Evoked Potentials

Trusted Diagnostics from Great River Sleep Disorders Center

Evoked potential studies are a group of tests of the nervous system that measure electrical signals along the nerve pathways. Nerves carry information through the body by sending electrical signals down the length of the nerve. These signals can be registered by electrodes placed on a patient's skin.

The then patient receives a series of painless stimuli while a computer records the neurological responses. Hundreds of responses are received, amplified and averaged. Neurologists can analyze this information and make conclusions about a patient's nerve pathways, especially those in the spinal cord and brain. This data can also indicate degeneration or disease and can help pinpoint the location of lesions that could be disrupting these pathways.

The most common types are:

• Auditory (BAEP) - A Brainstem Auditory Evoked Potential delivers a series of clicking sounds through a set of headphones while the patient remains relaxed with their eyes closed. With surface electrodes placed on the scalp, waveforms are averaged and plotted on a computer. This test is helpful in evaluating the auditory nerve pathway and can aid in the diagnosis of hearing loss and damage to the acoustic nerve (which carries signals from the ear to the brain stem). Other diagnoses include acoustic neuromas (tumors of the inner ear) and multiple sclerosis (a chronic disease in which nerves lose patches of their outer covering). They may also be used to determine brain death and to monitor brainstem function during surgery.
• Visual (VEP) - A Visual Evoked Potential evaluates the visual pathways and functional status of the optic nerve. With surface electrodes placed on the scalp, patients are asked to stare at different patterns on a monitor while the computer averages responses that represent the function of the optic nerve pathway. Waveforms are plotted out and interpreted by a neurologist. Visual evoked potentials are used to diagnose vision loss due to optic nerve damage. VEP’s are also used to aid in the diagnosis of multiple sclerosis.
• Somatosensory Evoked Potential (SSEP) - Somatosensory evoked potentials record nerve impulse transmissions from the arms and legs to the brain. These studies can be used to diagnose nerve damage within the spinal cord or nerve roots from trauma, multiple sclerosis, or other degenerative conditions. Somatosensory EP's can also help physicians determine whether a patient is suffering from peripheral nerve disease or central nerve disease. A small electrical current is applied to the skin overlying the nerves in the arms and legs that are being tested. The current creates a tingling sensation but is not painful. Waveforms are then averaged and plotted on a computer for a neurologist to interpret.

How should I prepare for Evoked Potential test?

• Avoid using hairspray, gels or oils prior to your appointment and your hair must be dry.
• Take prescribed medications unless your physician gives you other instructions.
• Bring a complete list of all medications you are currently taking.
• Eat a normal diet.

Have more questions about your upcoming EP study? Contact Great River Sleep Disorders Center at (319) 768-4325 today.