Epilepsy is a neurological disorder characterized by recurrent, unprovoked seizures, which are sudden, uncontrolled electrical disturbances in the brain. These episodes can cause changes in behavior, movements, feelings, and consciousness. Diagnosing this condition is a complex process because there is no single test that definitively confirms epilepsy. Instead, doctors rely on a combination of a detailed medical history, physical examinations, and a variety of specialized diagnostic procedures to understand the nature of the seizures and determine an underlying cause.
The Foundational Role of Clinical Assessment
The diagnostic journey begins with a comprehensive clinical assessment, the most informative step in determining if a patient has epilepsy. Doctors take an exhaustive medical history, focusing heavily on the events leading up to, during, and immediately following a suspected seizure. Since patients often cannot recall the episode, witness accounts are especially valuable in describing the seizure’s frequency, duration, and specific symptoms.
This historical information helps establish the stereotypic, or repeated, nature of the events, which is a hallmark of epileptic seizures. A physical and neurological examination is then performed to assess the function of the nervous system. This examination checks mental function, motor skills, sensory function, and reflexes to look for abnormalities that might suggest a brain disorder or a non-epilepsy cause for the episodes, such as a stroke or tumor.
Measuring Electrical Activity with EEG
The Electroencephalogram (EEG) is typically the most common test used to investigate the brain’s electrical activity. Small metal discs, called electrodes, are temporarily attached to the scalp to record the brain’s continuous electrical patterns. This test seeks to identify abnormal patterns, known as epileptiform discharges, which appear as spikes, sharp waves, or spike-and-wave complexes, even when the patient is not actively seizing.
A routine EEG is often short, lasting only about 20 to 40 minutes, but its diagnostic sensitivity for detecting these abnormal discharges is only moderate. A normal EEG, therefore, does not rule out epilepsy, especially if the seizures originate in areas of the brain that are difficult for scalp electrodes to record. To increase the chances of capturing an event, doctors may use activating methods like sleep deprivation, hyperventilation, or photic stimulation.
In cases where routine testing is inconclusive, a prolonged video-EEG may be necessary, often requiring a stay in a specialized epilepsy monitoring unit. This procedure synchronizes electrical recording with a video camera to capture behavioral changes during a seizure, correlating the physical event with the brain’s electrical activity. Recording an actual seizure (an ictal event) provides the most direct proof of epilepsy and helps refine the diagnosis of the seizure type.
Structural and Metabolic Imaging Tests
While the EEG looks at brain function, structural and metabolic imaging tests visualize the brain’s anatomy and chemical processes. The primary tool is Magnetic Resonance Imaging (MRI), which uses magnetic fields and radio waves to create highly detailed images of soft tissues. MRI identifies underlying structural causes of seizures, such as brain injury, tumors, congenital malformations, or evidence of past strokes.
Computed Tomography (CT) scans may also be used, particularly in emergency situations, to quickly check for issues like bleeding or acute injury. For a more advanced view of brain activity, functional imaging tests are sometimes utilized to measure metabolism and blood flow. Positron Emission Tomography (PET) scans, for instance, measure glucose metabolism in the brain, often showing reduced metabolic activity in the area where seizures originate.
Single-Photon Emission Computed Tomography (SPECT) measures cerebral blood flow and can be especially useful when performed during a seizure (ictal SPECT). Comparing a scan taken during a seizure to one taken between seizures (interictal) helps to pinpoint the seizure focus, as the active area typically shows increased blood flow.
Specialized and Differential Diagnostic Tools
Other specialized tests are often needed to complete the diagnostic picture and rule out non-epileptic causes of spells. Blood tests are routinely performed to check for factors that can mimic or trigger seizures, including:
- Severe electrolyte imbalances
- Infections
- Metabolic disorders
- Drug toxicity
These tests ensure that the episodes are not due to temporary, treatable systemic issues rather than a chronic neurological condition.
Genetic testing has become an increasingly important tool, especially for individuals with unexplained epilepsy or cases involving developmental delays. Over 200 genes have been identified that are associated with epilepsy, and testing can involve targeted gene panels or more comprehensive whole-exome sequencing. Identifying a genetic cause can provide a definitive diagnosis and may influence the choice of anti-seizure medication.
The ultimate goal is differential diagnosis, which is the process of distinguishing epilepsy from other conditions that can cause similar symptoms, such as fainting (syncope), migraines, or psychogenic non-epileptic seizures. By integrating the patient’s clinical history, the electrical data from the EEG, the structural information from imaging, and the results from specialized blood and genetic tests, doctors can confidently arrive at a final diagnosis and determine the most appropriate course of treatment.