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How is an EMG performed?
In a typical study, the patient is laying down, usually on the back. Different circumstances may warrant other positions, and I do try to be adaptable. In each session, several muscles are tested. Nerve injury will create specific patterns of muscle abnormalities, and by testing several muscles, we are able to tell where the site of injury is. EMG is only useful for testing injury to motor nerves, or nerves that go to muscles. It tells us nothing of sensory function. Therefore, if the injury has been only to the sensory portion of the nerve, the test will not be helpful. Also, if one thinks of a nerve as a wire with a conductor and an insulator, damage may occur to the wire, the insulator, or both. It is typically thought that more severe injuries include damage to the conductor, and these are less able to heal. EMG will only show an abnormality if there is damage to the conductor. Therefore, the EMG can give information about severity of injury as well as prognosis for recovery.
In a typical study, 4 - 8 muscles are tested, and each muscle takes 5 - 10 seconds to test. While the pain of the test is minimized by using a fine gauge needle, it still is a needle, and there is some amount of pain involved. Generally, smaller muscles are more painful and larger muscles less so. The muscle tested may be sore for several hours after, but it is unusual for the soreness to last more than 24 hours.
How is a Nerve Conduction Test Performed?
A Nerve conduction test is performed in a medical office with an EMG/NCS machine. Nerves conduct just like an electrical wire, so the test is performed in a manner similar to that an electrician would use when testing a wire. A probe is placed over a nerve, and an electrical impulse is delivered in gradually increasing intensity until the desired response is obtained on the computer screen. The maximal stimulation is enough to make the muscle jump. While many patients find it "neat" to watch their muscle jump involuntarily, most consider it a "strange" feeling. Only occasionally do patients consider it painful. The probe leaves no permanent marks, and does not cause any bleeding. Sometimes the stimulation will cause tingling that will last for more than a few minutes. Rarely does it last longer than that.
Most nerves are tested in several places, and several characteristics of the nerve are measured and recorded. In a typical study, several nerves are tested, and several aspects of each nerve are tested. For example, we typically test the motor, sensory, and late wave characteristics of the nerve we are worried about, as well as a control nerve we are not worried about for comparison. Sometimes, we will test the same nerve on the opposite side, also for comparison.
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Preparing for your EMG/NCS...
Do...
- Plan on being at the office for 45 - 60 minutes. The length of time a study takes varies depending on the condition. Most studies require a half hour or less. More involved studies, such as conditions affecting more than one extremity may take more than an hour.
- Take all of your medications as you normally would.
- Arrive 15 minutes early.
- Bring or wear loose fitting clothing. For neck and arm studies, it is helpful to wear a sleeveless shirt. For back or leg problems, bring shorts.
- Inform Dr. Nagel if you take anti-coagulants such as Plavix or Coumadin. You do not need to stop them, but it is important for him to know you are taking them.
- Inform Dr. Nagel if you have a tendency to pass out with needling. He doesn't like surprises!
- Inform your primary care physician in advance if you have a condition for which you would normally take antibiotics for dental work, such as a heart murmur, an artificial heart valve, an artificial joint, etc. In general, for EMG/NCS, prophylactic antibiotics are not required, but that decision should be made by your regular doctor.
- Inform Dr. Nagel if you have a pacemaker or other electrical device (spinal cord stimulator, etc.), although these devices are not a contraindication to the test.
- If you feel you may need pain medication after the procedure, please contact the doctor who regularly prescribes your medication. It is not advisable to get pain medication from multiple doctors. In certain circumstances, doing so can be considered illegal.
- If you feel you need sedation, please contact your regular or referring doctor for a prescription. It is rare patients need sedation. If you do feel you need something, Valium or one of its relatives is usually used (Xanax, Ativan). You need to be awake for the procedure, so whatever you take should allow you to be relaxed, not drooling!
- Plan on working that day after the procedure. It is rare that post-procedural pain is sufficient to warrant time off from work.
- Let Dr. Nagel know who your primary care doctor is so he can forward a copy of the results to him or her. Also, let him know any other doctors who should receive copies of the results.
- Call your primary care physician if post-procedural discomfort lasts more than 24 hours.
- Come prepared with a joke or story to share. It makes the time more enjoyable!
Don't...
- Prepare for a ride. It is rare for a patient not to be able to drive after the test.
- Bring insurance forms to be completed. All insurance forms must be completed by your referring or primary care physician.
- Wear lotion on the extremity to be tested.
- Ask Dr. Nagel for notes or opinions on work capacity. All such opinions need to be made by your primary care or referring physician.
Risks...
- Exacerbation of underlying pain problem. This usually lasts less than 24 hours, but may last for several days. If this pain lasts more than a few days, contact your referring MD.
- Soreness at stimulation or needling sites. This usually only lasts a few hours. If this lasts more than 24 hours, contact Dr. Nagel.
- Bleeding/bruising. This is normal, and can be minimized by icing. Severe bleeding is not known to happen, even in patients taking anti-coagulants.
- Infection. This is rare. If you do have a fever more than 24 hours after the procedure, please call Dr. Nagel and your primary care physician.
- Pneumothorax. This is collapse of lung which can only happen when muscles of the chest region are tested, and is easily avoided by proper technique.
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