Preparing for a Neurodiagnostic Test

Evoked Potentials or EP Test

Evoked Potentials (EPs) are helpful in evaluating a number of different neurological problems including spinal cord injuries, acoustic neuroma and optic neuritis. The EP records electrical activities from the brain, spinal nerves or sensory receptors in response to specific external stimuli. Small electrodes are applied to the scalp and/or other areas of the body, a series of stimuli are introduced, and a computer records the neurological responses. These responses are plotted on a graph and are interpreted by a neurologist. Common types of EPs:

Auditory: BAEP

This test evaluates the auditory nerve pathways from the ears to the brainstem. Four electrodes will be applied to your scalp using a water-soluble paste. You will be asked to put on a set of earphones, which deliver a set of tones/clicks to each ear while the computer records wave forms through the electrodes. The only requirement is that you remain relaxed and still. The testing usually takes 45 minutes.

Visual: VEP

This test evaluates the visual nerve pathways from the eyes to the visual (occipital) cortex of the brain. Three electrodes are applied to your scalp using a water-soluble paste. The room will be darkened and you will be asked to stare at a video screen with changing patterns while the computer records wave forms through the electrodes. This test usually takes 20 minutes.

Somatosensory: SSEPs

This test assesses pathways from the nerves in arms or legs through the spinal cord to the brainstem and cerebral cortex. A small electrical current is applied to the skin overlying the specific arm/leg nerve. The current creates a slight tingling sensation, but is not painful. Each arm or leg is tested separately. This test usually takes about 45 minutes.

Preparation for the EP Test

Typical length of test: 20-45 minutes, depending on type of test

  • There are no special preparations or contraindications for this type of testing.
  • NSMC provides interpreters for non-English speaking patients; please inform the EMG lab whether you will need the interpreter service or if you will bring your own interpreter. Call 781.477.3882 to request an interpreter. For patients who speak English but may not be able to easily communicate their medical histories, it is advisable that a family member or friend familiar with your medical history accompanies you to the testing.

FOLLOW UP:

Your doctor will receive a report within 4-5 days after testing and will contact you with the results.


Electromyography / Nerve Conduction or EMG/NCS Tests

An EMG measures the muscles electrical activity. A small needle will be placed into the muscle that is being tested. You will be asked to slowly contract the muscle, and the electrical activity you create will be recorded on a highly sensitive machine. An NCS measures the speed of an impulse traveling along a nerve. Two small surface electrodes are placed over a particular nerve. A series of mild electrical impulses will then be given in this area. When stimulated, the patient feels a slight tingling sensation. The time it takes for the impulse to travel from one spot to another will be recorded. A neurologist specializing in neurodiagnostic medicine evaluates the data collected.

Preparation for the EMG/NCS Test

Typical length of test: 30-60 minutes

Please shower or bathe prior to the test (the sensors work best when placed on clean skin).

  • Do not use lotion on hands, arms or legs prior to the test.
  • You may be asked to change into a Johnny in the lab depending on which muscles / nerves are being tested. NSMC provides interpreters for non-English speaking patients; please inform the EMG lab whether you will need the interpreter service or if you will bring your own interpreter. Call 781.477.3882 to request an interpreter. For patients who speak English but may not be able to easily communicate their medical histories, it is advisable that a family member or friend familiar with your medical history accompanies you to the testing.
  • You may experience slight discomfort during the procedure but should be able to resume your normal activities.

FOLLOW UP:

Your doctor will receive a report within 4-5 days after testing and will contact you with the results


Electronystagmogram or ENG Test

ENG is a test designed to give your physician information about the source of your dizziness / unsteadiness. The test takes approximately 2.5 hours. The ENG consists of a series of tasks that stimulate the inner ear and the eyes. You will have electrodes taped near your eyes for the purpose of recording your eye movements. The tasks include watching a moving light, assuming different head positions and caloric stimulation of your ears. The latter portion of the test involves the introduction of warm and cool air into both ear canals.

Preparation for the ENG Test

Typical length of test: 2 – 2.5 hours

  • Come to the test wearing flat or low-heeled shoes.
  • Bring your glasses or contact lenses.
  • Please wash your face thoroughly and remove all makeup before the test.
  • Please abstain from caffeine (coffee, cola, tea etc.) for one day prior to testing.
  • Eat something light prior to testing. Although many people experience some sense of motion sickness, it does not last long. There are no needles or pain associated with ENG.
  • Discontinue nonessential medicines 72 hours before testing, including tranquilizers, sleeping pills, decongestants, antihistamines, muscle relaxants, diet pills, pain and vertigo meds.
  • Continue medications for heart, blood pressure, diabetes, epilepsy, asthma or blood!
  • Arrange to have someone drive you home after the test in the event that you are still slightly dizzy.
  • NSMC provides interpreters for non-English speaking patients; please inform the EMG lab whether you will need the interpreter service or if you will bring your own interpreter. Call 781.477.3882 to request an interpreter.
  • For patients who speak English but may not be able to easily communicate their medical histories, it is advisable that a family member or friend familiar with your medical history accompanies you to the testing.

FOLLOW UP:

Your doctor will receive a report within 4-5 days after testing and will contact you with the results.