NCV and EMG explained

[Guest guest]

Jyll,

Here's some info for you below. These tests are used in many

disorders. In CMT the testing results can distinguish between Type 1

and Type 2.

~ Gretchen

http://www.teleemg.com/new/emgfaq.htm

Your doctor has just ordered a test called an EMG. EMG stands for

Electromyogram which loosely translated means electrical testing of

muscles but in fact has come to mean electrical testing of nerves

and muscles. The EMG is performed by a specialist, the

Electromyographer, who is usually a Neurologist or a Physiatrist.

Parts of the test (the nerve conductions) may be performed by a

specially trained technician. It is an in-office procedure and does

not require hospitalization. On average, an EMG takes anywhere

between 30 minutes and 2 hours, depending on how extensive a testing

your doctor orders on you. It can be done at any time during the day

and, with few exceptions, does not require any special preparation.

Sometimes EMGs are thought to be a treatment of some sort, or a type

of acupuncture. This is not true; an EMG is only a test, much like

an EKG or an X-ray are tests and not treatments.

What are some problems for which EMGs are ordered?

EMGs are usually ordered when patients are having problems with

their muscles or nerves. They test the nerves and muscles of the

body's extremities, looking for a problem in either one of these

areas. An EMG may be ordered to see if you have a pinched nerve in

the back or the neck. If you have tingling or numbness in your arms

or legs, an EMG may show if you have a nerve entrapment somewhere or

a nerve injury. Weakness of the muscles or " fatigue " (tiredness) may

be indicative of nerve or muscle disease and require an EMG. There

are many other medical problems that might suggest the need for an

EMG. If you have any doubts as to why you need this test, ask your

doctor.

What happens during an EMG?

During this test, you will be lying on an examination table, next to

an EMG machine (which looks like a desktop or laptop computer). The

test consists of two parts, though at times one may be done without

the other. The first part is called Nerve Conduction Studies. In

this part some brief electrical shocks are delivered to your arm or

leg in an effort to determine how fast or slowly your nerves are

conducting the electrical current and therefore in what state of

health or disease they may be. You see, a nerve works something like

an electrical wire. If you want to see if the wire is functioning

properly, the easiest thing to do is to run electricity through it.

If there are any problems along its length, you will know it by a

failure of the current to go through. To do this, the doctor will

attach small recording electrodes to the surface of one part of your

limb, and will touch your skin at another point with a pair of

electrodes delivering the shock. When this happens, you will feel a

tingling sensation that may or may not be painful. Between the brief

shocks you will not feel pain. As there are several nerves in each

extremity which need to be tested, the procedure is repeated 3 or 4

times or more per extremity studied. The amount of current delivered

is always kept at a safe level. Patients wearing pacemakers or other

electrical devices need not worry since this current will rarely

interfere with such devices. During the nerve conduction study, the

doctor or the technician performing the study will occasionally be

pausing to make calculations and measurements.

The second part of the test is called Needle Examination and as the

name implies, involves some needle sticking. The needles used are

thin, fine and about one and a quarter inches long. This part tests

the muscle to see if there has been any damage to it as a result of

the nerve problem or if the disease involves the muscle itself

rather than the nerve. Usually 5 to 6 muscles are sampled in one

extremity, but occasionally, if you have problems in more than one

area, additional muscles may need to be studied. The needle is

usually inserted in the relaxed muscle and moved inside gently in

order to record the muscle activity. When this is done, you will be

able to hear the sound of the muscle activity amplified by the EMG

machine; it will sound something like radio static. The painful part

of this section is when the needle is first inserted through the

skin since all of the pain receptors are located in this area. Once

inside the muscle, the sensation is usually perceived as discomfort

or pressure rather than pain. During the needle exam, no electrical

shocks are delivered. Also, since the needle probe is used here only

as a recording device, no injections are given through the needle

into the muscle. On the average, a muscle can be sampled in 2 to 5

minutes though this may vary with the type of problem being

investigated.

How long does an EMG take?

The nerve conduction part of the test usually takes longer than the

needle exam because one needs to make calculations and measurements

during it. On average, if one extremity is studied, the nerve

conductions take anywhere between 15 and 30 minutes. The needle exam

for one extremity usually takes 15 to 20 minutes. You can count on

being in the examination room for about one hour if only one

extremity is requested; longer if more extremities need to be

tested.

What kind of preparations are necessary for an EMG?

Few preparations are needed on the day you have an EMG. You do not

need to fast, or eat any particular kinds of food before the test.

You can drive yourself to and from the test, so you do not need to

bring a friend or a relative with you, any more than you would say

if you went to the dentist. You can count on resuming your regular

activity after the test is completed. As for clothing, it is not as

much what you wear as it is what you don't wear. Since in a great

majority of cases the low back and buttocks area may need to be

studied or in cases of neck problems, the back of the neck and

shoulder areas studied, it is best not to wear clothes which will

interfere with access to these areas.

With few exceptions, you may continue taking medication prescribed

by your physician as ordered without this interfering with the EMG.

However, if you are taking a blood thinner, you should notify the

Lab where your EMG is being done, since in that case the needle part

of the test may cause bleeding inside the muscle. Also if you are on

any medication for Myasthenia Gravis such as Mestinon or other, your

medication may interfere with the test, so you should also notify

the Lab. If you have any doubts about other medications you are

taking, it is best to check with the Lab to be on the safe side.

Can I ask for some pain medication?

Different labs have different policies about pain medication. Some

physicians may recommend you take two Aspirins or Tylenols before

the test. Others may mail you a prescription drug to take an hour

before the test. Sometimes you may be given an injection prior to

the test. It is common however, that no sedation is given in any

form since in most instances, patients wish to return to work or

other regular activity after the test is completed. Another reason

for not giving sedation is that you should always have someone

accompany you to drive you home after receiving sedation and this is

not always easy to arrange.

How soon will I find out the results?

Though the physician performing the test has a general idea of what

the findings are during the test, the full results are only arrived

at after more calculations and measurements are performed after the

end of the test. The results are therefore usually not ready until

later that day or even the next in complicated cases. They are

usually not released directly to the patient. Instead they will be

conveyed to the referring physician since he or she has to assess

the results in light of the patient's other findings.

How much will an EMG cost?

As a rule the more areas you need studied, the more the test will

cost. However costs may vary from one physician to another and is

different in different states. It is always best to inquire about

cost with your physician.

Most insurance policies cover EMGs, though frequently the coverage

is not 100% and the primary care or insurance physician will have to

OK it before it can be ordered. It is best to have your doctor's

office find out what kind of coverage you have for an EMG.