke
certain toxic exposures
or severe alcohol withdrawal.
If the underlying temporary problem is corrected and there is no continuing tendency to have seizures, the person may not have epilepsy.
The distinction is important because treatment and future seizure risk can be very different.
Reflex seizures can still be epilepsy
The word “provoked” can sometimes cause confusion.
A seizure triggered by a specific stimulus such as flashing lights does not necessarily mean it is an acute symptomatic seizure.
Someone with recurrent photosensitive reflex seizures, for example, may have epilepsy because their brain has an enduring susceptibility to seizures when exposed to that stimulus.
The ILAE definition specifically includes recurrent reflex seizures within epilepsy.
What happens after a first suspected seizure?
Current NICE guidance says children, young people and adults should be referred urgently after a first suspected seizure, with a specialist appointment intended within 2 weeks.
Adults should be assessed by a clinician experienced in first seizures and epilepsy diagnosis. Children and young people should be assessed by a paediatric clinician with appropriate expertise.
The purpose is not simply to decide:
“Was that a seizure?”
The specialist also needs to ask:
Was it epileptic?
Could something else explain it?
Was there an immediate provoking cause?
What type of seizure was it?
Is there evidence of an epilepsy syndrome?
How likely is another seizure?
What investigations are needed?
Does treatment need to start?
The story is one of the most important diagnostic tests
A first-seizure appointment is often dominated by questions.
That is deliberate.
UCLH describes a detailed, accurate account of what happened as the most important part of first-seizure assessment.
The specialist may ask what happened:
Before the event
For example:
Were there unusual sensations?
Déjà vu?
A strange smell or taste?
Sudden fear?
Visual disturbance?
Dizziness?
Nausea?
Palpitations?
Light-headedness?
Was the person standing for a long time?
Had they just stood up?
Were they ill, dehydrated or in pain?
Had they been asleep?
During the event
For example:
Did awareness change?
Could the person respond?
Did they fall?
Did the body stiffen?
Were there rhythmic jerks?
Was one side affected first?
Did the head or eyes turn?
Did the person make repetitive movements?
Did they speak?
Was there unusual behaviour?
What happened to breathing?
How long did it last?
Afterwards
For example:
Was there confusion?
Sleepiness?
Agitation?
Headache?
Weakness?
Memory loss?
Speech difficulty?
Muscle pain?
Injury?
How long did recovery take?
The sequence matters.
A seizure is often recognised not by one dramatic feature, but by the pattern before, during and after the event.
Why eyewitnesses matter
Someone having a seizure may not know everything that happened.
They may:
lose consciousness
have impaired consciousness
lose memory for the event
remember only the aura
or remember the beginning but not the rest.
An eyewitness can therefore provide information the person cannot.
NICE specifically recommends using eyewitness accounts where possible.
Useful witnesses may describe:
how the event started
which body part moved first
whether the eyes were open
whether the person responded
the sequence of movements
skin colour
breathing
duration
and recovery.
If the witness cannot attend, a written description can still be useful.
Video can be extremely helpful
A safely recorded phone video can give a specialist information that is difficult to capture in words.
NICE recommends using video footage where possible, and Epilepsy Action advises that videos of habitual events can help doctors reach the correct diagnosis.
Safety comes first.
Do not:
delay seizure first aid
leave someone in danger
or concentrate on filming instead of getting emergency help.
But when another person can safely record an event, even a short clip can show:
movement pattern
responsiveness
breathing
eye and head position
automatisms
and recovery behaviour.
A diagnosis should not be based on one feature
There is no single physical sign that always proves an epileptic seizure occurred.
For example:
shaking can occur during epilepsy, but also during fainting and functional seizures;
urinary incontinence can occur during seizures but is not specific to epilepsy;
tongue injury can support the possibility of a convulsive seizure but is not present in every seizure;
confusion can follow epilepsy but can also have other causes.
Clinicians therefore look at the combination and sequence of features rather than relying on one sign.
Many conditions can look like epilepsy
Part of epilepsy diagnosis is actively looking for other explanations.
Conditions that may mimic some epileptic seizures include:
fainting — syncope
abnormal heart rhythms
functional or dissociative seizures
migraine
sleep disorders
movement disorders
panic attacks
metabolic disturbances
some medication or substance effects
and other neurological conditions.
NHS and Epilepsy Action both emphasise that having a seizure-like event does not automatically mean someone has epilepsy.
Fainting can include jerking
One common misconception is:
“They were shaking, so it could not have been a faint.”
