EMG; Types, Indications/Uses, Procedures, Results

EMG
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EMG (Electromyography) is an electrodiagnostic medicine technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyograph detects the electric potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect medical abnormalities, activation level, or recruitment order, or to analyze the biomechanics of human or animal movement.

Types of EMG

1. According to Wikipedia, there are two kinds of EMG

  • Surface EMG
  • Intramuscular EMG

2. According to the link provided below, EMG can be classified as

  • Clinical (or diagnostic) EMG
  • Kinesiological EMG
Kinesiological EMG is also used in clinical practice during clinical gait analysis, I’m not sure how this differentiation would be appropriate.

3. According to the complexity of the patient’s problem,

  A.  EMG and nerve conduction studies (NCS) only

This type of assessment is appropriate for straightforward cases of the carpal tunnel syndrome, ulnar neuropathies at the elbow or common radiculopathies, or where the patient has already had a neurological assessment and where the clinical information from this assessment is provided along with the requisition with a specific question to be answered by diagnostic EMG/NCS testing.

The testing for this type of assessment would include

  • A brief clinical assessment.
  • The appropriate NCS and EMG done to answer the question.
  • A discussion of the test results with the patient by the EMG physician.

This type of assessment would usually take from 30 to 60 minutes, but can take up to 2 hours or more for more complex problems. A full report of the electrophysiological studies will be sent to the referring physician, usually within 10 to 14 days. Any further investigations, referrals or treatment will be left to the referring physician.

B. EMG and NCS with limited consult

This type of assessment is strongly suggested for more complex situations including a patient with a brachial or lumbosacral plexopathy, a complicated entrapment neuropathy or radiculopathy, some peripheral neuropathies or myopathies. Suggestions regarding further investigations or therapy will be offered and the referring physician will follow the patient and supervise treatment afterwards. This type of assessment is also suggested for more “simple” problems if additional clinical input is desired beyond providing the results of electrodiagnostic testing.

This type of assessment includes

  • A specific clinical assessment relevant to the referring problem.
  • EMG/NCS studies done depending on the clinical assessment, at the discretion of the assessing EMG physician.
  • A correlation of the electrodiagnostic results with the clinical assessment is provided, as well as suggestions for further investigations and treatment of the specific referring problem as appropriate.
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This type of assessment generally takes from 60 to 90 minutes, longer for more complex problems. The results and suggestions are sent back to the referring physician within 10 to 14 days. Long term follow-up of the patient is left to the referring physician.

C.  EMG/NCS and Full Consult

This type of assessment is strongly recommended for multi-system disorders with both central and peripheral nervous system involvement. It is also suggested for complicated neuromuscular conditions including plexopathies, peripheral neuropathies, myopathies and disorders of neuromuscular transmission where the patient is to be followed by the EMG physician for other investigations, treatment and clinical follow-up. This assessment is also useful for more “simple” problems if additional clinical input and treatment suggestions are desired.

This assessment consists of

  • A complete neurological assessment.
  • EMG/NCS studies done based on the clinical assessment.
  • A correlation of the results of EMG/NCS with the clinical assessment is provided, as well as suggestions for further investigations and treatment as appropriate. Suggestions regarding other neurological problems are also offered if appropriate.
  • The follow-up and supervision of the patient for subsequent investigations and treatment will be arranged by the assessing EMG physician as appropriate.

This type of assessment takes from 1 – 2 hours. The results and suggestions will be sent out within 10 to 14 days.

4.  According to the testing instruments

  • Needle EMG

For this test, a small, thin needle is inserted into several muscles to see if there are any problems. It is used once for each patient and is thrown away after the test. There may be a small amount of pain during this part of the examination. The doctor tests only the muscles necessary to decide what is wrong. During the EMG test the doctor will be able to hear and see how your muscles and nerves are working by the electrical signals made by your muscles. The doctor then uses his medical knowledge to figure out what could be causing your problem.

  • Nerve conduction studies

Nerve conduction studies show how well the body’s electrical  signals are traveling to a nerve. This is done by applying small electrical shocks to the nerve and recording how the nerve works. These shocks cause a quick, mild, tingling feeling. The doctor may test several nerves.

  • Evoked potentials

Evoked potentials are painless tests that check the nerve pathways through the spinal cord or from the eyes and ears. The signals for these tests can come from small electrical shocks, light pulses, or clicks of sound in the ears. The nerve responses are recorded over the scalp and other areas of skin.

  • Muscle Biopsy

A muscle biopsy is a procedure used to diagnose diseases involving muscle tissue. Tissue and cells from a specific muscle are removed and viewed microscopically. The procedure requires only a small piece of tissue to be removed from the designated muscle. The information these tests provide helps determine exactly what disease and what form of it the person has. Watch the video for more information.

  • Ischemic exercise test

The Forearm Ischemic Exercise Test is useful in the differential diagnosis of metabolic causes of muscle weakness, fatigue, and cramps. The test consists of a series of blood draws taken from the arm, both while the arm is at rest, and after exercising it while wearing a blood pressure cuff. Changes in blood chemistry between blood draws detect metabolism problems in the muscle. Watch the video for more information.

