Epileptiform activity is the term for brief, sharp bursts on an EEG that resemble the brain patterns seen in epilepsy, usually recorded while no seizure is happening. It signals that the brain may have a tendency toward seizures, and doctors use it to judge whether seizures are likely to come back.1PubMed. Electroencephalography after a single unprovoked seizure But it is a clue, not a verdict. On its own it neither confirms nor rules out epilepsy, so doctors always read it alongside what actually happened to you.
What Spikes and Sharp Waves Look Like on the Recording
An EEG draws the brain’s electrical activity as wavy lines, and normal rhythms rise and fall smoothly. Epileptiform discharges are different. They show up as sudden pointed spikes, or slightly broader sharp waves, that jump out from that background. A spike is often followed by a slower wave, which your report may call spike-and-wave, and the doctor counts how many appear and how typical their shape is.2aesnet.org. Relationship-between-Interictal-Spikes-and-Ictal-Onset-Zone-on-Subdural-EEG-Recordings One very typical spike can be enough for a confident reading, while less distinct ones need to appear several times before an expert calls the EEG abnormal.3PubMed Central. Spike count and morphology in the classification of epileptiform discharges
Each spike reflects a large group of nerve cells firing at once in an unusually strong electrical surge.4PubMed Central. The Paroxysmal Depolarization Shift: Reconsidering Its Role in Epilepsy, Epileptogenesis and Beyond The electrodes sit on the scalp and pick up the combined activity of many cells beneath them, so the tracing is a blurred summary rather than a picture of single nerve cells.5PubMed Central. Of the Mechanisms of Paroxysmal Depolarization Shifts: Generation and Maintenance of Bicuculline-Induced Paroxysmal Activity in Rat Hippocampal Cell Cultures Doctors read spikes by comparing electrodes against each other, looking for where the peak is tallest. The recording usually includes rest with eyes closed, eyes open, and often a flashing light and deep breathing, which can bring out spikes that rest alone does not.
Your report may say “interictal.” That simply means the spikes were recorded between seizures, not during one. Spikes are split-second events, usually with no symptom you would notice. A seizure on EEG looks different: a sustained, evolving rhythm lasting seconds to minutes.
Reports usually have a description section and an “impression” section that summarizes the conclusion. Phrases like “epileptiform discharges” or “sharp waves” mean the reader saw seizure-type spikes. “Focal” or the name of a brain area means they came from one region, while “generalized” means both sides at once. “Non-specific” or “sharp transients” usually means something unusual but not clearly epileptiform.
An EEG can be called abnormal because the background is slow or uneven, which is a different finding. Slowing can come from drowsiness, medicines, or a past head injury, and it does not by itself point to epilepsy. Check whether your report names spikes or sharp waves specifically, since that is the wording that matters for seizure risk.
Does Epileptiform Activity Mean You Have Epilepsy
Not by itself, but it does shift the odds. Across many studies after a first unprovoked seizure, about 6 in 10 people with spikes on their EEG had another seizure.6PubMed Central. Presence of interictal epileptiform EEG discharges implies increased risk of recurrence after the first unprovoked seizure: Report of the International League Against Epilepsy and International Federation of Clinical Neurophysiology About 4 in 10 people without spikes also had one.7PubMed Central. Presence of interictal epileptiform EEG discharges implies increased risk of recurrence after the first unprovoked seizure: Report of the International League Against Epilepsy and International Federation of Clinical Neurophysiology So in these studies, spikes went with roughly 20 percentage points of extra risk, a real difference but not certainty.8PubMed Central. Presence of interictal epileptiform EEG discharges implies increased risk of recurrence after the first unprovoked seizure: Report of the International League Against Epilepsy and International Federation of Clinical Neurophysiology
Those percentages come from groups of people, so they describe how things tend to go across many people and cannot say what will happen to you. They apply to people who have had a first unprovoked seizure, and they mean less for someone tested for fainting or headaches.
The diagnosis matters because epilepsy is generally diagnosed when someone has had one seizure plus a high chance of more. Doctors often call the chance high when it is around 60 percent or more over the next ten years, and spikes help them reach that judgment. That lets a doctor diagnose epilepsy after just one seizure, without waiting for a second. Spikes after a first seizure can make the diagnosis possible and open a discussion about whether to begin a daily medicine or watch and wait.9PubMed. Electroencephalography after a single unprovoked seizure Even so, the diagnosis still rests on what the seizure looked like, not the EEG alone.
Several things are weighed alongside the tracing. A clear description of the event from a witness often matters most. Brain imaging can show a cause such as scarring or a past injury. Whether the seizure had a trigger, like alcohol withdrawal or low blood sugar, changes its meaning. Age and family history feed into the decision too.
