Electromyogram (EMG) & Nerve Conduction Study

What is an electromyogram (EMG)?

An electromyography (EMG) is a diagnostic procedure that records the electrical activity produced by the skeletal muscle to evaluate the function of nerves and muscles.

This test is used to diagnose neuromuscular disorders (conditions that affect the muscles or their nervous systems).

An EMG is frequently done together with a nerve conduction study (NCS). The NCS is used to detect nerve damage, which can lead to pain, tingling, or weakness in your muscles.

The results of these tests will help your doctor determine whether your condition is a muscular issue or a nerve issue.

How it works

Electromyography is based on the principle that nerve cells transmit small electrical signals from the brain to the muscles telling them to contract.

It consists of two tests: needle EMG and nerve conduction study.

Needle EMG

A needle EMG measures how well your muscles respond to the electrical signals.

During a needle EMG:

  • A needle connected to a computer is inserted into a muscle.
  • This needle reads muscle activity and sends the data to the computer.
  • The data (presented as a graph, sound or number) is interpreted by a specialist to evaluate how well the muscle works at rest and while moving.

Nerve conduction study

A nerve conduction study assesses the speed and strength of electrical activity in the nerves.

During a nerve conduction study:

  • Small monitoring discs (electrodes) are placed on the skin to sense and record nerve function.
  • A small current is then applied to the skin to see if your nerves can conduct it to the discs and complete the 'circuit'.
  • If there is anything wrong with the 'circuit' it could indicate some damage to the nerves.

Why do you need an EMG?

An electromyography is commonly performed if an examination suggests impaired muscle strength.

An EMG will help determine if muscle weakness is due to an injury of a nerve attached to the muscle, or if the weakness is caused by an underlying neurological disorder.

EMG and NCS testing can be done for conditions and procedures such as:

  • Myopathy
  • Motor neurone disease
  • Myasthenia gravis
  • Muscular dystrophy
  • Cervical or lumbar radiculopathy
  • Brachial or lumbar plexopathy
  • EMG guided Botox injection

What are the risks and complications of EMG?

Electromyography is a generally safe procedure and complications are rare.

Some uncommon but possible side effects of the procedure are:

  • Bleeding or bruising
  • Pain
  • Infection
  • Needle prick
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