Electromyography (electromyography; EMG) is a technical examination procedure for measuring electrical muscle activity. It is used to assess muscle function by measuring the electrical activity of a muscle during rest and movement.
Indications (areas of application)
- Muscle weakness – to differentiate between muscle disease, such as muscular dystrophy, or disease of the responsible nerve, such as diabetic neuropathy (diseases of the peripheral nervous system) or viral (“virus-related”) neuropathy (herpes simplex virus types 1 and 2, varicella zoster virus causing herpes zoster, cytomegalovirus and Epstein-Barr virus causing mononucleosis).
- Injury or inflammation of a nerve resulting in muscle paralysis – to predict whether the nerve will regrow (reinnervation) or not
- Numbness in neuropathies such as diabetic neuropathy.
- Disc hernia (herniated disc)
- Entrappment syndromes – such as carpal tunnel syndrome, tarsal tunnel syndrome or even nerve damage due to spondylosis of the cervical spine (C-spine).
The procedure
The doctor sticks a thin needle electrode directly into the muscle to be examined (needle EMG). In this way, the activity of individual muscle fibers inside a muscle can be derived via an amplifier. The measured voltage fluctuations are displayed and stored by means of computer analysis and made audible via loudspeakers in the form of noise and rattling.When analyzing the EMG, attention is paid to:
- Electrical signals generated during needle insertion.
- The form of spontaneous signals when the muscle is relaxed.
- Signals that occur when the patient gently tenses the muscle during the examination.
A relaxed muscle normally shows no electrical activity. However, when it contracts only slightly, electrical activity already occurs, which increases with stronger muscle movements.Electromyography is used to classify the nature and severity of various muscle and nerve disorders. It is possible to determine which muscle groups, or in the case of larger muscles, which muscle fiber groups, are affected. Furthermore, it can be determined which nerves are affected and to what degree, as well as the extent of any pathological nerve changes.