EMG NCS Test
(Electromyogram and Nerve Conduction Study)
Your Doctor has ordered an Electromyography (EMG)?
Your doctor has ordered an EMG/NCS to assist in making a more specific diagnosis. Like most diagnostic tests, the results are carefully reviewed and analyzed along with a thorough history and physical exam, x-rays, MRI/CT scans and other studies. In other words, these studies are an extension of the clinical evaluation by your doctor. At the Pain Prevention and Rehabilitation Center (PP&R), Dr. Suthar (board-certified physical medicine and rehabilitation) uses a state-of-the-art computerized EMG/NCS machine to perform this diagnostic test. This handout was designed to help you understand the test and reduce unnecessary anxiety.
What is a Nerve Conduction Study (NCS)?
Nerve conduction studies are performed by stimulating a peripheral nerve and recording the reaction. Nerve conduction studies are performed on either sensory nerves (nerves that provide sensation) or mixed sensorimotor nerves (nerves going to muscles).
Why is a Nerve Conduction Study ordered?
The study is usually ordered to determine if there is or is not a neurologic deficit. Examples include nerve entrapment neuropathy (i.e. carpal tunnel syndrome), polyneuropathy (generalized nerve disease), or trauma-related nerve injuries. The study can also distinguish between nerve and muscle disorders, the severity and extent of the disease, and help categorize the type of injury. At the PP&R clinic, this study is most often ordered to evaluate the possibility of sciatica (a pinched nerve at the level of the spine) versus a peripheral nerve injury such as carpal tunnel syndrome.
How will I feel?
Most patients describe a mild electric current similar to a TENS unit or electrical-stimulation unit. Others describe a sensation similar to “hitting the funny bone”. Regardless of the feeling, the sensation lasts only microseconds. Sometimes when a mixed nerve is stimulated, a reflex in the corresponding muscle briefly occurs. There is no long-term discomfort associated with NCS.
Are there any precautions or concerns?
There are no known risks or dangers of NCS. NCS is safe and well tolerated in most patients. However, you need to tell us if you have a cardiac pacemaker. Sometimes pacemakers are effected by the electrical current. We also need to know if you have an indwelling catheter (i.e. Swan-ganz or central venous line).
What is Electromyography (EMG)?
Electromyography is a diagnostic test that involves the placement of micro-needles into different muscles to measure electrical activity and assess physiologic function. The electrical activity of muscles can be detected by skin electrodes, amplified and displayed on a monitor. Unlike NCS, EMG does not involve external electrical stimulation. Nevertheless, EMG studies are often part of the overall examination, which includes NCS.
What does an EMG determine?
EMG is performed for a variety of clinical situations. EMG evaluation is used to determine primary muscle disease (myopathies, muscular dystrophy, SLE, alcoholic myopathies, etc.), nervous system disorders (radiculopathy, peripheral nerve injury), and neuromuscular disorders (myasthenia gravis). There are other disorders EMG can help detect including polio, tumors, ALS, etc. In most cases, at the end of the examination, Dr.Suthar will analyze and formulate a preliminary diagnostic impression.
Is EMG a treatment?
No. EMG is primarily a test to assess both the nerves and muscles. Although the needles used are as small as acupuncture needles, most patients usually don’t experience symptom reduction.
Are there any precautions or concerns?
Local discomfort at the site of needle insertion is common. This is often mild in severity and has no long-term discomfort. It is often recommended that you stop taking aspirin 5-7 days prior; NSAID should be stopped 3 days prior.
How is EMG performed?
You will lie flat on the exam table. No sedative or pain medications are needed. The area will be cleansed thoroughly with alcohol pads. If is helpful if you will try to relax as much as possible. Micro-needles are then placed into different muscles. Several muscles are tested individually. The EMG monitor will amplify the electrical sound activity of the muscles.
What will I feel?
Needle examination is, by nature, a slow and labor-intensive process. The duration of the needle examination is brief and once the skin is penetrated it often is not felt. Remember that you are always in control and rest breaks can be taken if necessary.
Where does this test take place?
At the PP&R, the test is performed in an exam room. Some parts of the exam are done while you are in a sitting position. The EMG/NCS machine looks like a desktop computer, but has extra input ports for wires and a more sophisticated monitor.
How long does the test take?
Overall, the entire study may take 45 minutes to an hour. The actual time anything is felt is usually microseconds for the NCS and just seconds in the EMG part. Sometimes the study takes longer if additional questions are to be evaluated.