Nerve conduction studies and EMG information sheet
Contact
EEG and Neurological Services, The Children's Hospital at Westmead
Phone: (02) 7825 2647
Location: EEG Department, Level 3, Banksia Building, The Children’s Hospital at Westmead
Introduction
The nerve conduction study (NCS) examines how a nerve works by measuring the speed at which a small electrical impulse travels along it.
The electromyography (EMG) study uses a tiny microphone inside a small needle to listen and record the sounds of the electrical activity within the muscle.
These two studies are usually done in the same appointment.
Purpose of the tests
These tests help diagnose medical conditions where the nerves or muscles are not be working properly.
Weakness, difficulty with walking, or a sensation of numbness or pins and needles may indicate nerve or muscle problems.
How the tests work
The nerve conduction study (NCS)
Preparing for the test
If your child is over the age of 12 months and having ‘laughing gas’ (Nitrous oxide), they should not eat or drink anything for two hours before the test. This is called fasting.
If your child is under 12 months of age they can eat and drink as usual.
Please dress your child in loose fitting clothing on the day, so the doctors can easily get to the skin above your child’s elbow and above the knee. All-in-one baby body suits, or onesies, are not suitable, and separate pants and tops are preferable.
Placing the electrodes
Small electrode dots are placed on the skin over a muscle which is supplied by a motor ‘moving’ nerve.
The electrodes are held in place with a temporary glue or paste and tape. The glue or paste washes off easily after the test.
In most cases, the nerve conduction study will be done on the arms and legs on one side of the body. Sometimes both sides of the body will be tested and compared.
During the test
Once the electrodes are attached, the nerve is stimulated with a small electrical impulse, or ‘buzz’. The response is recorded on a computer which calculates the speed of the impulse along the nerve.
The impulse often makes the muscles jerk and some children find this unpleasant or uncomfortable. The ‘laughing gas’ helps reduce these uncomfortable feelings.
We also test the sensory, or ‘feeling’ nerves. Generally, this test is less uncomfortable than the motor studies.
The test gives the doctor important information about how the nerve is working, and how the muscles respond to the electrical impulses directed through the nerve.
Finishing the test
When the test is over, the nurse will gradually reduce the amount of ‘laughing gas’. They will then give your child oxygen using a face mask for a few minutes to help them wake up fully.
Your child can eat and drink straight away. If your child feels sick in the tummy, it can help if they sip a drink slowly before they eat.
Test results
Please arrange an appointment with your doctor who will explain and discuss the results with you.
The electromyography (EMG) study
Preparing for the test
If your child is over the age of 12 months and having ‘laughing gas’ (Nitrous Oxide), they should not eat or drink anything for two hours before the test. This is called fasting.
If your child is under 12 months of age they can eat and drink as usual.
Please dress your child in loose fitting clothing on the day, so the doctors can easily get to the skin above your child’s elbow and above the knee. All-in-one baby body suits, or onesies, are not suitable, and separate pants and tops are preferable.
Inserting the needle
The doctor will gently insert a small needle into a muscle. The needle contains a tiny microphone to record the sounds the muscles make.
The nurse or doctor will use anaesthetic gel to numb the skin where the needle is inserted.
During the test
During the test, the muscle is relaxed and contracted to activate it.
The nurses might also reduce the ‘laughing gas’, or Nitrous Oxide, to make sure your child is alert and able to move their muscles.
The sound of the muscle activity may be quite loud especially when it contracts. We usually test only one or two muscles, but in some situations we may need to test several muscles.
Finishing the test
When the test is over, the nurse will gradually reduce the amount of ‘laughing gas’. They will then give your child oxygen using a face mask for a few minutes to help them wake up fully.
Your child can eat and drink straight away. If your child feels sick in the tummy, it can help if they sip a drink slowly before they eat.
Test results
Please arrange an appointment with your doctor who will explain and discuss the results with you.
Please remember: If your child is older than 12 months, they cannot eat or drink for 2 hours before these tests. This is called fasting.
If your child has not fasted, we will need to reschedule the test.
NCS and EMG safety
These tests can cause some mild pain or discomfort, but they do not harm your child.
For this reason, children over 12 months of age are given nitrous oxide or ‘laughing gas’ to help them relax during the test.
See the Nitrous Oxide factsheet for more information.