What is electromyography?
An electromyography (EMG) is a diagnostic test to analyze the health of muscles and the nerve cells (neurons) that control them by analyzing electrical activity in the muscles.
What does electromyography consist of/what does it involve?
Electromyography consists of two parts: a nerve conduction study and a needle EMG.
The nerve conduction study involves placing electrodes on the skin in the area that has been experiencing symptoms. These measure the speed and strength of electrical signals between different points to assess how well motor neurons communicate with muscles.
In needle EMG, electrodes are inserted into the muscle through a needle. These assess the electrical activity within the muscle tissue both when the muscle is contracted and at rest. Once the test is completed, the electrodes are removed.
The electrode readings are sent to a computer, which displays them in the form of graphs and/or numerical values, which can be interpreted by the physician.
Why is electromyography performed?
Electromyography is used to diagnose or rule out a number of conditions affecting the nerves and/or muscles. A physician may order an EMG if the patient has the following symptoms:
- Muscle weakness.
- Tingling.
- numbness
- cramping
- paralysis
- pain in the extremities
- Involuntary twitching (tics).
How to feel/what to expect during the test
You may be asked to lie down or sit up during electromyography. Before the needle EMG, the doctor will clean the area where the needle is to be inserted with an antiseptic. You may feel some pain or discomfort when the needle is inserted.
What do abnormal results mean?
If electromyography produces abnormal results, it could indicate:
- Muscle disorders, e.g. muscular dystrophy, polymyositis.
- Disorders affecting the connection between the motor neuron and the muscle, e.g. myasthenia gravis.
- Peripheral nerve disorders (nerves outside the spinal cord), e.g. carpal tunnel syndrome, peripheral neuropathy.
- Conditions that damage motor neurons in the spinal cord or brain, such as poliomyelitis or amyotrophic lateral sclerosis (ALS).
- Conditions that damage the nerve root, e.g., spinal disc herniation.