The Joy Of Evoked Potentials
Last updated: April 2023
The process of diagnosing someone with Multiple Sclerosis is not easy. There is no one test that guarantees you have MS. Instead, doctors rely on a series of tests and then look at the combined results to help make the diagnosis. In the past, I’ve shared my experience with a few of these tests, namely the MRI and spinal tap. Today, I want to talked about my experience with the other common test used in a Multiple Sclerosis diagnosis, Evoked Potentials.
What are Evoked Potentials tests?
When I was going through the process of getting diagnosed and was told I’d be having some Evoked Potentials done, I had zero idea of what they were talking about. MRI, sure, I knew what that was. Spinal tap, OK, I had a pretty good idea of what that was too, at least in the most general terms. This other test was extremely foreign to me. Was I going into another dark tube? Or getting some fluid extracted from some other part of my body? How painful and scary was this going to be?
Turns out, not really as tough for me as the other exams. Evoked potentials are a series of tests that help measure and record the electrical activity of the brain in response to stimulation. Essentially, they help identify the delay of signals from the brain to other parts of the body. In MS, the signals our brain is sending throughout the body often don’t make it to their destination as fast as they should or at all. That’s because the myelin layer around the nerves (where these signals travel) is damaged or eaten away by our own immune system. So measuring the speed that it takes for signals to travel can be a way to identify this type of myelin damage.1-3
Wait, are they going to electrocute me?
While it may sound a little scary and painful, it really isn’t. You get a number of electrodes attached to various parts of your body, with a conductive gel, you are then subjected to different types of stimuli. Some examples: Looking at a screen with an alternating checkerboard pattern, just sitting there and looking at it, no big deal (this is a Visual Evoked Potential test). Putting on some headphones that play a series of clicking noises, again, nothing too strange about that (this is a Brainstem Auditory Evoked Potential test). Then the interesting one, where short electrical pulses were sent through my arms and legs (the Sensory Evoked Potential test). It was maybe a little startling but not at all painful to me.3
How’d it go?
These tests were most definitely the easiest of the big three MS exams to me. It may feel a little weird to have a bunch of electrodes attached to you, but for someone with a touch of claustrophobia, I’ll take that over an MRI any day! While the doctors were already pretty sure I had MS by the time I took these, the Sensory Evoked Potential really confirmed it. The signals in my right arm and leg were not traveling at the speed they should have been. Even though I had only been having problems with my legs at the time, this showed that there was damage in areas that I couldn’t notice.
To me, my right arm seemed to be working with no issue, but through Evoked Potentials, they were able to identify another demyelinated area. Sure enough, over time, visibly noticeable issues developed with my right arm. The early damage picked up in the Evoked Potential worsened over time as the myelin was slowly damaged. Being able to identify an area that seemingly has no symptoms is one of the main benefits of these types of exams (a great reminder that just because someone may seem symptom-free, doesn’t mean that damage isn’t still happening).
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