Hello I'm Bob Whitten, a physiatrist at Mayfield Brain and Spine.
My area of speciality is electro-diagnostic medicine more commonly known as electromyography
or EMG and nerve conduction studies.
These are tests that measure the electrical activity of the muscles
and nerves in the body.
These tests can tell how well information is transferred from the brain,
down to the nerves in the arms and feet,
or, from the nerves of the hands and feet back up to the brain.
They can help identify different types of disease or injury to the nerves,
it can also be helpful to your physician in determining what further treatment might be needed.
I have been diagnosing and treating patients for several decades, and I know that many
of you are in pain, so I'll try to minimize the discomfort of the test.
I'll try to work efficiently to get the test done as quickly as we can, but we want to
make sure that we get the information your physician needs
to make the determinations for your treatment.
First, I'd like to show you how nerve conduction studies are performed,
and then I'll demonstrate an EMG.
Generally speaking, the nerves of the body are broken into two major groups.
SENSORY NERVES are nerves that transmit things like hot, cold, sharp, dull; transmitting information from
the tips of your fingers or toes up into your spinal cord and ultimately to the brain.
In the opposite direction, you have nerves that transmit from the brain and spinal cord,
down to the muscles of the hands or feet.
These are the MOTOR NERVES.
This machine has the ability to separate the difference between motor and sensory nerves,
and this is important because different diseases or disease processes, can affect different
parts of the nerve.
So what I've done here, is set up a study for the radial sensory nerve.
Remember, the sensory nerves are the nerves transmitting from the tip of the finger back
up to the brain, and what you can see here, is there are three electrodes.
We have the ground electrode, and the two active electrodes, these are around the finger
that the radial nerve goes to.
We're going to be stimulating ten centimeters back from this, and we're going to see if
we can elicit an electrical response.
The way we do that is, there is a small stimulator. The current flow we use is quite low.
It does not do any harm, but it is what I'd usually describe as unpleasant.
The first few shocks are relatively mild and may not even be felt, but then we have to
increase it until the nerve tells us when to stop.
I'll show you what I mean. We'll put pressure here, okay, Jeremy, you may feel a small shock,
the first shock will come now and again now.
And again now and again now and you may notice there's a little bump right here that's actually
your radial nerve talking back to us, its size shape and speed
tell us how healthy that nerve is.
I'm a going to go one more shock, a little stronger. And you notice, it didn't get much bigger.
Now we're going to check and see how big that shock is.
So the shape size and speed of that bump, give us clues about a nerve cell body,
that's actually located about a half an inch off your spinal cord,
up around where your ear joins your head.
I had a patient one time look at me and say, "Wait a minute doc you shocked me on my wrist,
you measured on my thumb.
How can you be checking in nerve in my neck?"
And that's a good question.
It helps to understand, that in one manner, our nerves are set up like the electrical
circuits running from the fuse box in our house.
All of the electrical power comes into the circuit box, and goes through the breakers,
before traveling to all of the circuits in our house.
Suppose you know that circuit breaker number four, goes to the upstairs bathroom light
the hallway and first bedroom.
You come home and someone says, "the lights in those areas are out and one of the fuses have blown",
you would know to go down to the circuit box and flip the number four breaker.
In a similar manner, all of the nerves to our arms or legs, extending out to our hands
or feet, must originate in, or near, our spinal cord.
And, in the majority of patients, follow a set pattern
to the different parts of the limbs.
In the same manner, all the circuits down here in your thumb had to originate up near
that fuse box in your neck, and the nerve cell body that creates that,
is about a half-inch off the spinal cord.
What we're going to do now is the peroneal motor nerve on the left leg.
I've set up reference electrodes; the green, the red reference, and the active electrode.
I'm going to stimulate the peroneal nerve.
The way we'll do that, is in the front of the ankle.
Jeremy, you're going to feel a small shock.
Now.
It's going to get stronger.
Now.
Your foot may move.
A bit stronger still.
And we get a little bit of a bump on the screen.
We're going to go stronger, still. The bump got a little larger.
and your foot moved more, so we're going to stimulate one more time.
