BandersnatchF
Well-known member
A single poke can test multiple nerve fibers if the probe is moved around a small amount. Each small movement (in or out, left or right, etc.) tests a different nerve fiber from the same root. Suppose that just 20% of the nerve fibers are affected. Testing 7 sites (which can be done by doing the center and a small move in each of the six directions) means that the chance you'll find at least a single affected fiber is 1-(0.8^7) = 80%. Also, there are other signs they're going to look for, like reduced recruitment and irritability on insertion. If they find those, they're going to check more carefully for other stuff.
If damage to a nerve root is even suspected (I had a single complex repetitive discharge, which is a sign of chronic nerve injury), the EMG tech will check other muscles / fibers on that nerve root. I had an extra set of pokes on a muscle higher up on the same root as my tibialis anterior. No abnormal signals other than the single CRD. My neuro (who did the EMG test) concluded that the CRD fell into the same category as the fascics that showed up in four muscles—very likely benign, with any damage due to nothing more serious than a slightly pinched nerve (this is very common).
Bottom line: an EMG will catch some signs that there's a problem if there is one. It may not be definitive (ask CosmicVisitor about that) and it often isn't due to A/L/S (there are a lot of things that can cause unusual EMG signals, including "nothing in particular"), but something will show up. Keep in mind, too, that twitching in A/L/S is a sign of nerve damage that an EMG will pick up. Fasciculations on an EMG are of no consequence unless they're accompanied by other abnormalities, according to a long-term study of medical personnel with benign fasciculations.
If damage to a nerve root is even suspected (I had a single complex repetitive discharge, which is a sign of chronic nerve injury), the EMG tech will check other muscles / fibers on that nerve root. I had an extra set of pokes on a muscle higher up on the same root as my tibialis anterior. No abnormal signals other than the single CRD. My neuro (who did the EMG test) concluded that the CRD fell into the same category as the fascics that showed up in four muscles—very likely benign, with any damage due to nothing more serious than a slightly pinched nerve (this is very common).
Bottom line: an EMG will catch some signs that there's a problem if there is one. It may not be definitive (ask CosmicVisitor about that) and it often isn't due to A/L/S (there are a lot of things that can cause unusual EMG signals, including "nothing in particular"), but something will show up. Keep in mind, too, that twitching in A/L/S is a sign of nerve damage that an EMG will pick up. Fasciculations on an EMG are of no consequence unless they're accompanied by other abnormalities, according to a long-term study of medical personnel with benign fasciculations.