Diagnosing Epilepsy

By Wendi Hope Bishop, Editor  

The key to diagnosing epileptic seizure is electroencephalography (EEG) or "brain wave" recording. This is a recording of the electrical activity generated naturally by the brain, typically recorded by placing small metal disks on the scalp. 

Epilepsy is characterized by the occurrence of two or more seizures. Epileptic seizures usually, but not always, associated with loss of awareness or loss of consciousness.  Epileptic seizures are associated with convulsions in some cases. There are other non-epileptic causes of loss of consciousness such as syncope or fainting.

The diagnosis of epilepsy is dependant on the ability to clearly diagnose that the recurrent spells are epileptic seizures. People with epileptic seizures have three phases to their condition. The ictus is the active seizure process, the post-ictal period typically is a period of confusion lasting several minutes afterward and the inter-ictal period is the time between seizures.

The key to diagnosing epileptic seizure is electroencephalography (EEG) or "brain wave" recording. This is a recording of the electrical activity generated naturally by the brain, typically recorded by placing small metal disks on the scalp. The resulting recording is a graph that looks like a set of several wavy lines. Clinical EEG has been available since 1930, and is recorded digitally on a computer. 

The waves, or waveforms as they actually are called, have shapes and appearances that are associated with specific characteristics of brain function and consciousness level. Wake and sleep periods appear very differently. The EEG characteristic of seizure activity is the occurrence of waveforms known as spikes and sharps that appear as very sharp or dagger-like shapes on the recording. Spikes can occur either while the patient is having the seizure or between seizures. 

There are many different classifications of seizures. Basically, seizures can be divided into two groups: Primary generalized seizures and focal seizures with or without generalization.

Primary generalized seizures are associated with spikes that are deep in the brain and are not associated with tumors, strokes or other types of anatomical lesions. These generalized seizures often are associated with convulsions. 

Focal seizures arise in the outer layer of the brain known as the cortex, and in some cases can spread to the whole brain from the original small focal spot. Focal seizures can be caused by localized lesions that are irritants to the brain such as strokes or tumors, or may be caused by a congenital structural abnormality. In evaluating patients with seizures, imaging studies of the brain such as computerized tomography (CT) or magnetic resonance imaging (MRI) can be very important to establish a specific cause. Probably 70 percent of patients with seizures will have normal imaging studies. EEG on the other hand, establishes that the 'spell(s),' are epileptic seizure, by recording the abnormal electrical functions of the brain. At best, EEG abnormalities are detected 50 percent of the time and seldom are seizures actually "captured" during an EEG recording. Techniques are employed to enhance the chance of detecting epileptogenic activity such as sleep deprived EEG. Fatigue and lack of sleep are stressful for the brain and tend to increase the likelihood that abnormalities might be found.

To further improve the likelihood of recording seizure activity (spikes, etc.), and visualize actual seizures, a long-term recording approach is widely used, including here at UT Knoxville. This technique is video with EEG monitoring in an epilepsy monitoring unit (EMU).  The patient is admitted to the hospital, electrodes are attached to the patients scalp and the recording begins. The recording is constant during the patient's stay, so if seizure activity such as inter-ictal spikes or a seizure event occurs the brain waves are recorded as well as a picture on video. On occasion, the patient's anti-epileptic drugs (AED) are discontinued to increase the likelihood of detecting abnormalities. This must be done very carefully, since seizures carry with them significant risk to the patient.

Use of the Long-Term EEG with video monitoring study substantially increases the likelihood of capturing abnormalities or a seizure event on the recording. Recording such EEG seizure activity allows the physician to determine the seizure type and the location of the EEG abnormality (such as spikes), which allows the physician to make the best choice of seizure drugs. On some occasions, it helps establish the potential usefulness of surgery to remove the epileptogenic (seizure) focus.

Capturing an actual seizure, in addition to the capture of abnormal waveforms, enables the clarification of the seizure and correlates it well with the abnormal electrical discharge from the brain. Recording a seizure that is atypical and is not associated with EEG abnormalities enables the physician to diagnose seizure of non-epileptic nature, which usually is related to non-physical factors. This is a very important distinction requiring and enabling a much different approach to prescriptions and treatments.

EMU and video-EEG monitoring provides important, often essential information for the diagnosis and treatment of epilepsy. Equally important, it helps differentiate other types of problems that are treated in a variety of ways.

6/28/2005