Diagnosis and Tests – Epilepsy: The Untold Side

Epilepsy is a clinical diagnosis. No single blood test, scan or EEG can diagnose every case, and normal test results do not automatically rule epilepsy out. The most important evidence is often the detailed story of what happened before, during and after the event, supported by examination and targeted investigations.

Worldwide context: the underlying diagnostic principles are international, but access to EEG, MRI, prolonged monitoring, genetic testing and specialist epilepsy services varies greatly between countries and regions. Where this page cites NICE, it is describing a specific UK guideline pathway rather than a universal rule for every health system.

The diagnosis starts with the event itself

After a first suspected seizure, NICE recommends urgent specialist assessment. A clinician will usually ask about warning symptoms, awareness, responsiveness, movements, breathing, colour change, injuries, tongue biting, loss of bladder control, duration and the recovery period. What happened afterwards can be as informative as what happened during the event.

Eyewitness descriptions are valuable, and safely obtained phone or home-video footage can sometimes provide important clues. However, neither a witness account nor a video should be treated as a stand-alone diagnostic test.

A seizure is not automatically epilepsy

A first seizure has several possible explanations. Some seizures are provoked by acute problems such as hypoglycaemia, infection, metabolic disturbance, alcohol or drug-related factors, or an acute brain injury. Other conditions can imitate epileptic seizures, including syncope, some cardiac rhythm disorders, sleep disorders, migraine and functional or dissociative seizures.

This is why the aim of assessment is broader than asking, “Was this a seizure?” Clinicians also need to ask what type of seizure it may have been, whether the person meets criteria for epilepsy, what the likely cause is, and whether a particular epilepsy syndrome can be identified.

EEG: useful evidence, but not a pass-or-fail test

An electroencephalogram (EEG) records electrical activity from the brain using electrodes placed on the scalp. If the clinical history suggests an epileptic seizure and epilepsy is suspected, NICE recommends considering a routine awake EEG to support the diagnosis and help identify seizure type or an epilepsy syndrome.

A normal EEG does not rule out epilepsy. Routine EEG has limited sensitivity because epileptiform activity may be intermittent and may not appear during a short recording. NICE specifically says EEG should not be used to exclude the diagnosis.

Equally, an EEG finding has to be interpreted in context. EEG supports the clinical assessment; it does not replace it. Misinterpreting normal variants or non-specific abnormalities can contribute to an incorrect epilepsy diagnosis.

Routine awake EEG

This is often the first EEG used. If an EEG is requested after a first seizure, NICE recommends performing it as soon as possible, ideally within 72 hours. During the test, activation procedures such as hyperventilation or flashing lights may be offered where appropriate after the benefits and risks are discussed.

Sleep-deprived EEG

If a routine EEG is normal but diagnostic uncertainty remains, a sleep-deprived EEG may be considered. Sleep and sleep deprivation can increase the chance of revealing epileptiform abnormalities in some epilepsies.

Ambulatory EEG

If routine and sleep-deprived EEGs are normal and uncertainty persists, NICE recommends considering ambulatory EEG for up to 48 hours. This allows a longer sample of brain activity during ordinary daily life and sleep.

Video-EEG telemetry

Long-term video-EEG records behaviour on video at the same time as EEG activity. It can be particularly useful when recurrent episodes remain unexplained, when clinicians need to distinguish epileptic from non-epileptic events, or as part of complex epilepsy and presurgical assessment. Capturing a person’s typical event with simultaneous EEG can provide information that a short routine EEG cannot.

MRI: looking for a structural cause

MRI does not diagnose epilepsy by itself. Its role is to look for structural brain abnormalities that may explain why seizures are occurring. These can include hippocampal sclerosis, focal cortical dysplasia, previous brain injury, stroke, vascular abnormalities, developmental changes, tumours and other lesions.

NICE recommends MRI for most people diagnosed with epilepsy, with exceptions for certain epilepsy types, and says it should follow a regionally agreed epilepsy MRI protocol. An epilepsy protocol uses a planned set of sequences designed to improve the chance of detecting abnormalities relevant to epilepsy. A standard brain MRI and an epilepsy-protocol MRI are therefore not necessarily equivalent investigations.

A normal MRI does not mean the epilepsy is not real. Some epilepsies have no visible structural lesion, and subtle abnormalities can sometimes be missed on an initial or non-specialist scan. NICE advises specialist neuroradiology review when seizures continue despite treatment and the diagnosis remains unclear, and repeat MRI may be considered if the first scan was suboptimal, features have changed or epilepsy surgery is being considered.

CT scanning

CT is faster and can be useful in acute situations, particularly when urgent causes such as bleeding or major injury are a concern. For longer-term structural assessment of epilepsy, MRI usually provides much greater detail. NICE recommends considering CT when MRI is contraindicated.

ECG: checking for cardiac mimics

NICE recommends a 12-lead ECG after a first suspected seizure. This matters because some heart rhythm disorders and episodes of syncope can cause sudden collapse, jerking or loss of consciousness that can resemble epilepsy. Identifying a cardiac cause can completely change the investigation and treatment pathway.