Why a Normal EEG Doesn’t Rule Epilepsy Out
A routine EEG catches only a small window of time. In one adult study, a routine EEG showed spikes in only about 1 in 5 people who later had another seizure.10PubMed. Diagnostic value of EEG after a first unprovoked seizure in adults – A population-based study When spikes did appear, they were almost never seen in people who stayed seizure-free.11PubMed. Diagnostic value of EEG after a first unprovoked seizure in adults – A population-based study So a positive result is very telling, while a normal result reassures much less, since spikes come and go and a 20 to 40 minute recording may miss them.
Longer recordings find more. After a first seizure, a sleep-deprived EEG picked up spikes in about 45% of people who had them, and a longer at-home recording in about 63%.12PubMed. Detecting interictal discharges in first seizure patients: ambulatory EEG or EEG after sleep deprivation? In another study, though, sleep deprivation did not clearly beat a routine EEG, so the evidence is mixed.13PubMed. Yield of Sleep Deprivation EEG in Suspected Epilepsy. A Retrospective Study
For a sleep-deprived EEG, you stay up most or all of the night before, so arrange a ride home. An ambulatory EEG keeps electrodes on your head for a day or more at home, and you keep a diary of any events so doctors can match them to the tracing. For either test, wash your hair beforehand and skip hair products so the electrodes stick well.
A repeat is most worthwhile when the story strongly suggests seizures but the first tracing was normal. Recording sleep matters because drowsiness and light sleep often bring out spikes that waking tracings hide.
A normal result leaves the diagnosis resting on the description of the event, which is why witnesses and phone videos carry so much weight. It is more reassuring when the event story also sounds like fainting or another non-seizure cause. And some seizures start deep in the brain where scalp electrodes pick up little, so even a seizure itself can sometimes leave no mark on the scalp tracing.
When Normal Patterns Are Mistaken for Epileptiform Activity
Some normal brain patterns, called benign variants, look spiky but have nothing to do with epilepsy.14PubMed. Benign epileptiform variants in EEG: A comprehensive study of 3000 patients Examples include wicket spikes, small sharp spikes, and a rhythmic pattern of drowsiness, all often overread as epileptiform.15PubMed. Normal Variants Are Commonly Overread as Interictal Epileptiform Abnormalities Misreading them can delay the right diagnosis for fainting, panic attacks, or non-epileptic seizures.16PubMed. Normal Variants Are Commonly Overread as Interictal Epileptiform Abnormalities A rare adult pattern, which a report may abbreviate as SREDA, can resemble a seizure but is harmless.17PubMed. Subclinical rhythmic electrographic discharges of adults (SREDA) revisited: a study using digital EEG analysis
Artifacts are signals the EEG records that come from outside the brain, such as blinking, muscle tension, heartbeat, sweat, or phones.18Epileptic Disorders. Normal variants and artifacts: Importance in EEG interpretation A loose electrode can create a sudden tall “pop” at one spot that looks like a focal spike.19Integris Health. Artifacts in EEG: How to Recognize and Reduce Common Recording Pitfalls Experts check whether a spike spreads across nearby electrodes the way real brain activity does.20Bitbrain. EEG Artifacts Types Detection and Removal Techniques Bitbrain
Other clues help too. Real spikes tend to disturb the background around them and often come with a following slow wave, while many normal patterns do not. Normal look-alikes tend to appear in particular states, such as drowsiness, and in particular places on the head. Reading these takes training and experience, which is why a specialist’s reading can differ from a general one.
A second opinion makes sense if medicine was started on the EEG alone and your events don’t sound like seizures, or if seizure medicines haven’t helped at all. Ask whether an epilepsy specialist can review the original tracing, not just the report. A video EEG recorded during a typical event can often settle the question.
Where the Spikes Come From and Why It Matters
Focal spikes most often come from the temporal, frontal, occipital, central, or midline areas.21PubMed. Epileptiform electroencephalographic patterns The location helps doctors guess where seizures start and what they might look like. Temporal spikes are often linked with seizures that begin with a rising feeling in the stomach, a sense of familiarity, or staring and lip smacking. Frontal spikes can go with brief, sometimes bizarre-looking seizures that often happen in sleep. Occipital spikes may go with visual symptoms such as flashing lights or spots. In some children, though, the area with the most spikes is not where seizures begin.22PubMed Central. Interictal EEG spikes identify the region of seizure onset in some, but not all pediatric epilepsy patients
Generalized spike-and-wave, often about three per second, is the classic pattern of absence seizures, driven by loops between deep and outer parts of the brain.23PubMed Central. A brief history on the oscillating roles of thalamus and cortex in absence seizures In life, an absence seizure is a few seconds of blank staring with no response, after which the person carries on as if nothing happened. Hyperventilating in the EEG lab is often used because it can bring out the pattern in a child with absence seizures.
