Epilepsy is a brain disease defined by recurring, unprovoked seizures. More than 50 million people worldwide live with it, and nearly 80% of them are in low- and middle-income countries. A diagnosis typically requires at least two unprovoked seizures occurring more than 24 hours apart, though in some cases a single seizure is enough if the risk of another one is high.
What Happens in the Brain During a Seizure
Your brain runs on a constant balancing act between signals that excite nerve cells and signals that calm them down. In epilepsy, that balance tips toward excitation. Groups of neurons begin firing in abnormal, synchronized bursts, producing the electrical storm we call a seizure. This can happen because the calming signals are too weak, the excitatory signals are too strong, or both. The location and spread of that abnormal activity determines what the seizure looks like from the outside, whether it’s a brief staring spell, a strange sensation, or full-body convulsions.
Types of Seizures
Seizures fall into a few broad categories based on where the abnormal electrical activity starts. Focal seizures begin in one specific area of the brain. Depending on which area is involved, you might experience unusual movements on one side of the body, sudden emotions like fear, or sensory changes like strange tastes or smells. You may or may not lose awareness during a focal seizure.
Generalized seizures involve both sides of the brain from the start. These include tonic-clonic seizures (the type most people picture, with stiffening and rhythmic jerking), absence seizures (brief staring episodes common in children), and several other subtypes. A third category, called unknown onset, applies when no one witnessed the beginning of the seizure or the information is incomplete. The International League Against Epilepsy maintains a formal classification system that currently includes 21 distinct seizure types.
What It Takes to Get a Diagnosis
The formal diagnostic criteria, established by the International League Against Epilepsy, include three pathways to a diagnosis. The most common is having at least two unprovoked seizures more than 24 hours apart. But you can also be diagnosed after a single unprovoked seizure if your doctor determines you have at least a 60% chance of having another seizure within the next 10 years. The third pathway is meeting the criteria for a recognized epilepsy syndrome, which is a specific pattern of seizure type, age of onset, and EEG findings that doctors can identify as a known condition.
The word “unprovoked” is critical here. A seizure caused by an obvious trigger, like extremely low blood sugar, a severe electrolyte imbalance, a high fever in a young child, or drug withdrawal, doesn’t count toward an epilepsy diagnosis. Those are called provoked seizures, and they can happen to anyone under the right circumstances. The diagnostic process always involves ruling out these reversible causes first.
Blood Tests and Ruling Out Other Causes
After a first seizure, doctors order blood work to check for metabolic problems that could have triggered it. This typically includes blood sugar, electrolytes like sodium and calcium, and sometimes ammonia and lactate levels. Blood gases may be checked to look for acid-base imbalances. If infection is suspected, spinal fluid may be tested. Toxicology screening can identify drugs or substances that lower the seizure threshold. The goal is to make sure the seizure wasn’t a one-time event caused by something fixable.
How EEG Works in Diagnosis
An electroencephalogram (EEG) is the central tool for diagnosing epilepsy. It records the brain’s electrical activity through sensors placed on the scalp and looks for abnormal patterns that indicate seizure-prone tissue. Even between seizures, the brain of someone with epilepsy often produces characteristic bursts of activity called interictal epileptiform discharges. These show up on the EEG as spikes, sharp waves, or spike-and-wave complexes, each lasting fractions of a second.
Different patterns point to different types of epilepsy. A rhythmic 3 to 4 Hz spike-and-wave pattern is the hallmark of childhood absence epilepsy. Slower spike-and-wave discharges, around 1 to 2.5 Hz, are associated with Lennox-Gastaut syndrome, a severe form of childhood epilepsy. Spikes centered over the sides of the head (called centrotemporal or Rolandic spikes) point to a common and relatively benign childhood epilepsy that most children outgrow.
A standard EEG lasts about 20 to 40 minutes and may not catch anything abnormal, especially if your seizures are infrequent. When results are inconclusive, doctors may recommend inpatient video-EEG monitoring, which is considered the gold standard for distinguishing epileptic seizures from non-epileptic events. You stay in a monitoring unit with both EEG and video recording running continuously. Research suggests that 24 hours of monitoring is sufficient for most people, though extending to 72 hours increases the chances of catching abnormal activity, particularly in focal epilepsy.
Brain Imaging With MRI
Most people being evaluated for epilepsy will get a brain MRI. High-resolution imaging can reveal structural problems that cause seizures, including areas of abnormal brain development (focal cortical dysplasia), scarring in the memory centers of the brain (hippocampal sclerosis), tumors, cysts, or evidence of prior strokes or injuries. In one study of patients with generalized epilepsy, 24% had MRI abnormalities, though the majority of those were nonspecific findings. When MRI does reveal a clear structural abnormality, its location often lines up with where the EEG shows abnormal electrical activity, which helps confirm the diagnosis and may guide treatment decisions.
When Genetic Testing Is Used
Genetic testing isn’t part of a routine epilepsy workup, but it plays an important role when epilepsy appears alongside developmental delays, autism spectrum disorder, or unusual physical features. In these cases, doctors typically follow a stepwise approach. The first step is a chromosomal microarray, which looks for missing or extra segments of DNA. If that comes back normal, an epilepsy gene panel is the next step. These commercially available panels test anywhere from 70 to 465 genes known to be involved in epilepsy. If both are negative, whole-exome sequencing, which reads nearly all protein-coding genes, may be considered. Identifying a genetic cause can sometimes change treatment, because certain gene variants respond better to specific therapies.
Telling Epilepsy Apart From Non-Epileptic Events
Not every episode that looks like a seizure is one. Fainting spells, heart rhythm problems, sleep disorders, and psychogenic non-epileptic seizures (PNES) can all mimic epilepsy. PNES are episodes that resemble seizures but are not caused by abnormal electrical activity in the brain. They are more common in women and tend to start around age 25 on average, somewhat later than most forms of epilepsy.
Several clinical clues help distinguish the two. PNES episodes typically start gradually, while epileptic seizures begin abruptly. Side-to-side head shaking occurs in about 36% of PNES cases but only 8% of epileptic seizures. The movements in PNES tend to be more violent and high-amplitude, while epileptic seizure movements are usually more rhythmic and slower in frequency. People with PNES are also more likely to report prolonged warning symptoms lasting hours or even days before an episode, whereas epileptic auras are brief and occur immediately before the seizure. Video-EEG monitoring is the definitive way to settle the question: if an episode occurs while the EEG shows normal brain activity, it’s not an epileptic seizure.
Getting the distinction right matters enormously. People misdiagnosed with epilepsy may take seizure medications for years without benefit, while the underlying cause of their episodes goes untreated.