What Are Electromyography (EMG) and Nerve Conduction Studies (NCS)?
An electromyogram (EMG) measures the electrical activity of muscles at rest and during contraction. Nerve Conduction Studies measure how well and how fast the nerves can send electrical signals. These diagnostic tests help in the diagnosis of conditions or diseases affecting the peripheral nerves and muscles.
General Indications for EMG & NCS are:
Numbness, tingling, burning sensation, limb pain (arm or leg), muscle weakness, and/or atrophy.
EMG & NCS Studies Assist in the Diagnosis of:
- Facial nerve palsy
- Carpal tunnel syndrome
- Cubital tunnel syndrome (ulnar nerve entrapment at elbow)
- Tarsal tunnel syndrome (plantar nerve entrapment at ankle)
- Nerve injuries
- Herniated disc
- Peripheral neuropathy such as diabetic neuropathy
- Radiculopathy – cervical, thoracic and/or lumbar
- Brachial and lumbar plexus injury
- Guillain Barre syndrome
- Congenital and acquired neuropathies
- Myopathies such as muscular dystrophy
- Neuromuscular junction disorders such as myasthenia gravis
- Motor neuron diseases such as amyotrophic lateral sclerosis (ALS)
How do you prepare for an EMG & NCS?
There is minimal preparation required on the part of the patient for an EMG & NCS.
- Wear loose-fitting clothing for comfort and convenience. You may be given a hospital gown to wear.
- Be sure to tell your physician about any medications that you are taking, specifically aspirin, blood-thinners (i.e. Coumadin/Warfarin). The doctor will advise you when/if to cease such medications prior to testing.
If you have a bleeding disorders or an implanted electrical device (i.e. a pacemaker) and/or a stimulator, the physician needs to be advised in advance. As always, report any allergies.
What to Expect…
The skin over the area(s) to be tested is cleaned. A needle electrode that is attached by wires to a recording machine is inserted into your muscle(s).
When the electrodes are in place, the electrical activity in that muscle is recorded while the muscle is at rest. Then the technologist or the doctor will then ask you to tighten (contract) the muscle slowly and steadily. This electrical activity is recorded. The electrodes will be moved a number of times to record the activity in different areas of the muscle or in different muscles.
The electrical activity in the muscle will appear as wavy and spiky lines on a video monitor and this activity is then reviewed and analyzed.
An EMG may take 20 to 60 minutes.
During an EMG test, you may feel a quick, sharp pain when the needle electrode is put into a muscle. After the test, you may be sore and have a tingling feeling in your muscles a few hours. In addition, there may be some bruising. If your pain gets worse or you have swelling, tenderness, or pus at any of the needle sites, call your doctor.
Nerve conduction studies (NCS)
In this test, several flat metal disc electrodes are attached to your skin with tape. A shock-emitting electrode is placed directly over the nerve, and a recording electrode is placed over the muscles controlled by that nerve. Several quick electrical pulses are given to the nerve, and the time it takes for the muscle to contract in response to the electrical pulse is recorded. The speed of the response is called the conduction velocity. The same nerves on the other side of the body may be studied for comparison. When the test is done, the electrodes are removed.
Nerve conduction studies are done before an EMG if both tests are being performed. Nerve conduction tests may take from 15 minutes to 1 hour or more, depending on how many nerves and muscles are studied.