Dubai Neurology - Neurological Tests

 
 


 

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  Nerve Conduction Studies (NCS) & Electromyography (EMG)
 


Introduction:
 
If you are suspected of having a muscle or nerve disorder, your physician may request that you undergo nerve conduction studies and electromyography.  Although quite different data is obtained from each procedure, the information obtained from the two tests is complementary and assists your physician in reaching a diagnosis.
 
Who needs NCS/EMG studies
 
These studies are performed in order to investigate a variety of complaints including:
  • Numbness or tingling, especially in the arms or legs.
  • Pain in the extremities, neck or back.
  • Weakness that is thought to be due to disorders of peripheral nerves, the junction between muscles and nerves or muscles.
  • Muscle cramps or involuntary twitching.

Several disorders of the nervous system can be investigated with the help of these tests:

  • Radiculopathy (Such as in a herniated disc resulting in a pinched nerve in the neck or lower back)
  • Carpal tunnel syndrome (compression of a nerve at the wrist)
  • Low back pain
  • Neck pain
  • Neuropathy (such as with diabetic neuropathy)
  • Neuropathic pain (such as with painful diabetic neuropathy or post-herpetic neuralgia)
  • Myasthenia gravis (disorders of the neuromuscular junction)
  • Myopathies (such as muscular dystrophies)
  • Many other conditions






Where is the test performed?

This is an outpatient procedure.  The test may be performed in your physician’s office or in a hospital.

Who performs the test?

Electromyography is performed by a neurologist or neurophysiologist.  Physiatrists (physical medicine and rehabilitation physicians) may also perform this test.

Nerve conduction studies are also performed by neurologists or neurophysiologists, as well as by physiatrists.  In specialized centres, specially trained neurophysiology technicians may also perform this procedure.


How the test is performed?

Motor nerves carry information from the brain to the spinal cord and via peripheral nerves to muscles.  This is achieved via small electric impulses that ultimately result in movement.  Sensory information is carried from the body to the brain via sensory nerves by way of small electric impulses as well.

You will be asked to lie on an examination table or bed or in a reclining chair so that you are in a comfortable position and the areas to be tested are easily accessible.

In a motor nerve conduction study, electrodes (either flat metallic discs or adhesive strips) are placed on the skin over the muscle being tested while small electric currents are applied to the skin over the nerve that is supplying the muscle.  In a sensory nerve conduction study, ring electrodes are used to study the function of these nerves. 

The speed by which nerves transmit these electric impulses (conduction velocity) and the magnitude (amplitude) of the responses is recorded.  The information is transmitted to the recording apparatus and displayed on a computer monitor for interpretation by your physician. 

Electromyography involves inserting a tiny needle, with a microphone located at its tip, into various muscles in order to record activity both at rest and with movement.  The activity is heard via a speaker and displayed on the monitor for your physician to interpret. 

In many cases the examination will include areas far from where you are having symptoms because nerves can be very long.  Nerves and muscles on the other side of the body may at times be studied for comparison.


How long the test takes?

Nerve conduction studies are performed prior to an EMG if both tests are being done.  Nerve conduction studies take anywhere from 30 minutes to 90 minutes depending on the clinical scenario.  An EMG may take from 15 to 45 minutes.

How do I prepare for this test?
  • Wear loose-fitting clothing in order to allow your examiner adequate access to the areas that are to be tested. You may be asked to wear a hospital gown
  • Do not use any creams, lotions, moisturizers or powders on the day of the test. It is preferable to shower prior to this procedure although this is not a must
  • Avoid caffeine and nicotine for at least three hours before the test
  • Inform your physician if you have any bleeding disorder or if you are taking any blood thinners
  • Inform your physician if you have a pacemaker

How the test will feel?

In general, both nerve conduction studies and electromyography are associated with a mild degree of discomfort.  Closing your eyes, relaxing your body and imagining that you are in a quiet and pleasant environment usually helps in significantly lessening the discomfort.  Some patients fall asleep during the procedure. 

In nerve conduction studies, you will feel a brief, uncomfortable tingling sensation and a muscle twitch each time the electric pulse is applied.  This is transient and results in no harm whatsoever since the strength of the current is far below the threshold of causing any damage.

In an electromyographic study, you will feel a brief transient sharp sensation when the needle pierces the skin.  As the needle settles in the muscle, there is minimal discomfort.  Sometimes when your physician moves the needle, a painful sensation is elicited in a sensitive part of the muscle.  This can be relieved by moving the needle slightly once you alert your physician to your discomfort.  In some cases, tenderness or tingling may persist for up to 2 days in the areas tested.


Other issues:

An EMG needle causes a mild degree of trauma to the muscle. This is not clinically significant. However, certain enzymes (CK, AST and LDH) in the blood may become elevated as a result of this procedure and it is therefore preferable not to have blood tests for about 10 days after the procedure since the results may be falsely elevated. It is also preferable not to take a biopsy from a muscle that was recently tested since this too may give inaccurate results.

 


 
  Neurological Tests

Electroencephalogram Brain wave test (EEG)
Nerve Conduction Studies (NCS) & Electromyography (EMG)
Evoked Potentials
Carotid Ultrasound
Computerized Axial Tomography (CT Scan / CAT Scan)
Magnetic Resonance Imaging (MRI)
Lumbar Puncture
Angiography
© 2006 D M Kayed, MD, FAAN Dubai Neurology
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