Location also guides treatment. Some medicines work better for generalized epilepsies than focal ones. Focal spikes may prompt an MRI to look for a cause in that area. If medicines fail, the location helps decide whether surgery is an option.
Epileptiform Activity in Babies and in Older Adults
Hypsarrhythmia is a very disorganized, high-voltage pattern of spikes and slow waves with no normal rhythm.24PubMed Central. Electroclinical Features of Infantile Epileptic Spasms Syndrome It is the hallmark of infantile spasms, sudden clusters of brief jerks or stiffening.25Practical Neurology. Epilepsy Essentials: Infantile Spasms—The Biggest Little Seizures A baby with this result needs prompt treatment from a pediatric neurologist.
At home, the spasms look like sudden bending forward or arms flinging out, often in clusters on waking. They are easy to mistake for colic or a startle reflex, so filming an episode on your phone to show the doctor helps. Infantile spasms usually begin in the first year of life, most often in the middle months. The sooner treatment starts, the better the chance of protecting the baby’s development. Treatment is usually started under specialist care with medicines chosen for this condition, and the EEG is repeated to see if the chaotic infant pattern clears.
The chaotic infant pattern points to a seizure type, but it does not on its own say what caused it. Doctors usually go on to look for a cause with imaging, blood tests, and sometimes genetic testing. The cause often shapes the outlook more than the EEG does.
In older adults, spikes without any obvious seizure appeared in about half of people with Alzheimer’s on long recordings, versus a quarter of healthy older adults.26PubMed. Subclinical epileptiform activity accelerates the progression of Alzheimer’s disease: A long-term EEG study Those with spikes lost thinking skills about 1.5 times faster.27PubMed. Subclinical epileptiform activity accelerates the progression of Alzheimer’s disease: A long-term EEG study Some healthy older people also showed spikes, so the finding alone isn’t alarming.28PubMed. Detection of subclinical epileptiform discharges in Alzheimer’s disease using long-term outpatient EEG monitoring
Epileptiform Patterns Seen in the Hospital
In critically ill patients, regular repeating discharges can lie anywhere between clearly harmless and clearly seizure.29Acta Epileptologica. Ictal-interictal continuum: a review of recent advancements Patterns slower than once a second are usually treated as between-seizure, while faster than 2.5 per second with changing rhythm counts as an ongoing seizure.30Acta Epileptologica. Ictal-interictal continuum: a review of recent advancements Faster patterns, and ones that change shape or spread over time, worry doctors more than slow, steady ones. Patterns in the middle zone are judged along with the patient’s condition, other test results, and response to treatment. In patients with repeating discharges on one side, about half had seizures detected.31PubMed. Electrographic Features of Lateralized Periodic Discharges Stratify Risk in the Interictal-Ictal Continuum In liver or kidney failure, triphasic waves can mimic seizures and tend to increase when the patient is stimulated.32The Canadian Journal of Neurological Sciences. Triphasic Waves Versus Nonconvulsive Status Epilepticus: EEG Distinction
EEG monitoring is used in intensive care because seizures in very ill or unresponsive patients can show no visible movements, so the EEG may be the only way to detect them. Continuous recording lets the team watch for patterns to start, speed up, or fade, which is why it may be left running for long periods rather than done as a brief test. Doctors may give a trial dose of seizure medicine to see if the pattern fades, and treating the underlying illness often improves the EEG.
How Medicines Change What the EEG Shows
Fast-acting drugs given in hospital, like benzodiazepines, can quickly suppress spikes.33PubMed. Antiepileptic drugs and the electroencephalogram In people taking levetiracetam, spikes rose when the dose was lowered, showing the drug kept them down.34PubMed Central. Effect of Anti-Seizure Medications on Interictal Epileptiform Discharges in Focal Epilepsy Many seizure medicines also slow the background rhythm, which can make an EEG look worse even as seizures improve.35PubMed. Antiepileptic drugs and the electroencephalogram And some psychiatric medicines, and even some seizure medicines, can make seizures more likely.36PubMed Central. Iatrogenic Epileptogenicity Caused by CNS Drugs: A Short Case Series and Narrative Review
A reader who knows the medicine list can interpret slowing correctly, which is why the list should reach whoever reads the tracing. Bring a full list to the test, and don’t stop seizure medicine before an EEG unless your doctor tells you to. Ask whether a recent dose change could affect the result.
Doctors judge treatment mainly by seizure count, not spike count. Spikes may persist even when seizures are controlled, and repeat EEGs are used for specific questions, such as whether to stop medicine.