Learn how epilepsy is diagnosed using EEG, MRI, and blood tests. Understand the patient journey from the first seizure to a confirmed diagnosis.
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Diagnosis and Imaging
Diagnosing epilepsy requires a systematic approach to rule out other conditions that cause temporary loss of consciousness or confusion. The diagnosis is rarely made on the basis of a single test. Instead, it is a puzzle put together using the patient’s history, witness descriptions, and specialized testing. The first step is determining if the event was truly a seizure.
Once a seizure is confirmed, the doctor tries to classify the type of seizure and the epilepsy syndrome. This distinction is vital because some medications work for focal seizures but make generalized seizures worse. The diagnostic process also aims to find the underlying cause, such as a tumor or genetic defect, which might require a different treatment approach.
The epilepsy examination involves a mix of clinical assessment and technological investigation. In the clinic, the neurologist performs a neurological exam to test behavior, motor abilities, and mental function. This helps determine if there is a problem with the brain and nervous system.
Following the physical exam, the doctor orders diagnostic tests. These tests look at the electrical activity of the brain and the physical structure of the brain. The combination of these two perspectives functional and structural allows for a complete diagnosis.
The examination includes:
During the examination, the doctor acts as a detective. They will ask specific questions about the event: Did you have a warning sign? Were your eyes open? Did you bite your tongue? How did you feel afterward? The answers to these questions help localize where the seizure started.
The doctor will then proceed to order an EEG. This is the most common test used to diagnose epilepsy. In this test, electrodes are attached to the scalp with a paste. These sensors record the electrical activity of the brain. If the patient has epilepsy, it is common to see changes in the normal pattern of brain waves, even when the person is not having a seizure.
The EEG is the gold standard for diagnosing epilepsy. It records the brain’s electrical waves. Patients usually come to the lab and have small metal discs pasted to their scalp. They are asked to lie still, open and close their eyes, breathe deeply and rapidly (hyperventilation), and look at a flashing light. These activities are designed to slightly stress the brain to reveal abnormal discharges.
Sometimes, a routine EEG is normal even in a person with epilepsy. In these cases, a prolonged video EEG monitoring may be needed. The patient stays in the hospital for several days while being recorded on video and EEG. The goal is to capture a seizure as it happens to see exactly where it starts in the brain.
An MRI uses powerful magnets and radio waves to create a detailed view of the brain. It is the preferred imaging method for epilepsy because it provides excellent pictures of the brain’s soft tissue. An MRI can detect structural abnormalities that might be causing the seizures.
Common findings on MRI include:
A CT scan uses X rays to create cross sectional images of the brain. While it shows less detail than an MRI, it is often the first test done in an emergency room when a patient presents with a first seizure. It is very fast and readily available.
The CT scan is primarily used to rule out acute causes that need immediate surgery or intervention, such as bleeding in the brain, large tumors, or skull fractures. If the CT is normal, an MRI is usually ordered later for a more detailed look.
Blood tests do not diagnose epilepsy directly, but they are crucial for ruling out other causes of seizures. Seizures can be caused by low blood sugar, low sodium, kidney failure, or liver problems. Correcting these metabolic imbalances often stops the seizures without the need for epilepsy medication.
Blood tests are also used to check for signs of infection, such as meningitis, which can cause seizures. Additionally, doctors may order genetic testing through a blood sample if a genetic form of epilepsy is suspected.
Neuropsychological testing involves a series of tests designed to assess thinking, memory, and speech skills. This testing is performed by a neuropsychologist. It helps doctors determine which areas of the brain are affected by the seizures.
For example, if a patient has poor memory for words, it suggests the problem is in the left temporal lobe. If they have poor memory for faces, it might be the right temporal lobe. This functional map compliments the structural map from the MRI and the electrical map from the EEG.
In complex cases, especially when surgery is being considered, advanced imaging is used. Functional MRI (fMRI) measures blood flow changes that occur when specific parts of the brain are working. Doctors use this to map where speech and movement are controlled to avoid damaging these areas during surgery.
Positron Emission Tomography (PET) scans involve injecting a small amount of low dose radioactive material. The scan shows active areas of the brain. Seizure focus areas often show low metabolism (activity) between seizures and high metabolism during seizures.
Single photon emission computed tomography (SPECT) is another functional imaging test. It is primarily used when an MRI does not show a clear cause for the seizures. A SPECT scan creates a 3D map of blood flow in the brain during a seizure.
This test requires the patient to be in the hospital. A radioactive tracer is injected exactly when a seizure begins. The tracer locks into the brain cells based on blood flow at that moment. The image shows a “hot spot” where the seizure started, guiding surgeons to the precise location of the problem.
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Diagnosis is based on clinical history, EEG findings, and assessment of seizure recurrence risk. Imaging helps identify underlying causes.
No, EEG supports diagnosis but must be interpreted alongside clinical history and examination.
No, many forms of epilepsy have normal MRI findings, especially generalized epilepsies.
Seizure patterns and EEG findings may evolve over time. Repeat testing improves diagnostic accuracy.
Sometimes, if there is high risk of recurrence supported by EEG or imaging findings.
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