Electromyography (ENMG)

What is ENMG?

EMG (Electromyography) is a method of investigation in which the electrical features of muscles, nerves and nerve roots are analysed and their health status is examined.

How is ENMG conducted?

EMG investigation consists of two parts: 1) Measurement of the conduction of nerves, 2) Examination of muscles. One or both of these methods might be applied based on the projected diagnosis. The measurement of nerve conductions is carried out by the doctor or a technician assigned by the doctor, whereas the muscles are only analysed by the doctor. The duration of the investigation ranges between 15 minutes and 1,5 hours based on the planned transaction.

Measurement of nerve conduction: Some nerves in the arm, thigh or other part of the body selected by the doctor are stimulated by means of an electrode placed on the skin. Though the applied electric flow is high-voltage (around 100 watt), it is applied for less than one thousandth of a second and causes no harm. It creates an uncomfortable feeling at the point where it is applied, but this is generally not felt as a pain. The electrical activity generated on the nerve through this stimulator radiates throughout the nerve.The activity on the nerve is recorded by means of a separate electrode. With the help of this recording, the pace of conduction of the nerve and the duration of the reaction created by the stimulator are measured. In one ENMG investigation, around 5-10 nerves are measured in this way.

Examination of the muscles: An electrode with the shape of a needle is placed on a muscle on the arm, thigh or another part of the body and then the electrical activity in the muscle is examined. The electrode usedlooks like injection needles in terms of its size and look. These electrodes are for single use and a new needle is used for each patient, the needle is then discharged (In some single fiber ENMGs, electrodes are not for single use and might be re-used after sterilization). The pain felt during the placement of electrode needle onto the muscle is similar to the pain felt during the injection of medicine into the muscle; however, since no medicine injection is carried out during ENMG, the pain is much weaker. The examination of each single muscle takes about a few minutes. During this time, the needle is kept within the muscle. The direction and position of the needle might be changed a few times in order to obtain records from different parts of the muscle. These transaction generally cause no pain or creates a reasonable pain at an endurable level. The number of muscles to be analysed during an ENMG differs in accordance with the projected diagnosis; 1-10 muscles are analysed generally.

Evoked Potentials: These are the methods developed to analyse the motor and sensual conduction lines in the central neural system. Visual Evoked Potentials (VEP) is used for the analysis of visual line; Somatosensory Evoked Potentials (SEP) is used for the analysis of sensual lines in the spinal cord and the brain; Brainstem Auditory Evoked Potentials (BAEP) is used for the analysis of auditory lines in the brainstem.
Motor evoked potentials is a method used to analyse the motor lines beginning from the brain and reaching to the muscles. It is carried out by means of transcordial magnetic stimulation, which is painless and harmless. In addition to this, by means of this method, a lot of research and examination might be carried out on the working physiology of brain cortex.

Intraoperative neuromonitoring: These are the electrophysiological transactions carried out during the operations about the neural system by using the appropriate and necessary techniques out of all the techniques used at ENMG unit in order to minimize or prevent any damage to the neural system.

What kind of preparation is needed before the ENMG investigation?

You don't need to be hungry before the investigation. The arms must be opened up to the elbow and the legs must be opened up to the knee during the investigation. Sometimes, you may be requested to take off all of your clothes except for your underwear. Therefore, it is advised that you come to the investigation with loose clothes which are easy to take off. You shouldn't put on any cream on your skin since the ekectrical conductivity of your skin is important. Also, your skin must be free of dust, oil and dirt. For similar reasons, you will be required to remove any dressing or bondage on the relevant parts of your body during the investigation. In some cases, the transactions of the patient before you may last longer than expected, then you may have to wait for about half an hour longer than your appointment time. Since the investigation also lasts for about an hour, you are advised to plan to spend about 1,5 hour at the ENMG laboratory.