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Indications/Uses of EMG

EMG can help diagnose many muscle and nerve disorders, including
  • Muscular dystrophy
  • Congenital myopathies
  • Mitochondrial myopathies
  • Metabolic myopathies
  • Myotonias
  • Peripheral neuropathies
  • Radiculopathies
  • Nerve lesions
  • Amyotrophic lateral sclerosis
  • Polio
  • Spinal muscular atrophy
  • Guillain-Barré syndrome
  • ataxias
  • Muscular dystrophies
  • Duchenne Muscular Dystrophy
  • Becker muscular dystrophy
  • Facioscapulohumeral dystrophy
  • Limb girdle muscular dystrophy
  • Centronuclear myopathy
  • Myotonic dystrophy
  • Mitochondrial myopathies
  • Muscular dystrophies
  • Becker muscular dystrophy
  • Facioscapulohumeral dystrophy
  • Limb girdle muscular dystrophy
  • Centronuclear myopathy
  • Myotonic dystrophy
  • Mitochondrial myopathies
  • Myasthenia Gravis
  • Lambert–Eaton myasthenic syndrome
  • Botulism poisoning
  • Organophosphate poisoning
  • Hypermagnesemia
  • Hypocalcemia
  • myasthenias
  • Inflammatory myopathies
  • Polymyositis
  • Dermatomyositis
  • Inclusion body myopathy
  • Myotonia Congenita

General Compain of Patients of EMG

Some symptoms that may call for an EMG include

The results of an EMG can help your doctor determine the underlying cause of these symptoms. Possible causes could include

  • Muscle disorders, such as muscular dystrophy
  • Disorders that affect the ability of the motor neuron to send electrical signals to the muscle, such as myasthenia gravis
  • Radiculopathies
  • Peripheral nerve disorders that affect the nerves outside the spinal cord, such as carpal tunnel syndrome
  • Nerve disorders, such as amyotrophic lateral sclerosis (ALS)

Before the procedure of EMG

  • Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
  • Generally, fasting is not required before the test. In some cases, cigarettes and caffeinated beverages, such as coffee, tea, and cola may be restricted two to three hours before testing.
  • Notify your doctor of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.
  • Notify your doctor if you have a pacemaker.
  • Dress in clothes that permit access to the area to be tested or that are easily removed.
  • Stop using lotions or oils on your skin for a few days before your procedure, or at least stop using them on the day of the exam.
  • Based on your medical condition, your doctor may request other specific preparation.

Generally, an EMG procedure follows this process

  • You will be asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or other metal objects that may interfere with the procedure.If you are asked to remove clothing, you will be given a gown to wear.
  • You will be asked to sit or lie down for the test.
  • A neurologist will locate the muscle(s) to be studied.
  • The skin will be cleansed with an antiseptic solution. Next, a fine, sterile needle will be inserted into the muscle. A ground electrode will be positioned under your arm or leg.
  • Five or more needle insertions may be necessary for the test. You may experience slight pain with the insertion of the electrode, but it is usually painless.
  • If the test is painful you must tell your examiner because this can interfere with the results.
  • You will be asked to relax and then perform slight or full-strength muscle contractions.
  • The electrical activity from your working muscle will be measured and displayed on the oscilloscope.
  • An audio amplifier may also be used so that both the appearance and sound of the electrical potentials can be evaluated. If the recorder is attached to an audio amplifier, you may hear a sound like hail on a tin roof when you contract your muscle.
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Results of EMG

Findings of Nerve Conduction Studies and EMG in Carpal Tunnel Syndrome(Open Table in a new window)

Severity of Carpal Tunnel Sensory Nerve Action Potential Compound Motor Action Potential Needle EMG Activity
Mild Prolonged latency Normal Normal
Moderate Prolonged latency and decreased amplitude Prolonged latency Normal
Severe Absent Prolonged latency and decreased amplitude Abnormal activity

Table 2. Common Disorders (Open Table in a new window)

Disorder Distal Motor Latency Distal Sensory Latency Conduction Velocity Amplitude of the Evoked Response
Motor neuron disease Normal Normal Normal Reduced
Axonal polyneuropathy Normal Normal Slight decrease Reduced
Demyelinating polyneuropathy Prolonged Prolonged Decreased Normal
Entrapment neuropathy Normal (may be prolonged if this is a distal entrapment such as carpal tunnel syndrome) Normal (May be prolonged if this is a distal entrapment such as carpal tunnel syndrome) Decreased at the entrapment region May be decreased when stimulating proximal to the site of entrapment
Radiculopathy Normal Normal Normal Motor response may be decreased
Myopathies Normal Normal Normal Decreased motor amplitude

Things to know about an EMG 

  • Patients have both NCS and needle examination when an EMG is ordered.
  • The length of stay is 1 to 3 hours, based on the clinical problem, for both parts of the test at all EMG sites. Please plan to stay accordingly.

Precautions: If any of the following precautions apply,

  • You have had symptoms for less than three weeks.
  • You are taking medications such as:
    • Mestinon (pyridostigmine bromide)
    • Coumadin (crystalline warfarin sodium)
    • Lovenox (enoxaparin)
    • Heparin
    • Xarelto (rivaroxaban)
    • Eliquis (apixaban)
    • Pradaxa (dabigatran)
  • You have any bleeding disorder.
  • You have any electrical internal devices implanted (defibrillators, internal pain stimulators, deep brain stimulators, etc.).
  • The patient is a child who needs sedation for the procedure.
  • Patients will be asked to change into a gown, but may leave undergarments on.
  • Patients do not need to fast before this study.
  • Hygiene: Bathing is recommended to make sure that there are no oils, lotions, creams, or perfume on the skin. Please do not apply any of these items before the test. This will ensure the best results during the test.
  • Results are available to the ordering physician in three business days.

References

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