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Nerve Conduction Study – Electromyogram

EMG/NCS is a combined test consisting of nerve conduction study (NCS) measurements from various nerves according to the patient’s symptoms.  It may be followed, if necessary, by electromyogram (EMG) examination. 

Nerve Conduction Studies

Small electrical pulses are applied to the skin to stimulate the nerve below.  Measurements are made to calculate and compare the conduction velocity (speed) of different nerves.  Pulses feel like a sharp tingly/tapping sensation and some may cause brief muscle contractions.  Most patients find this electrical stimulation acceptable, and any discomfort is only brief. Nerves conduct at optimum velocity when warm so for results to be accurate, we need limbs to be warm.  

Important – STANDARD CARDIAC PACEMAKER – Nerve Conduction Studies use a small electrical current that can affect the function of a cardiac pacemaker.  Such appointments may take longer than usual to arrange, and necessitate liaison with Cardiology for the pacemaker settings to be modified for the duration of the test.

Important – DEFIBRILLATING PACEMAKER (ICD) – These appointments take longer to arrange and necessitate liaison with Cardiology to enable a cardiology physiologist can be present to modify the pacemaker settings and monitor the patient’s ECG throughout Neurophysiology testing.

Electromyogram Tests (EMG)

The EMG forms an additional investigation in about one in four patients in the Consultant Neurophysiologist’s EMG/NCS clinic and follows on from the NCS.  Most often, EMG is used to help diagnose symptoms such as pain or weakness in the muscles or numbness. It can establish whether muscle weakness is a result of a problem with the muscle itself (myopathy), or due to a neurological disorder. An examination including a combination of EMG and NCS can help determine whether the source of the problem is with a muscle, nerve or the neuromuscular junction (connection between a nerve fibre and its muscle).  
To carry out the EMG a very fine needle is inserted into a muscle to measure the naturally occurring electrical activity that happens when a muscle contracts.  The patient may be asked to move particular muscles for this to happen, and the physician will watch the muscle activity on a screen and listen to the sound through a speaker. Because the needle is very fine, discomfort is kept to a minimum.

Important – WARFARIN AND OTHER ANTICOAGULANTS – The EMG needle can cause bleeding in patients taking warfarin or clopidogrel to thin their blood.  In some cases this part of the investigation cannot be carried out.  To decide, further information is needed from both the patient and their referring doctor.  So before arriving for the EMG/NCS test, such patients should contact us so our consultant can decide how best to proceed.

Most Electromyogram/Nerve Conduction tests are carried out by a Consultant Neurophysiologist.  However, clinical physiologists perform nerve conduction studies in patients with unusual carpal tunnel symptoms or ulnar nerve problems at the elbow.  For a comprehensive assessment of more complex results, these patients are reviewed by the Consultant Neurophysiologist during the same appointment.