What to expect from your nerve conduction and electromyography tests
You can’t treat it if you don’t know the cause.
Nerve conduction and electromyography are two really powerful diagnostic tests I use in the first pillar of my unique Five-Pillar system – Identify.
It’s only natural to feel a little nervous about these tests. Who wants to submit to an electrical shock or a needle stuck into a muscle? Well, I’m here to ease your anxieties, break down the two examinations, and answer your questions.
Before we get into how these tests work, let’s talk about nerves.
Imagine a wire, any old wire. If you were to take a pair of wire cutters and chop that wire in half, what would you see inside?
At the center, you’d see the metal – that’s the wire itself. Maybe there are multiple wires. Around the wire, you’d see rubber or plastic – that’s the insulator.
Nerves are structured much the same as any regular household wire. In the center, you have the nerve itself, which is called an axon.
The axon is wrapped in a fatty material called myelin. In the peripheral nervous system, –myelin is produced by the Schwann cell.
Nerves that are heavily wrapped in myelin – which kind of look like the Michelin Man with all of his ripples – conduct their electrical signal faster. Fast-conducting nerves are usually motor nerves and specialized sensory nerves, which help us human beings do essential and, quite frankly, incredible things like stand on our two feet and not fall over.
These large-diameter nerves allow the brain and spinal cord to constantly detect where our bodies are in space. And these are the nerves we evaluate with nerve conduction testing.
In many cases, small fiber nerves are damaged before the large fiber nerves. Small fibers are so tiny that nerve conduction testing can’t detect abnormalities in them. If nerve conduction testing is a magnifying glass, then we need a microscope to examine small-diameter nerve fibers.
If together we suspect you have small fiber neuropathy – which usually feels like a burning or tingling sensation, first I’ll use a nerve conduction test to exclude large fiber neuropathy. When that’s done, I’ll do a near-painless procedure called a skin punch biopsy, which, you guessed it, is scrutinized under a microscope, and confirms the diagnosis of small fiber neuropathy.
First up, nerve conduction testing
If I am evaluating weakness thought be due to a peripheral nervous system disorder, I’m going to start with a nerve conduction test. If I am really 100 percent sure that the problem is specifically in the muscle, I’ll skip ahead to the EMG or what I call the needle portion of the exam.
So, what happens? Well, nerve conduction testing uses electricity. Your nerves don’t just look like electrical wires; they behave like them, too. So, we use a nerve conduction testing machine and two devices called a stimulating electrode and receiving electrode to apply an electrical signal to the nerve.
These electrodes are applied to different parts of the body – that might be your hand, foot, leg, and so on. If I’m testing for carpal tunnel syndrome, for example, the receiving electrode will sit around the hand, just above the wrist, and around the elbow.
The stimulating electrode is also applied to a specific area of the body, depending on the nerve being tested. I use a tape measure to measure along the arm or leg or wherever we’re going to be testing to ensure it’s perfectly positioned.
Then, I press a button that sends the electrical pulse between the stimulating electrode, along the nerve, to the receiving or recording electrode.
Now, a lot of people are afraid of nerve conduction testing. No one likes to get a shock, but is it actually painful? I’ll be honest – it is a little uncomfortable. At first, it’s so mild it feels like a slight tickle. As the test progresses, it can get a bit more intense, but I promise it’s really not too bad.
I have tested people of all ages and all genders, and it’s very uncommon for someone to tap out. The shocks are so brief – really a fraction of a second – that by the time you register the discomfort, it’s all over. No one needs sedation, and we don’t use numbing medicine.
Now, remember myelin surrounding the nerve? If the conduction is slow, the myelin is affected. (Recall that under normal conditions myelin enhances the speed of electrical conduction along the nerve axon.) Before we go any further, I have to introduce you to the most important measure of the nerve conduction test which is called an action potential.
Here’s a good way to think of action potential. Imagine two people holding a rope. The rope isn’t tight; there’s a little slack to it. Now let’s say one person flicks their wrist. They’ll see waves travel along the rope toward the other person. That’s action potential.
When I stimulate a nerve, it sends an electrical signal just like that wave traveling along the rope. The height of the wave reflects the health of the axons. The more axons you have, the taller the action potential. The fewer axons you have, the smaller the action potential. There is a range of normal. But when axons are damaged by disease the action potential is smaller than expected. This is called axonal neuropathy.
