Diagnostic Tests for Epilepsy
A single seizure does not necessarily mean that a person has epilepsy. It does, however, merit further examination and testing to ensure a precise diagnosis. In cases where surgery is recommended, additional tests can help surgeons best prepare for the operation.
There are many types of epilepsy and epilepsy-related syndromes. Other conditions, such as narcolepsy, cardiac syncope, and arrhythmia, mimic some of the symptoms of epilepsy. An excellent tool to help determine a specific diagnosis is the electroencephalogram, or EEG. During this non-invasive test, several electrodes are placed on a patients scalp. They record electrical impulses from the brain known as brain waves. The results of an EEG can be printed out and interpreted by an epileptologist.
Because a non-invasive EEG can only measure electrical activity on the brains surface, sometimes the readings come back normal when, in fact, there is abnormal activity deeper in the brain. In certain cases, the electrodes are implanted surgically through tiny holes in the skull to obtain a more precise reading.
Continuous Video EEG Monitoring
It is helpful for the epileptologist to study the brain waves over time. This can be accomplished through continuous video EEG monitoring, where a patient stays in a special unit for at least 24 hours. Antiepileptic medication is stopped for the duration of this test, as the objective is for seizures to occur so the abnormal brain waves they produce can be recorded.
A video camera connected to the EEG provides constant monitoring, enabling the medical team to pinpoint the area where a seizure occurs and track the patients physiological response to the seizure. Continuous monitoring can also help distinguish between epilepsy and other conditions, characterize the seizure type for more precise medication adjustments, and prior to surgery, locate the originating area of seizures within the brain.
During periods when they are not having a seizure or undergoing neuropsychological testing, patients can have visitors, read, and watch TV.
The Wada Test
When surgeons operate to relieve seizures, they need to know all they can about the structure of the patients brain. The intracateroid sodium ambobarbital, or Wada test, helps to identify the areas of a persons brain that control speech and memory functions. During this pre-operative procedure, an angiogram of the brain is taken (an X-ray of the brains blood vessels). A drug is then injected into the patient that anesthetizes one side of the brain; the patient is asked to respond to a series of memory and speech-related tests. From this test, the neurosurgical team can determine where the areas of the brain that control speech and memory are located, and thus avoid those areas during surgery.
Magnetic Resonance Imaging (MRI) and Functional MRI
This equipment uses a magnetic field rather than radiation to capture an image. By scanning at different angles, it can provide a 3-dimensional image of the brain.
Functional MRI takes images in "real time" sequence and faster than traditional MRI. This technique often is used before surgery to create a map of the brain and indicate where language, motor, and sensory areas are located. During the scan, the patient is asked to perform certain tasks, such as tapping fingers or repeating a list of words. From the image, the neurological team can locate the area of the brain controlling that function.
Single Photon Emission Computed Tomography, or SPECT, is a scanner that measures a low-dose radioactive material as it circulates through the brain. SPECT can track cerebral blood flow and detect alterations in brain metabolism between and during seizures. This information can be useful in locating the seizure focusthe place within the brain where a seizure originates.
Computed Tomography (CT)
By using this combination of a sophisticated X-ray device and a computer, the brains structure and tissues can be imaged. The Center uses a state-of-the-art scanner to produce images with unprecedented speed and image clarity.
A patients cognitive abilities, memory, and motor skills often are assessed through a variety of neuropsychological tests.