For the purpose of diagnosing carpal tunnel syndrome (CTS) there are two types of electrodiagnostic nerve tests generally used... BUT FIRST electrodiagnostic is pronounced Elect-trow-DIE-ag-noss-tick.
This article will talk about the electromyogram (Elect-trow-MY-O-gram) OR EMG for short!
To learn about the second type of test or study
See Nerve Conduction Study (NCS)
An EMG is a test that is used to record the electrical activity of muscles. As you may or may not know, when muscles are used they produce an electrical current of sorts.
Although an EMG test may be used to diagnose CTS, it also can help detect any abnormal muscle electrical activity that can occur in many diseases and conditions such as muscular dystrophy, pinched nerves, ALS (i.e. Lou Gehrigs disease) disc herniation, diabetic neuropathy and others.
EMG's are often ordered in patients who have unexplained muscle weakness. The EMG can help determine between muscle conditions in which the problem started in the muscle ITSELF and muscle weakness due to NERVE DISORDERS.
Patients often ask me....will this test hurt? and the answer is.....Yes, it will hurt some...it will sting, like getting a tiny shot with each needle used.
NEEDLES you say!!... hold on, these aren't your normal shot needles...they are much smaller in diameter.
A small fine needle is inserted through the skin into the muscle. The electrical activity is detected by this needle (which acts like an electrode). The electrical activity is viewed on a screen and then recorded and printed out on a report. Usually several electrode needles will need to be used since muscles are often fairly large. Sometimes the patient may be asked to flex or contract the muscle so a reading during muscle activity can be obtained.
An EMG test should be obtained along with a NCS. The actual test usually takes around 30 minutes. Your doctor should generally test both arms/hands especially if you are having symptoms in both upper extremities or you have an underlying medical condition.
See CARPAL TUNNEL SYNDROME CAUSES. You really shouldn't have an EMG study until you have had symptoms for at least 3 weeks and preferably 6 weeks, unless the injury is from an acute trauma (i.e. laceration, car wreck etc..). If you test too early, the study may be normal since it takes at least a couple of weeks for nerve damage to show up.
EMG's are Falsely Negative in about 5-8% of CTS cases. In other words the test is showing Falsely that you DON'T have CTS when in fact you do....BUT the good news is it's Accurate over 90-95% of the time!
I will list some variables that can effect the outcome of an EMG test:
1) Training- What kind of training does the specialist doing the actual test have?
2) Experience- How long has he/she been doing EMG testing?
3) Use of a technician- Is the specialist doing the actual test ( i.e. insertion of electrode needles)
4) Skin temperature- Cold weather can make the skin colder than normal, make sure your skin temp. is checked before testing is done. If not the test may be inaccurate...and it may have to be repeated.
The specialist is usually a neurologist or physiatrist (Fizz-zy-uh-trist). They should be board-certified in their field of medicine...(example: In neurology - A board certified neurologist). But, they should also be board certified in Electrodiagnostic Medicine.
One report says that only 35% are board certified in electrodiagnostic medicine. Another report showed that 40% of physicians currently doing EMG's are performing studies below the acceptable level!
As far as cost, that can vary by area. In my area a NCS/EMG for upper extremities cost around $450.00. Remember, that an
EMG test for carpal tunnel syndrome is a valuable test in diagnosing CTS...especially when done in conjunction with a nerve conduction study.
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