5/14

I have my EEG appointment tomorrow at 9 a.m. These tests total approximatly 2 hours in length.

An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain by using sensors attached to your head and connected by wires to a computer. The computer records your brain's electrical activity on the screen or on paper as wavy lines. Certain conditions can be detected by observing changes in the normal pattern of the brain's electrical activity.

Evoked Potential (EP) tests
Evoked Potential tests are procedures for measuring the speed of impulses along neurons. These tests help point our lesions that are not causing symptoms by providing evidence of slowed nerve impulses.

Responses can be measured using EEG readings from electrodes attached to the scalp and occasionally other areas of the skin. They are in fact completely painless and entirely harmless. Based on input signals to the particular sense being measured, the time taken for that response to register can be accurately measured and compared to normal readings. The results are then analyzed on a computer and average speeds recorded.

Demyelinated neurons transmit nerve signals slower than non-demyelinated ones and this can be detected with EP tests. Although they may appear to function perfectly, even remyelinated neurons are slower than normal nerves and so historical lesions can be detected in this way.

There are three main types of evoked potential test: (and I believe will all be performed tomorrow)

Brain-stem Auditory Evoked Response (BAER)
The BAER test measures the speed of impulses along the auditory portion of Cranial Nerve VIII. This nerve arises in the Pons area of the brain-stem and therefore this test may be indicative of lesions in that area. The patient lies down in a darkened room to prevent visual signals from interfering with measurements. A series of clicks and beeps are played back to the patient. 67% of people with definite MS and 41% of people with probable MS will have abnormal BAER test results.

Somatosensory Evoked Potential (SSEP)
The SSEP test pertain to sensations in skin and deep tissue. These measure the conscution of impulses by applying electrical stimulus to the arms or legs. The current is switched on for 5 seconds and electrodes on the back and skull measure the response at particular junctions. The current is very low indeed and completely painless. The electrodes record neural signals when they reach the scalp. The speed of various nerves can be measured in this way and the points of slow-down (i.e. demyelinated lesions) approximated to because of the sampling at several places. 77% of people with definite MS and 67% of people with probable MS will have abnormal SSEP test results.

Visually Evoked Potential (VEP)
This noninvasive test measures the speed and amplitude of the of the optic nerve impulses. The patient has to focus on the center of a "TV" screen on which there is a reversing black and white checkerboard pattern shown at measured intervals. The patient wears a patch on one eye for a while and then on the other, so that the speed of both optic nerves can be measured. The electrodes placed on the back of the head to record cortical (outer layer) signals record when the nerve impulse is received. 85-90% of people with definite MS and 58% of people with probable MS will have abnormal VEP test results.

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5/23: I have an appointment at 9 a.m. for 3 MRI's (brain, c-spine and thoracic), but these will be MRI's with contrast. To gain better contrasts in the images, contrast agents such as Gadolinium are often injected intravenously (FYI: Gadolinium is a non toxic substance which does not contain iodine and has practically no side effects.) The gadolinium works by altering the local magnetic field in MS lesions and thus enhancing the MRI image. This helps to differentiate between new/active and dormant lesions. So, this would then illustrate whether this is my first attack or not.