In fact, reduced blood flow to the brain during syncope can sometimes produce:
stiffening
brief jerks
eye movements
or other seizure-like movements.
This is one reason the circumstances surrounding a collapse are so important.
Features such as:
prolonged standing
heat
pain
dehydration
nausea
sweating
greying vision
or rapid recovery after lying flat
may support syncope, although diagnosis still requires clinical assessment.
An NHS first-seizure service specifically warns that fainting and other collapses can resemble epileptic seizures.
Why everyone with a first suspected seizure should have an ECG
An electrocardiogram, or ECG, records electrical activity from the heart.
Some abnormal heart rhythms can cause sudden loss of consciousness.
The resulting collapse may sometimes resemble an epileptic seizure.
NICE therefore recommends a 12-lead ECG after a first suspected seizure to help identify cardiac causes that can mimic epilepsy.
An ECG does not test for epilepsy.
Its job is to make sure an important alternative explanation is not missed.
Blood tests can look for provoking causes
There is no routine blood test that says:
“This person has epilepsy.”
Blood tests are usually looking for other explanations or factors.
Depending on the circumstances, doctors may check:
blood glucose
sodium
calcium
other electrolytes
kidney function
liver function
infection markers
blood cells
medication levels
or toxicological causes.
NICE specifically highlights metabolic disturbances such as hypoglycaemia as possible causes of seizures.
Related Information Hub page:
Blood Tests, Lumbar Puncture and Antibody Testing in Epilepsy
EEG supports the diagnosis — it does not make the diagnosis alone
An EEG records electrical activity from the brain.
If the history suggests an epileptic seizure and epilepsy is suspected, NICE recommends considering a routine awake EEG to:
support the diagnosis
help classify seizure type
and help identify an epilepsy syndrome.
If requested after a first seizure, NICE recommends performing it as soon as possible, ideally within 72 hours.
But there is one particularly important rule:
A normal EEG does not rule out epilepsy
NICE explicitly says:
Do not use EEG to exclude a diagnosis of epilepsy.
Routine EEG has relatively low sensitivity.
Epileptiform activity may simply not occur during the short recording.
This means someone can have genuine epilepsy while:
the routine EEG is normal
the sleep EEG is normal
or even several EEGs have been unrevealing.
An abnormal EEG does not automatically prove epilepsy either
An EEG showing clear epileptiform abnormalities can provide strong supporting evidence.
But EEG findings still need to fit the clinical history.
Some people without recognised epileptic seizures can have unusual EEG findings.
Artefacts can also be misinterpreted.
Epilepsy Action notes that incorrect EEG interpretation is one recognised cause of epilepsy misdiagnosis.
The test should therefore be interpreted by appropriately trained specialists.
Related Information Hub page:
EEG: What It Can — and Cannot — Tell You About Epilepsy
What happens if the first EEG is normal?
If suspicion of epilepsy remains, NICE recommends considering a sleep-deprived EEG.
If routine and sleep-deprived EEG remain normal and diagnostic uncertainty continues, NICE recommends considering ambulatory EEG for up to 48 hours.
Some people may later require:
prolonged video EEG
inpatient video telemetry
home video telemetry
or specialist invasive recordings.
The choice depends on the question doctors are trying to answer.
MRI looks for structural causes
MRI does something completely different from EEG.
An EEG asks:
What is the brain's electrical activity doing?
MRI asks:
What does the brain's structure look like?
MRI may reveal abnormalities associated with epilepsy such as:
hippocampal sclerosis
focal cortical dysplasia
previous stroke
old brain injury
developmental abnormalities
vascular lesions
tumours
or other structural causes.
NICE recommends epilepsy-protocol MRI for most people diagnosed with epilepsy, with exceptions for some recognised epilepsy syndromes.
A normal MRI does not rule out epilepsy
Many people with epilepsy have structurally normal MRI scans.
Possible reasons include:
epilepsy without a structural lesion
genetic mechanisms
abnormalities too small to detect
subtle cortical abnormalities
network dysfunction
or limitations of the scan or protocol.
MRI is therefore investigating why epilepsy may be happening, not simply determining whether epilepsy exists.
Related Information Hub page:
MRI and Epilepsy: What Doctors Are Looking For
Why CT may sometimes be used
CT can be valuable in emergencies because it is fast and can identify problems such as:
acute bleeding
significant head injury
large structural lesions
or some other urgent causes.
For detailed long-term structural epilepsy investigation, MRI is generally preferred.
NICE recommends considering CT when MRI cannot be performed.
