Understanding epilepsy
A first suspected seizure is the beginning of an investigation, not automatically a diagnosis of epilepsy. The aim is to work out what happened, whether there was an acute cause, whether the event was epileptic, and how likely another seizure may be.
Central point: One seizure can be serious and deserves proper assessment, but one seizure does not automatically equal epilepsy.
What should happen after a first suspected seizure?
NICE recommends urgent referral for specialist assessment after a first suspected seizure, with an appointment within 2 weeks. The specialist assessment is not simply about confirming epilepsy. It is also about actively considering other explanations.
The history is one of the most important tests
The description of what happened before, during and after the event can be more informative than any single scan or laboratory test. Clinicians may ask about posture, warning symptoms, colour change, eye position, stiffening, jerking, head turning, automatisms, speech, responsiveness, tongue injury, incontinence, duration, recovery, confusion and weakness afterwards.
Witness accounts and safely recorded smartphone video can add useful information because the person may have limited or no memory of the event. They do not diagnose epilepsy by themselves, but they can improve the quality of specialist assessment.
Why an ECG matters
NICE recommends a 12-lead electrocardiogram (ECG) in the assessment of a first suspected seizure because some cardiac causes of transient loss of consciousness can resemble epilepsy. Arrhythmias and inherited cardiac conditions can be important alternative diagnoses, particularly when collapse occurs during exertion, there is unexplained breathlessness, an abnormal ECG or a family history of sudden cardiac death at a young age.
Blood tests and acute causes
Assessment may include tests for metabolic or systemic causes when clinically appropriate. Severe hypoglycaemia, electrolyte disturbances, intoxication, withdrawal, infection and acute brain injury can provoke seizures. A seizure closely linked to an acute insult is classified differently from an unprovoked seizure and does not automatically establish epilepsy.
EEG after a first seizure
If the history and examination suggest an epileptic seizure, NICE recommends considering EEG to support diagnosis and help classify seizure type or epilepsy syndrome. If EEG is requested after a first seizure, NICE says it should be performed as soon as possible, ideally within 72 hours.
A normal routine EEG does not exclude epilepsy. Routine interictal EEG has limited sensitivity because epileptiform activity may not appear during a short recording. If routine EEG is normal and uncertainty remains, sleep-deprived EEG and then ambulatory EEG may be considered. A positive epileptiform EEG finding can strengthen the diagnosis and may also affect estimated recurrence risk.
When is brain imaging used?
Neuroimaging is used to look for structural causes when these are suspected. MRI is generally the preferred detailed imaging test for epilepsy assessment, although urgent CT may be used in emergency settings when acute pathology such as bleeding, major trauma or another time-critical problem is suspected.
Does one unprovoked seizure mean epilepsy?
Not necessarily. Under the ILAE operational definition, epilepsy can be diagnosed after at least two unprovoked or reflex seizures more than 24 hours apart. It can also be diagnosed after one unprovoked or reflex seizure when the probability of another seizure is judged to be at least 60% over the next 10 years, or when an epilepsy syndrome is diagnosed.
This is why clinicians do not use a single universal recurrence percentage. Risk is individual. Factors associated with a higher recurrence risk include epileptiform EEG abnormalities, a relevant structural brain abnormality, a previous brain insult and, in adults, a first seizure occurring during sleep. Older evidence-based guidance estimated overall adult recurrence risk after a first unprovoked seizure at roughly 21% to 45% within the first 2 years, but an individual’s risk can be meaningfully lower or higher than that range.
Will antiseizure medication be started immediately?
Not always. The decision depends on whether the event was unprovoked, the likelihood of recurrence, EEG and imaging findings, the suspected cause, the person’s circumstances and the balance between reducing near-term recurrence and potential medication adverse effects. Immediate treatment after a first unprovoked seizure can reduce short-term recurrence, but that does not mean every person should begin long-term treatment after one event.
Safety while the diagnosis is being worked out
Until the cause is clearer, practical safety matters. Advice may include avoiding unsupervised swimming, taking care around heights, open flames and machinery, and following local driving rules. In the UK, a first seizure or suspected seizure can have driving implications and should be discussed with the appropriate clinician and the DVLA rules checked directly.
When urgent medical help matters
Emergency assessment is particularly important when a seizure is prolonged, repeats without recovery, occurs with significant injury, persistent breathing difficulty, pregnancy, suspected poisoning or severe metabolic disturbance, meningitis or encephalitis features, or when the person does not return towards their usual level of consciousness. A first seizure with an acute neurological deficit or other signs of a serious underlying cause also needs urgent evaluation.
Related pages
Diagnosis and Tests · Causes of Epilepsy · Seizure Types · When to Call Emergency Services
Preparing for your first epilepsy appointment
If you are waiting for neurology after a first seizure or recent diagnosis, take a written list of questions with you rather than relying on memory in the appointment.
What to Ask at Your Epilepsy Appointment →
Sources
NICE NG217 — Diagnosis and assessment of epilepsy
ILAE — Operational definition of epilepsy
This page provides general educational information and is not individual medical advice. A first suspected seizure should be assessed by an appropriate healthcare professional.