What is an EMG or nerve conduction test?

What is an EMG or nerve conduction test?

This is a routine test performed in specialist hospitals.

The EMG (electromyography) records the electrical messages that muscles produce. The nerve conduction test measures the speed at which the messages travel along a nerve. These tests help us to work out how well your child’s nerves and muscles are working. Together they are often called an EMG test and may include one or both of the above techniques.

What does EMG stand for?

EMG stands for electromyography.

• Electro – the electrical impulses we are measuring
• Myo – muscle
• Graphy – the way the results are presented

How long will we be at the hospital?

Your appointment with the consultant will last about an hour. Whilst we try to keep to appointment times, very occasionally there can be a delay.

How do EMG or nerve conduction tests work?

Nerve conduction tests

Nerve conduction tests record how fast nerves send messages to the brain and back. We send messages to the nerves using pads or rings placed on the surface of your child’s skin. We can then record how fast the message travels to another point where it is recorded using pads placed on the skin. This tells us how fast the nerve is working.

EMG tests

This studies the electrical activity in the muscles. The EMG is recorded using a fine needle electrode inserted into the muscle, which produces a short pinprick sensation. Younger children are offered the option to attend early so that anaesthetic cream may be applied. We also have a coolant spray which may be used to numb the area during the test. Once the needle is in place the activity in the muscle can be observed at rest and then whilst being used.

During the nerve conduction test we send messages to the nerves and they will feel a tapping/tingling sensation. Most children do not find this too uncomfortable. Staff are experienced in comforting anxious children and children with sensory or special needs.

How will the test help them?

The measurements we take help us to find out whether your child has any trapped or damaged nerves. It can also investigate a wide range of nerve and muscle disorders. The results from the tests can help your child’s consultant to provide the right treatment for them.

Where will the test be done?

The test is performed in a recording room on E Floor, Grey Stair/Lifts, at Sheffield Children’s Hospital, S10 2TH.

The nearest entrance to the department is on Damer Street around the corner from the Emergency Department. Then follow the signs to grey lifts or stairs and travel to E floor and report to reception. You can also follow the signs for Grey lifts from the Main Entrance.

Public transport is the best way to travel to Sheffield Children’s Hospital. We are well served by bus services (51, 52, 273, 274, 275) and close to the tram route. Find out more on our public transport webpage: www.sheffieldchildrens.nhs.uk/patients-and-parents/public-transport

Please allow plenty of time for delays and roadworks. For up-to-date parking information visit our webpage on parking:
www.sheffieldchildrens.nhs.uk/parking

Parents and carers – please note

We have no provision for accompanying children to be supervised whilst your child is having the EMG. If you have any problems arranging childcare, please ring the department to discuss this. 0114 271 2129

Is there anything we need to do before the test?

Before you have the test, you should make sure your child:

• Removes any jewellery as this makes it easier for us to attach the electrodes. Leaving jewellery at home is also safer.
• Wears clothing with short sleeves or loose clothing such as loose trousers or a skirt, as this will make it easier if we need to look at their legs or arms.
• Avoids using lotions and creams on their skin before the test as it makes it difficult for us to attach the electrodes.
• Eats and takes any medication as normal.

What happens before the test?

On the day of your child’s test, we will take them into the room where the test will be done. We will make them comfortable in an appropriate position on a couch, in their pushchair or on your knee. If their hands or feet are cold then we will put them in warm water. This is because if they are cool it can affect the results. At this time you will be able to ask any questions you have.

What happens during the test?

There are 3 parts to the test and these are described below. Your child may not need all 3. It depends on the clinical problem and the doctor’s findings during the test.

Part 1 – sensory nerve testing

During the test they will need to stay as still and relaxed as possible. First we clean the skin with an alcohol wipe. This improves contact between their skin and the rings or pads which gives better results. Then the nerves supplying sensation are tested using rings on the fingers or buttons on other parts of the body. For a short time they will feel a repetitive tapping or tingling sensation.

We will also measure between the electrodes using a tape measure and a marker pen. This means small dots are made on the skin but these will wash off. The test checks the sensory nerves for any delays in sending messages along your child’s limbs.

Part 2 – motor nerve testing

This part of the test allows us to check the nerve supply to the muscles. Your child will feel a tapping or tingling sensation similar to that felt during part 1, this time it sends a message to the muscle. The muscle we are testing gives a small twitch. Then we will mark points and take measurements. Any delays in the message being sent can give valuable information to the doctor about the nerve supply.

Part 3 – EMG testing

To look at the EMG signals, we will need to insert a small needle into the muscles to be tested. The needle we use is for single use and is disposed of after each child. It is designed to carry a very fine recording wire.

The doctor will examine the electrical activity whilst the muscle is at rest. During the next part of the test we will ask your child to use their muscles, so that we can observe their pattern of activity. The activity is displayed on a screen and can be heard on a speaker as a crackling sound. We may repeat the test for different muscles. This activity helps the doctor to decide whether the problem is a disorder affecting the nerve supply to the muscle or a disorder of the muscle itself. This is very important when making a diagnosis.

Is having a nerve conduction or EMG study safe?

• If the coolant spray is used to numb an area for needle EMG there is a very small risk of a cold skin burn (frostbite).
• If your child has any implanted device such as cardiac pacemaker, deepbrain stimulator, then please tell the health care assistant and the doctor before you have the test. You can still have the test but we need to modify the position of the electrodes slightly, if at all.
• If your child has ever received botulinum toxin injections, please tell us when you ring to make your appointment.
• If your child is taking anticoagulant (blood thinning) treatment, for example warfarin, or rivaroxaban or other equivalent tablets, please tell us when you ring to make your appointment. They can still have the nerve conduction part of the test but we may not perform the EMG or we may seek further information. Needle EMG when on anti-coagulants may result in some bleeding within the muscle which can be painful. If the bleeding is severe, it can cause swelling in the muscle which in certain muscles can result in a potentially severe condition called compartment syndrome. This may require admission for medical or surgical treatment. This is very rare and occurs in less than 1 in every 10,000 patients with bleeding disorders.
• Only if your child is having needle EMG studies in certain muscles for problems around the shoulders, chest or abdomen areas, there is a risk of the needle puncturing the chest wall. This allows air to enter the cavity which surrounds the lungs (called a pneumothorax).The risk of this happening is 1 in every 200-500 patients. If this happens it can cause the lung to collapse and the patient may experience no symptoms or they may have shortness of breath and chest pains which may require admission to a hospital ward.

When will we get the results?

You will not get the results on the same day because we will need to make further measurements and analysis. The consultant who referred your child for the test will be sent a report by post within 5 working days.