What happens when doctors actually record one of the events?
Capturing a habitual event during simultaneous video and EEG can provide particularly powerful evidence.
Video telemetry allows clinicians to compare:
behaviour
responsiveness
movement
speech
recovery
and brain electrical activity
at exactly the same time.
This can help determine:
whether an event is epileptic
what type of seizure it is
whether different reported events are actually different
and, in focal epilepsy, where activity may begin.
It can also reveal seizures that the person did not know were happening.
Related Information Hub page:
Video Telemetry: Recording Seizures in Hospital
Functional seizures are real — but they are not epileptic seizures
Some people experience functional seizures, also called dissociative seizures or functional neurological seizures.
The events are real and involuntary, but they are not caused by the abnormal epileptic electrical activity responsible for epileptic seizures.
Video EEG recording of a typical event is particularly useful when this diagnosis is being considered.
Importantly, some people have:
epilepsy
functional seizures
or both.
So diagnosing one event type does not necessarily explain every event a person experiences.
Why doctors ask whether there is more than one seizure type
Someone may say:
“I have seizures.”
But they may actually experience several distinct events.
For example:
brief staring episodes
nocturnal stiffening
focal sensory events
and occasional bilateral tonic-clonic seizures.
Doctors need to determine whether these represent:
different phases of the same seizure type
multiple epileptic seizure types
or a mixture of epileptic and non-epileptic events.
Separating them can significantly affect treatment.
Classifying the seizure comes after deciding it was epileptic
Once clinicians believe an event was an epileptic seizure, they try to classify it.
The ILAE updated its operational seizure classification in 2025.
The four main classes are now:
Focal
Generalized
Unknown whether focal or generalized
Unclassified
What is a focal seizure?
A focal seizure begins within brain networks limited initially to one hemisphere.
That does not mean it necessarily remains confined there.
Focal seizures can spread through wider networks and can eventually involve both hemispheres.
The 2025 ILAE classification can further describe focal seizures according to features including the person's state of consciousness and the manifestations occurring during the seizure.
What is a generalised seizure?
Generalised seizures arise within and rapidly engage bilaterally distributed brain networks.
This does not mean every cell in the brain becomes involved simultaneously.
Generalised seizures can also appear asymmetrical.
Examples of generalised seizure types include forms of:
absence
myoclonic
tonic
clonic
atonic
and tonic-clonic seizures.
What does “unknown whether focal or generalised” mean?
Sometimes clinicians know an event was epileptic but do not yet have enough evidence to decide whether it was focal or generalised.
Rather than forcing it into the wrong category, the ILAE allows classification as:
Unknown whether focal or generalized.
More information may later allow reclassification.
That information might come from:
another witnessed seizure
video
EEG
telemetry
or MRI.
Unclassified does not mean the doctors think nothing happened
An unclassified epileptic seizure means clinicians believe the event was epileptic but do not have sufficient information to classify it more specifically.
This is different from diagnostic uncertainty about whether the event was epileptic at all.
Classification can change as better information becomes available.
Seizure type is not the same as epilepsy type
Once seizures have been classified, specialists may then classify the broader epilepsy.
Epilepsy may be:
focal
generalised
combined generalised and focal
or of uncertain type.
Clinicians may then determine whether the person fits a recognised epilepsy syndrome.
An epilepsy syndrome combines features such as:
age of onset
particular seizure types
EEG characteristics
triggers
developmental profile
genetics
imaging
and expected natural history.
The ILAE maintains recognised diagnostic criteria for epilepsy syndromes.
Why the syndrome matters
The diagnosis:
“epilepsy”
is often only the beginning.
Knowing the syndrome can influence:
which medicines are likely to work
which medicines may worsen seizures
whether genetic testing is useful
prognosis
risk of particular seizure types
and whether epilepsy may remit with age.
Examples include:
childhood absence epilepsy
juvenile absence epilepsy
juvenile myoclonic epilepsy
Dravet syndrome
and other recognised syndromes.
Doctors also try to identify the cause
Modern epilepsy diagnosis includes asking about aetiology — the underlying cause.
Possible categories include:
structural
genetic
infectious
metabolic
immune
or unknown.
More than one category can sometimes apply.
For example, a genetic condition may cause a structural brain abnormality.
Finding the cause can affect treatment as much as classifying the seizure itself.
When genetic testing may be needed
Genetic testing can sometimes identify a cause, especially in particular situations such as:
very early-onset epilepsy
developmental difficulties
recognised genetic epilepsy syndromes
autism or intellectual disability accompanying epilepsy
particular brain abnormalities
or unexplained cognitive decline.
