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EP Testing: A Patient's Guide

Department of Neurology
Hospital for Special Surgery

  1. What is an EP Test?
  2. What are the different types of EPs?
  3. How long do the 2 SSEPs take?
  4. How long do all 4 EP tests take?
  5. What are the preparations for the EP test?

What is an EP Test?

EP, or Evoked potential, is a test that is used to measure the electrical activity in certain areas of the brain and spinal cord. Electrical activity is produced by stimulation of specific sensory nerve pathways. The Evoked potentials measure how quickly and completely the nerve signals reach the brain. less

What are the different types of EPs?

There are 4 types of EP tests:

  • Median nerve somatosensory EPs: They are also called as upper limb SSEPs or MSEP. This test involves application of electrodes on the scalp, neck, above the collar bone, and the wrists. The Median nerve is stimulated at the wrist with very mild electric current. The electric current feels like mild shocks. The shocks are usually painless and well tolerated by most people but may cause some discomfort for some patients. This test may take 30-60 minutes to complete.
  • Tibial nerve somatosensory EPs: They are also called as Lower limb SSEPs or TSEP. This test involves application of electrodes on the scalp, back, knee, and the ankles. The Tibial nerve is stimulated at the ankle with very mild electric current. The electric current feels like mild shocks. The shocks are usually painless and well tolerated by most people but may cause some discomfort for some patients. This test may take 30-60 minutes to complete.
  • Visual Evoked Potentials or VEP: This test involves application of electrodes on the scalp. The visual pathway are stimulated by looking at a changing checkerboard pattern on a video monitor. This test may take 30-60 minutes to complete.
  • Auditory Evoked Potential or BAER or AEP: This test involves application of electrodes on the scalp. The hearing sensory pathways are stimulated by clicking noises generated in a set of headphones. This test may take 30-60 minutes to complete.

How long do the 2 SSEPs take?

60-90 minutes.

How long do all 4 EP tests take?

2 -2 1/2 hours.

What are the preparations for the EP test?

  • Try to avoid applying any lotion or creams because that can cause some difficulties during the testing of SSEPs. Also, avoid using hair gel, because it interferes with scalp electrodes.
  • Patients on medication should take their usual medication on the day of the test unless otherwise advised by their physician.
  • Please bring eyeglasses, if you use them, for the Visual EP.
 

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