NEURO-DIAGNOSTIC CENTER

 Evoked Potential Studies (EP)

An EP is a recording of electrical activity of the brain, spinal nerves, or sensory receptors which occurs in direct response to external stimuli. EPs form a series of waves that require computer averaging to visualize. There are three types of evoked potentials-Auditory, Visual, and Somatosensory. Depending on the clinical symptoms, patients may undergo one or more EP procedures.

Physicians use EPs to reveal abnormalities in patients with suspected multiple sclerosis, optic neuritis, brain stem disorders, or spinal cord disease; they are useful in the evaluation of hearing or vision in patients who cannot cooperate with traditional testing; they are used to monitor the integrity of the nervous system during surgical procedures involving the brain or spinal cord.

Evoked potential testing requires approximately 1 to 3 hours. The SSEP usually requires the most time. A technologist locates sites on the patient's head, arms, legs, or spine and marks the locations for each electrode. Each location is prepped with a special solution. The tech attaches the electrodes to the patient's skin with paste that is water soluble and/or with sticky pad electrodes. The electrodes are checked for adequate connection.

The patient is quiet with eyes closed while the tech collects the AEP and SSEP data. The patient receives stimuli for the AEP from headphones that deliver click sounds to one ear while the other receives static noise. Brief electrical pulses causing slight muscle twitching in the thumb or foot are delivered to patients for SSEP testing. The patient is awake for VEP testing and focusing on a TV screen that is generating a black and white checkerboard pattern. When testing is finished, the tech removes the electrodes and paste residue. EP studies are not painful, though at times may be uncomfortable, they are tolerable, and do not cause after-effects.

A physician specializing in neurology and EP technology prepares a report and interpretation of the EP recording.

The Auditory Evoked Potential (AEP) assists in the evaluation of the auditory nerve pathway from the ear through the brainstem. It provides physicians with information dealing with hearing integrity as well as brainstem function.

The Visual Evoked Potential (YEP) evaluates the pathway from the retinal receptors in the eye to the occipital cortex of the brain. It is useful in the assessment of the parts of the eye and optic nerve that cannot be visualized during a routine eye exam.

The Somatosensory Evoked Potential (SSEP) assesses pathways from the peripheral nerves in the arms or legs, through the spinal cord, to the brainstem or cerebral cortex. It is useful in localizing lesions in the spinal cord.