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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
How do you prepare for EMG?
Before electromyography, your doctor will review your medical history.
On the day of the test:
Bathe beforehand
Avoid using any creams, lotions or fragrance
Wear loose-fitting, comfortable attire
Depending on your medical condition, your doctor will recommend specific preparation for the test.
Inform your doctor if you:
Are taking any herbal supplements or medication, including aspirin or blood thinners
Have a blood disorder such as haemophilia that can increase the risk of prolonged bleeding, so doctor can precautions to minimise bleeding
What can you expect in an EMG?
Fasting is not generally required prior to the procedure.
Before the procedure
To prepare you for an electromyogram, you will be need to remove all jewellery, spectacles, hair pins and other metal objects on your body. This is to prevent any interference.
During the procedure
During the procedure, you will be sitting or lying down.
After confirming the site to be examined, the skin will be cleaned with antiseptic.
A ground electrode will be placed on your body, usually under an arm or leg.
Your doctor will insert a tiny needle with an electrode is inserted into the muscle tissue to allow the electrical activity of the muscle to be recorded.
The results allow the neurologist to diagnose any abnormal muscle or nerve activity. This test helps to differentiate between nerve root and muscle disease.
Care and recovery after an EMG
You may experience some muscle soreness after an electromyogram. This usually goes away in a day or two.
Some bruising may able appear where the needles were inserted.
If the muscle soreness does becomes worse, or if there bleeding, is inflammation, a sore or pus present where the needles were inserted, do seek medical advice.