A genetic result can occasionally directly influence treatment.
Related Information Hub page:
Genetic Testing and Epilepsy
When lumbar puncture or antibody testing may be needed
Most people being assessed for ordinary epilepsy do not require lumbar puncture.
These investigations become important when doctors suspect conditions such as:
encephalitis
meningitis
autoimmune brain inflammation
or another central nervous system disorder.
New seizures accompanied by rapidly developing:
confusion
memory deterioration
behavioural changes
psychiatric symptoms
fever
movement abnormalities
or reduced consciousness
may prompt a different investigation pathway.
Related Information Hub page:
Blood Tests, Lumbar Puncture and Antibody Testing in Epilepsy
Why neuropsychological testing may be used
Neuropsychological testing examines functions including:
memory
language
attention
processing speed
executive functions
and learning.
It can help when:
cognitive problems need investigating
epilepsy surgery is being considered
doctors need a baseline
or the pattern may provide additional information about affected brain networks.
Related Information Hub page:
Neuropsychological Testing and Epilepsy
Why some people need PET, SPECT or MEG
Most people never require these tests.
They are mainly used when epilepsy is difficult to localise or when surgery is being considered.
They can provide additional information about:
brain metabolism — PET
seizure-related blood flow — SPECT
or magnetic fields generated by brain activity — MEG.
They do not replace MRI or EEG.
They add another piece to complex cases.
Related Information Hub page:
PET, SPECT and MEG in Epilepsy
Why several tests may disagree
Epilepsy involves dynamic brain networks.
Different tests measure different things.
For example:
EEG measures electrical activity
MRI measures structure
PET measures metabolism
SPECT measures blood flow
MEG measures magnetic fields associated with neuronal activity
neuropsychology measures cognitive performance.
It is therefore possible for:
MRI to be normal while EEG is abnormal;
MRI to show a lesion while routine EEG is normal;
scalp EEG to appear widespread even though a seizure began focally;
or different investigations to point towards different regions.
Disagreement does not automatically mean one test was “wrong”.
It may reveal that the epilepsy network is more complicated than initially thought.
Why doctors like tests to agree
When several independent pieces of evidence point towards the same explanation, diagnostic confidence increases.
For example:
seizures begin with a consistent temporal-lobe aura;
video telemetry records focal temporal seizures;
EEG abnormalities are predominantly left temporal;
MRI shows left hippocampal sclerosis.
That evidence is concordant.
Concordance becomes especially important when invasive treatments such as epilepsy surgery are being considered.
A normal set of tests does not necessarily mean no epilepsy
This deserves repeating.
Someone can have:
normal blood tests
normal ECG
normal MRI
normal routine EEG
and still have epilepsy.
Epilepsy Action explicitly notes that some people are diagnosed based primarily on their symptoms and clinical history even when tests do not show an abnormality.
Tests sample particular aspects of brain function.
They are not perfect epilepsy detectors.
But symptoms alone must still be interpreted carefully
The opposite is also true.
A dramatic event does not automatically mean epilepsy.
The clinician still needs to consider:
syncope
cardiac disease
functional seizures
sleep disorders
metabolic problems
migraine
and other neurological conditions.
Good epilepsy diagnosis involves being confident enough to diagnose epilepsy when evidence supports it — but also being willing to reconsider when it does not.
Can epilepsy be misdiagnosed?
Yes.
Epilepsy can be:
missed
diagnosed late
or diagnosed incorrectly.
Reasons can include:
incomplete witness information
subtle focal seizures
normal routine EEG
seizure-like fainting
functional seizures
unusual sleep events
incorrect EEG interpretation
or several different event types occurring in the same person.
This is one reason specialist assessment is important.
A diagnosis can legitimately change
A diagnosis being revised does not always mean the first doctor was careless.
Sometimes new evidence becomes available.
For example:
another event is filmed;
prolonged video EEG captures a typical episode;
MRI reveals a subtle lesion;
a genetic result becomes available;
or several different types of event are finally recorded.
A person's diagnosis may therefore become more specific over time.
It might change from:
“possible epilepsy”
to:
“focal epilepsy”
and later to:
“temporal lobe epilepsy associated with a particular structural cause.”
Greater precision can improve treatment.
Why seizure diaries matter
A seizure diary can record:
date and time
what happened
warning symptoms
seizure duration
recovery
possible triggers
sleep
medication changes
menstrual cycle where relevant
and injuries.