Furthermore, the more slowly the action potential travels along the nerve from the stimulating electrode to the recording electrode the more severely the myelin is affected. Again, there is a range of normal. But when the conduction speed (or velocity) is too slow we have a demyelinating neuropathy.
I’m also looking at the action potential – the more the axons can pick up electrical stimulation from the nerve conduction test, the larger the action potential.
Depending on the neuropathy a person has, I can determine if that neuropathy primarily affects the axon or myelin. The height of the action potential relates to the axon. The speed of the action potential relates to the myelin. Simple as that.
Many auto-immune neuropathies tend to be more demyelinating, which shows changes in conduction velocity.
Entrapment neuropathies like carpal tunnel syndrome will primarily, or at least initially, present with slowing. Think of a highway that goes from four lanes to one lane and back to four lanes. Everything gets backed up and traffic slows down. But, if left untreated, the axon becomes damaged, and muscle loss occurs. In the case of median neuropathy at the wrist (carpal tunnel syndrome), a person ends up with atrophy of muscle in their hand. That’s very serious. That’s what I call the do-not-pass-go, do-not-collect-$200. In other words, go straight to the surgeon and get the problem fixed.
Let’s talk electromyography (EMG) testing
Next up, let’s look at the electromyography component.
For this test, we use a sterile, single-use needle, which is actually an electrode that measures the electrical signal in the muscle. So, I’m not injecting anything.
Again, patients are naturally worried about the pain. Many times, however, because the needle is so thin, my patients do not feel it at all.
Electromyography is used to detect changes in the muscle motor unit which consists of the muscle fiber, the neuromuscular junction, and the nerve ending that secretes its chemical signal, called acetylcholine, into the neuromuscular junction where it is picked up by specialized protein receptors. When nerve axons are affected by disease or trauma it produces changes in the muscle motor unit that can be detected during the EMG. These changes include spontaneous electrical discharges of the muscle that occur without muscle contraction (when the muscle should be at rest). These changes are called fibrillation potentials, positive sharp waves, and fasciculations. While the first two are only detectable by the EMG machine, fasciculations can be visible to the naked eye. Sometimes, fasciculations are described as having the appearance of “worms below the skin.” Fasciculations are a classic finding in Amyotrophic Lateral Sclerosis (ALS) or Lou Gehrig’s disease. However, fasciculations can be seen anytime the motor nerve axon has been damaged. It is very important to keep in mind that if you have fasciculations it does not automatically mean you have ALS, but you should definitely get checked by a qualified neurologist.
When nerve disease or damage has been present for a long time, because the motor unit attempts to repair itself, contraction of the muscle during EMG testing produces what are called, “large amplitude, polyphasic motor unit potentials.” We call this chronic denervation.
EMG is also used to detect muscle disease. In severe inflammatory muscle disease, it is also possible to see fasciculations and positive sharp waves. But the main finding in muscle disease on EMG is are called short duration, low amplitude polyphasic motor unit potentials with muscle contraction.
Polyphasia means lots of up-and-down squiggles visible on the EMG screen.
In practice, during EMG, I choose the muscles I want to evaluate and insert the needle into the muscle. I listen to the muscle at rest – when you’re not moving. Then, I’ll ask you to activate the muscle. Muscles have fibers, and as you put increasing tension on the muscle, you’re basically bringing into play more and more muscle fibers (or motor units) until you reach a maximal contraction.
Get the answers you deserve
I do nerve conduction tests and EMGs all the time here at Sharlin Health and Neurology. I’ve been in practice for about 30 years, and I like to quote former President George W. Bush when I say, “I’m the doctor who does the kinder, gentler EMG.” Because people come and see me, and they say, “Oh, I had one. It really hurt!” I’m like, “It’s going to be okay. I do the kinder, gentler EMG.”
And they love it.
So, come to me, and rest easy knowing I’m not going to make you terribly uncomfortable. I’m going to chat and get to know you. By the time we’re done with the test, you’ll be completely relaxed, and we’ll have some good information about what’s going on.
Remember, no matter what direction you choose for your neurological care, identifying the problem correctly is the first step. It’s part of my unique Five-Pillar system and a critical even if you are looking for functional medicine approach approach.
Once we’ve clearly identified the problem, we can talk about various solutions, investigate those root causes, and determine how we can utilize my team, and myself, to take that deep dive and give you that personalized action plan that ultimately gets you the results you want.
Sound good? Schedule your initial consultation today.