Electromyography (EMG) of the diaphragm muscle

Introduction

This leaflet is designed to give you information about the EMG (electromyography) investigation for which you have been referred. Specifically, it is about the risks of studying your diaphragm with needle EMG. We hope it reassures and informs you. You will have the opportunity to discuss this further with the doctor performing the test, and your consent will be sought before any examination takes place.

Why am I being referred for this test?

The diaphragm is one of the main muscles that power respiration (breathing). If this muscle is weak for any reason it tends to cause shortness of breath, sometimes worse when lying down. Electromyography (EMG) of the muscle allows us to investigate the muscle, and the nerve that supplies it (the phrenic nerve), and can help with diagnosis, and therefore management, of some breathing problems.

Is there another way of studying this muscle?

Scans, such as ultrasound, can show the muscle, but they do not provide information about the nerve supplying the muscle. Surface EMG recordings do not provide detailed information about the nerve either.

What are the benefits of having this test performed?

It provides more detailed information about the diaphragm muscle, and the nerve supply to it. This can help the doctors looking after you reach a more accurate diagnosis about your breathing problems, and therefore a more accurate management plan.

What if I choose not to have the EMG test of this muscle?

You are of course free to choose what tests you undergo, and you may choose not to undergo EMG of the diaphragm. We can still perform EMG of other muscles if this is clinically indicated, and if you are in agreement. Other muscles can be examined without the same risk of pneumothorax (collapsed lung) since they are not as close to the lung (see below section on risks). Of course if the diaphragm muscle has not been studied your referring doctors will not have as much diagnostic information, but the importance of this varies in different clinical settings and will be discussed by the doctor who will be performing the EMG.

What happens before the investigation?

There are no special preparations required. You can eat and drink normally, and there are no driving restrictions.

Please inform the examining doctor about the following

1. If you are taking blood thinning medications such as warfarin, apixaban, rivaroxaban
2. If you have an increased risk of bleeding or infection
3. If you have an implanted cardiac defibrillator

How is EMG of the diaphragm performed?

There is more than one way in which the diaphragm muscle can be studied by EMG. This will be discussed by your doctor performing the procedure. It is generally carried out using a very thin EMG needle inserted towards the lower end of your rib cage. It is a very quick procedure, and usually takes just a few minutes. It is generally performed with the help of ultrasound (performed by a radiologist) to ensure the needle is in the correct muscle and to minimise the risk of complications (see below)

What are the risks involved?

Research studies of the risks of EMG of the diaphragm muscle show there is up to a 1 in 500 risk of causing a pneumothorax (punctured lung). This is because the muscle lies close to the ribs and the lung. If this were to occur you would need to attend hospital for a chest X-ray, and you may need a chest drain to re-inflate the lung. This is discussed further below. We have an experienced team of doctors, used to conducting this examination. To minimise the chance of this complication the needle is inserted at a site that is safest for the lung and ultrasound is used to monitor the needle position.

EMG is overall a very safe procedure. The needle is very fine (thinner than a blood needle, rather more like an acupuncture needle), and it is only used once, so cannot transmit infections between patients. After needle EMG the muscle may itch, or feel slightly achy, for a few minutes. Occasionally you will notice a small bruise, but significant complications due to bleeding are very rare (less than 1 in 10,000). We may limit the EMG examination in some situations, for example if you are taking blood thinning medications.

What do I do after the test?

If you are an outpatient you will be asked to wait for 30 minutes to ensure you feel well and do not develop symptoms. After this you may go home, with this information sheet to refer to if needed. If you are an inpatient the ward team will monitor you after the procedure.

What do I look out for?

In the unlikely event that you were to develop a pneumothorax (punctured lung) after EMG, this would cause symptoms of chest pain and shortness of breath. If this were to occur it generally does so soon after the EMG examination (within hours, up to 48h).

What do I do if there is a problem?

If you experience chest pain or shortness of breath within 48h of the study you will need to attend your local Accident and Emergency department to have a chest X-ray, which can diagnose a punctured lung (pneumothorax), and arrange treatment if required. You are advised to take this leaflet with you to show to the doctors there. We would also be grateful if you could inform us of any problems in due course, using the contact details below, but this does not need to be done rapidly, and it can be done after you have visited the Emergency Department.

When do I get the results of EMG?

The results of your investigation are sent to the referring clinician within a couple of days. It is often possible to discuss preliminary results at the time of testing. However, in many instances the overall interpretation of results needs to be performed by the clinician who referred you for the test.

My Chart

We would encourage you to sign up for MyChart. This is the electronic patient portal at Cambridge University Hospitals that enables patients to securely access parts of their health record held within the hospital’s electronic patient record system (Epic). It is available via your home computer or mobile device

More information is available on our website: My Chart

Contacts/Further information

If you have any questions or concerns before attending for this appointment, please ring us on 01223 216738 or 01223 348290. The department is open Monday-Friday 08.30-17.00. There is a voicemail service to leave a message if we are unavailable.

References/ Sources of evidence

Gechev A, Kane NM, Koltzenburg M, Rao DG, Van de Star R. Potential risks of iatrogenic complications of nerve conduction studies (NCS) and electromyography (EMG). Clinical Neurophysiology Practice 1 (2016) 62-66.

Bolton CF (1993) AAEM minimonograph #40: clinical neurophysiology of the respiratory system. Muscle Nerve 16:809-818.