Blood tests

Blood tests do not usually diagnose epilepsy. They are used to look for conditions that can provoke seizures or affect management, such as abnormalities in blood glucose, sodium or other metabolic measures, infection or organ-function problems. Which tests are needed depends on the clinical circumstances.

Genetic testing

Genetics is increasingly important in epilepsy, but testing is targeted rather than automatically offered to everyone. A genetic diagnosis can sometimes explain the cause, clarify an epilepsy syndrome, inform prognosis, guide counselling and, in selected conditions, influence treatment choices.

NICE recommends considering genomic testing particularly in epilepsy of unknown cause with very early onset, features of a recognised genetic epilepsy syndrome, or additional features such as learning disability, autism, congenital abnormalities or unexplained cognitive or memory decline. Genetic counselling and informed consent are an important part of this process.

Read more: Genetics & Epilepsy →

Autoimmune and antibody testing

Some new-onset seizure disorders are caused by autoimmune inflammation of the brain. NICE recommends considering antibody testing, in discussion with a neurologist, when autoimmune encephalitis is suspected. This is not a routine test for every person with epilepsy.

Neuropsychological assessment

Neuropsychology examines cognitive functions such as memory, language, attention, processing speed and executive skills. It can help document how epilepsy, an underlying brain disorder or treatment is affecting cognition. In tertiary epilepsy services it is also an important part of presurgical assessment, helping clinicians understand patterns of brain function and the potential cognitive risks of an operation.

Neuropsychological testing does not determine by itself whether someone has epilepsy.

Read more: Memory & Cognition →

PET, SPECT and other advanced tests

MRI Post-Processing and Morphometric Analysis →

FDG-PET in Epilepsy →
Ictal and Interictal SPECT →
MEG and Magnetic Source Imaging →
EEG Source Imaging →
Functional MRI for Language and Motor Mapping →
7-Tesla MRI in Epilepsy →

PET and SPECT are not routine first-line tests for diagnosing epilepsy. They are mainly used in specialist centres when more detailed localisation is needed, particularly in people with drug-resistant focal epilepsy being assessed for surgery.

PET can show patterns of brain metabolism that may help identify an abnormal region between seizures. SPECT assesses cerebral blood flow; when performed during or close to a seizure, it may help identify the region where seizure activity began. Advanced centres may also use functional MRI, EEG source imaging, magnetoencephalography or invasive intracranial EEG in selected cases.

These tests answer specific specialist questions. They are not a hierarchy where everyone with epilepsy progresses through every test.

When presurgical investigation becomes relevant

For people with drug-resistant epilepsy, especially when seizures may arise from one brain region, the diagnostic process can become much more detailed. The aim is to establish as confidently as possible where seizures begin and how that area relates to essential functions such as memory, language, movement and vision.

Presurgical assessment may combine prolonged video-EEG telemetry, epilepsy-protocol MRI, neuropsychology and selected advanced imaging. Some people also require invasive EEG monitoring. Not everyone who undergoes presurgical assessment will proceed to surgery; the assessment itself is used to judge whether surgery is possible and whether the expected benefits outweigh the risks.

Why diagnosis can remain uncertain

Epilepsy is an intermittent disorder. A person may have completely normal neurological examinations, normal blood tests, a normal MRI and several normal EEGs between seizures and still have epilepsy. Conversely, not every blackout, collapse, twitch or episode of altered awareness is epileptic.

That is why diagnosis is a process of combining evidence: the clinical history, eyewitness or video information, examination, EEG, imaging and other targeted investigations. Sometimes the diagnosis becomes clearer only after repeated events, prolonged monitoring or review in a specialist epilepsy service.

The central point

Tests support the diagnosis; they do not replace clinical judgement. A normal routine EEG cannot exclude epilepsy, a normal MRI cannot exclude epilepsy, and an abnormal test does not automatically explain every event a person experiences. The strongest diagnosis comes from fitting the test results to the person’s actual seizure history.

Where next?

Learn about seizure types →
Read about treatment options →
Drug-Resistant Epilepsy →
Genetics & Epilepsy →
Back to Understanding Epilepsy →

Related diagnostic pages

First Seizure: What Happens Next? · Acute Symptomatic and Provoked Seizures · Syncope or Seizure? · EEG Explained Properly · MRI and Neuroimaging in Epilepsy

Conditions that can resemble seizures

Movement Disorders That Can Resemble Epileptic Seizures →
Parasomnias and Nocturnal Seizures — How Specialists Tell Them Apart →
Transient Epileptic Amnesia and Transient Global Amnesia →
Panic Attacks and Focal Seizures — Where the Symptoms Overlap →
Dissociation and Focal Impaired-Awareness Seizures →
When Antiseizure Medicine Side Effects Look Like New Seizures →

Sources

Medical note: This page is for education and awareness and is not a substitute for individual medical advice. Diagnostic pathways vary according to age, clinical circumstances and healthcare system.

Related researched deep dives

Diagnostic traps and seizure mimics

Preparing for your appointment

If you are newly diagnosed, waiting for your first neurology appointment or have questions that have never been answered clearly, use the dedicated appointment guide.

What to Ask at Your Epilepsy Appointment →

Evidence checked: September 2026.