One more time, and that time it didn't get any larger.
That tells us that that we have a maximal response.
We're now going to check the same nerve, in a second place.
This time, up around your knee.
You're going to feel one strong shock.
Once. More, muscles will move. Now.
Very good, and we see the same response from the ankle.
Now move to the right, and we're going to measure the distance between those two shocks.
By measuring the distance between the two shocks, we can actually calculate how fast
the nerve transmits from your knee down into your ankle.
Let me put that in.
And again that's just one more thing we can do to see how healthy the peroneal motor nerve is.
So after we complete the nerve conduction studies, that's the good news; there's some bad news.
We have to do the EMG.
That involves the use of a small pin.
I have patients ask me, "Doc, why do we have to do the pin exam?"
And I think that's a great question.
We do the pin exam to listen to the muscles talk.
I'm going to make a bet here.
I'm going to bet that you've heard a muscle talk before and didn't realize it.
If you've ever gone to the hospital and visited someone in the intensive care, or in the critical
care unit, you remember that they had leads on their chest.
And if you could see the monitor over the bed you knew, that every time their heart beat,
you'd see that spike in a wave on the screen.
You knew that that spike in the wave, somehow is being made by their heart when it beats.
What does that tell you?
Well, that tells you that the heart, which is a muscle, when it contracts to pump the blood,
generates an electrical signal, that if you can capture and analyze, can tell you something.
The doctor or nurse could look at that monitor, or say, a series of traces, like an EKG, and
they could tell if the heart had been damaged.
They could also tell if there was any damage to the nerves of the heart, and what they
really mean.
So what is true for the heart and EKG, is actually true for any muscle in your body
called the EMG, or Electromyogram.
Which is what I'm doing now.
Now we run into a bit of a problem, if you think about it, you have a small muscle in
your forearm, that wiggles, just the tip of your finger.
But he's surrounded by much bigger muscles, that move your wrist and hand.
How do we listen to just that little muscle talk?
Well, we have to take the antenna, and put it in the muscle,
and that's what the pin is.
We don't inject anything, there's no biopsy.
The purpose of the pin is to pick up the electrical signals from the smaller muscles.
So what we have here is a set up for an EMG
for one of the forearm muscles of the right arm.
You'll see again, we have a ground electrode, and a reference electrode, but in this case,
the active pickup is the tip of the pin.
This pin is a disposable pin.
It has not been used on anyone else and we'll discard it after we do the test on Jeremy.
The pin is actually quite small and teflon coated, so that glides into the skin easily
and into the muscle. And what it will do
is actually pick up the electrical activity the muscle creates when it contracts.
Jeremy, you'll feel a small bit of pressure and a pin stick right, now.
Now, what you'll hear is like a 'chik-chik-chik' sound.
And that is actually the muscle talking back to us.
And that sound right there.
It was actually Jeremy, activating one of the muscles.
So, let it rest.
We're going to hear a chik-chik-chik sound.
And, if you look on the screen you can actually see those little 'chik-chik-chiks' being formed
on the screen.
That's one way of listening to the muscle at rest.
But now we're going to get Jeremy's brain involved.
We're going to actually have them activate and see how the muscle activates motor units.
Jeremy, I want you to very gently bend your wrist back, just hold it right there.
Good job.
And you can hear already, it gets noisier.
And if you look at the screen, you can see several spikes.
And if you look down here, you can see again, a nice pattern.
We're gonna have you bend it back more, and more, and more.
Hold it there, good and strong.
Don't let me push it down.
And it gets quite noisy... and relax it, all the way down.
Now, if you look, you can see where it went from noisy, to very noisy.
Actually whiting out the screen, and then as he relaxed, all the motor units faded away
and now we just have baseline activity.
So the way we analyze the muscle with the pin exam, is how big, how fast, how often,
and how crowded are the motor units.
And the two screens, that one at the top giving us a bigger view of individual motor units,
and the lower screen that looks at the crowding, give us those clues.
For more information about EMG's or conditions that affect the spine.
Please check our website at MayfieldClinic.com.