Epilepsy is a neurological disorder characterized by recurrent, unprovoked seizures. A seizure is a brief episode caused by abnormal, excessive electrical activity in the brain’s nerve cells. No single test definitively diagnoses epilepsy. Diagnosis relies on a comprehensive evaluation that synthesizes clinical observation, patient history, and specialized tests. This systematic approach confirms the events were seizures and rules out other possible causes.
Initial Assessment and Medical History
The diagnostic process begins with a detailed clinical interview. Since providers rarely witness an event, descriptions from the patient and eyewitnesses are the most valuable initial data. The physician requires a minute-by-minute account of what happened before, during, and after the event, including any warning signs or post-event confusion. These descriptions help determine if the episode was an epileptic seizure or a non-epileptic event, such as syncope or a migraine with aura.
The doctor also reviews the patient’s medical background and family history, looking for past head injuries, infections, or a family predisposition to seizures. A physical and neurological examination follows to check for subtle signs of underlying neurological problems. This exam assesses reflexes, motor function, coordination, and mental status to establish a baseline and look for abnormalities suggesting a structural cause.
Electroencephalogram (EEG): The Core Diagnostic Tool
If the initial history suggests a seizure disorder, the electroencephalogram (EEG) is the primary functional test. This non-invasive procedure uses electrodes affixed to the scalp to record the brain’s electrical activity. The electrodes detect synchronized electrical impulses between brain cells, which are displayed as brain waves.
A routine EEG lasts 20 to 40 minutes and often includes activation procedures like deep breathing (hyperventilation) or flashing lights (photic stimulation). These techniques provoke abnormal electrical patterns, called epileptiform discharges or spikes, characteristic of epilepsy. Since brain activity may appear normal between seizures, a routine test is often inconclusive.
Specialized EEG Procedures
Specialized procedures increase the chance of capturing intermittent discharges. A sleep-deprived EEG requires the patient to stay awake the night before, as fatigue can increase the likelihood of abnormal activity. Video-EEG monitoring, considered the gold standard, involves continuous monitoring by both EEG and video during a hospital stay. This allows specialists to correlate the patient’s physical behavior with corresponding electrical patterns, confirming if the episode was an epileptic seizure. A normal EEG does not rule out epilepsy, nor does an abnormal EEG always confirm it, making clinical judgment essential.
Structural and Metabolic Rule-Outs
Testing also rules out other conditions that cause seizures but are not epilepsy. Structural imaging visualizes the brain’s physical anatomy, most often using Magnetic Resonance Imaging (MRI). MRI provides highly detailed, three-dimensional images, superior to a standard Computed Tomography (CT) scan for this purpose.
The MRI checks for structural abnormalities causing seizures, such as brain tumors, evidence of stroke, traumatic injury, or cortical malformations. Identifying a structural lesion provides a likely cause, which affects treatment planning. If MRI is unavailable, a CT scan may be used, though it offers less detail regarding soft tissue structures.
Blood tests and lab work exclude metabolic or systemic causes of seizure-like events. These tests check for electrolyte imbalances (e.g., low sodium or calcium), low blood sugar (hypoglycemia), infection, or organ failure. They also detect the presence of drugs or alcohol that might provoke a seizure. In rare cases, a lumbar puncture may analyze cerebrospinal fluid for signs of infection or inflammation.
Confirming the Diagnosis
The final diagnosis of epilepsy is a clinical determination, requiring the doctor to synthesize all gathered evidence rather than relying on a single test result. The International League Against Epilepsy (ILAE) provides the accepted clinical criteria, which generally require experiencing at least two unprovoked seizures occurring more than 24 hours apart.
Diagnosis can also be made after a single unprovoked seizure if imaging or EEG results indicate a high probability of recurrence. The physician must perform a differential diagnosis, systematically ruling out conditions that mimic seizures, such as heart rhythm disturbances (syncope), panic attacks, or sleep disorders.