Epilepsy Action recommends bringing a seizure diary to appointments because it can assist both diagnosis and treatment decisions.
A diary is particularly helpful for identifying repeated patterns that may not be obvious from memory alone.
Seizure diaries are not perfect counts
Someone may not recognise every seizure.
This is particularly true for:
sleep seizures
absence seizures
focal seizures with impaired consciousness
or events followed by amnesia.
A diary therefore records known events, not necessarily every seizure occurring in the brain.
Video telemetry can sometimes demonstrate that seizure burden was higher than anyone realised.
Questions to prepare before a first-seizure appointment
Useful information includes:
What was I doing immediately beforehand?
Was I awake or asleep?
Did I have any warning?
What did the witness see first?
Did I respond?
Did one side move before the other?
Did I stiffen?
Did I jerk?
What happened to my eyes or head?
How long did it last?
Was my breathing different?
What happened afterwards?
How long before I was back to normal?
Have I had smaller or unusual events before?
Has anything similar happened during sleep?
Is there epilepsy in my family?
Take:
a medication list
seizure diary
videos
witness description
ambulance or hospital records if available
and a list of questions.
Questions to ask the specialist
Useful questions include:
Do you think this was an epileptic seizure?
What else could explain it?
Was it provoked or unprovoked?
Do I meet the definition of epilepsy yet?
What type of seizure do you think it was?
Could it have been focal?
Do I need an EEG?
If my EEG is normal, what happens next?
Do I need an MRI?
Why was an ECG performed?
Are any blood abnormalities relevant?
Do I fit a recognised epilepsy syndrome?
Do you know the likely cause?
What is my risk of another seizure?
Do I need treatment now?
Diagnosis and treatment are separate decisions
Receiving an epilepsy diagnosis does not automatically dictate one particular treatment.
Likewise, clinicians may sometimes recommend treatment after a first seizure when the recurrence risk is sufficiently high.
The ILAE specifically distinguishes the definition of epilepsy from the decision about whether treatment should begin.
Treatment decisions consider factors such as:
seizure type
recurrence risk
EEG
MRI
underlying cause
injury risk
individual circumstances
reproductive considerations
medication risks
and the person's preferences.
The most important message
Epilepsy is not diagnosed by one test.
The most important evidence often begins with the event itself:
What happened before, during and after it?
Doctors then build the diagnosis using:
eyewitness descriptions
video
medical history
examination
ECG
blood tests
EEG
MRI
and specialist investigations when needed.
A normal EEG does not rule out epilepsy.
A normal MRI does not rule out epilepsy.
An abnormal EEG does not automatically prove epilepsy.
And having one seizure does not automatically mean someone has epilepsy.
The goal is to answer several questions:
Was the event epileptic?
Was it provoked or unprovoked?
What type of seizure was it?
Does the person meet the definition of epilepsy?
What type of epilepsy do they have?
Is there a recognised syndrome?
What caused it?
Getting those answers right matters because the correct diagnosis determines what treatment, investigation and support should come next.
Sources and further reading
NICE — Epilepsies in children, young people and adults (NG217): Diagnosis and assessment.
Current NICE guidance covers urgent referral after a first suspected seizure, history and eyewitness evidence, ECG, metabolic causes, EEG, MRI and further testing. Last updated January 2025.
NICE — Evidence and rationale for epilepsy diagnosis.
NICE explains that witness reports and videos improve expert clinical diagnosis, routine EEG has insufficient sensitivity to exclude epilepsy, and imaging should investigate structural causes rather than act as a standalone epilepsy test.
International League Against Epilepsy — Practical clinical definition of epilepsy.
The ILAE definition includes two unprovoked seizures more than 24 hours apart, one unprovoked seizure with a sufficiently high predicted recurrence risk, or diagnosis of an epilepsy syndrome.
International League Against Epilepsy — Updated classification of epileptic seizures, 2025.
The current classification uses four main seizure classes: focal, generalized, unknown whether focal or generalized, and unclassified.
NHS — Epilepsy.
Current NHS patient guidance explains the roles of specialist assessment, EEG, ECG, MRI/CT, blood tests and genetic testing, and notes that a seizure does not automatically mean epilepsy.
Epilepsy Action — Diagnosis.
UK information covering first-seizure assessment, witness descriptions, video, ECG, EEG, MRI, blood tests and genetic testing.
Information reviewed: September 2026.
This page provides general educational information. A first suspected seizure or a significant change in established seizures should be assessed by an appropriate healthcare professional.
