Electromyography

Electromyography is abbreviated as EMG. It is a valuable test that can bring a lot of information about the function of nerves, muscles and neuromuscular junctions and helps to diagnose diseases affecting these structures.

 

The movement of our skeletal muscles is controlled by the brain. From there, the neuroelectric signal gets to the spinal cord and from the spinal cord it is guided by peripheral nerves towards the muscle fibers. The connection between a nerve and a muscle is called neuromuscular junction. The junction changes the neuroelectric signal to a chemical instruction that is conducted from the nerve ending to the muscle fiber, causing its contraction.

Principle

The EMG is usually performed by neurologists. They use an electromyograph machine, which is a recording apparatus with electrodes. The device uses stimulating electrodes and a scanning electrode. The stimulating electrode is taped to the skin a the site of the examined nerve. The scanning electrode can be attached to the skin over the examined muscle, but the results are not accurate. Therefore, it is preferred to use a needle electrode, which is pushed directly into the muscle. It hurts a little, but the quality of the examination is significantly improved. After the electrodes have been applied, the patient is asked to perform careful movements with the investigated muscles. The device shows changes of electric potential and it is also possible to simulate a neural signal by an electric stimulus from the stimulation electrode.

Preparation

The examination does not need any special preparation. The patient can eat and drink normally and take any chronic prescribed medications.

Indications

A trained physician can evaluate the conduction of record nerve signals to the muscles and their contractions, which allows diagnosing disorders of the nerves (neuropathies) and muscle disorders (myopathies) and assessing their severity. EMG is used in diagnosis of conditions associated with loss of muscle tissue, polyneuropathies, myasthenia gravis, Duchenne muscular dystrophy, carpal tunnel syndrome, etc.

Disadvantages

The only problem is a mild pain when the needle electrode is inserted into the examined muscle. The are no other important disadvantages. Because the used needles are very thin, the procedure may be performed even in people taking anticoagulants without fear of  significant bleeding.

Advantages

The examination is relatively quick, informative and the investigated person is not exposed to any harmful radiation. In addition, there is no other commonly available method of examination of the neuromuscular transmission.