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Introduction ⬇

Electromyography (EMG) is a diagnostic procedure performed to evaluate muscle and nerve activity in response to stimulation. A nerve conduction velocity (NCV) test, also known as a nerve conduction study, is a test that measures how fast an electrical impulse travels through the nerve being evaluated. An NCV test is often performed along with an EMG. Electroneurography measures the speed of conduction of impulses along a peripheral nerve. Electromyoneurography (EMNG) combines EMG and electroneurography. These studies, performed to detect neuromuscular abnormalities, measure nerve conduction and electrical properties of skeletal muscles. Together with evaluation of range of motion, motor power, sensory defects, and reflexes, these tests can differentiate between neuropathy and myopathy. An EMG can define the site and cause of muscle disorders such as myasthenia gravis, muscular dystrophy, and myotonia; inflammatory muscle disorders such as polymyositis; and lesions that involve the motor neurons in the anterior horn of the spinal cord. EMG can also localize the site of peripheral nerve disorders such as radiculopathy and axonopathy. Skin and needle electrodes measure and record electrical activity. Electrical sound equivalents are amplified and recorded for later studies.

Procedure ⬆ ⬇

  1. The test is done in a copper-lined room to screen out outside interference.

  2. The patient may lie down or sit during the test.

  3. Apply a surface disk or lead strap to the skin around the wrist or ankle to ground the patient. Choose the muscles and nerves examined according to the patient's signs and symptoms, history, and physical condition (select nerves innervate specific muscles).

  4. Encourage the patient to relax (massage certain muscles to get the patient to relax) or to contract certain muscles (e.g., to point to toes) at specific times during the test.

  5. Testing is divided into two parts.

    The first test determines nerve conduction:

    1. Coat metal surface electrodes with electrode paste and firmly place over a specific nerve area. Pass electrical current (maximum, 100 mA for 1 msec) through the area to cause sensations, similar to shock from carpeting or static electricity or the equivalent of an AA battery, that are directly proportional to the time the current is applied. Patients with mild forms of neuromuscular disorders may feel mild discomfort, whereas those with polyneuropathies may experience moderate discomfort.

    2. Read the amplitude wave on an oscilloscope and record on magnetic tape for later studies.

    3. Electrical current leaves no mark but can cause unusual sensations that are not usually considered unpleasant. How fast and how well a nerve transmits messages can be measured. Nerves in the face, arms, or legs are appropriate for testing in this way.

    The second test determines muscle potential:

    1. Insert a monopolar electrode (a 1.25- to 7.5-cm-long, small-gauge needle) and incrementally advance into the muscle. Manipulate the needle without actually removing it to see if readings change, or place the needle in another muscle area.

    2. The electrode usually causes no pain unless the tip is near a terminal nerve. Ten or more needle insertions may be necessary. The needle electrode detects electricity normally present in muscle.

    3. Observe the oscilloscope for normal waveforms and listen for normal quiet sounds at rest. A "machine gun popping" sound or a rattling sound like hail on a tin roof is normally heard when the patient contracts the muscle.

    4. If the patient reports pain, remove the needle because the pain stimulus yields false results.

    5. Total examining time is 45-60 minutes if testing is confined to a single extremity; testing may take up to 3 hours for more than one extremity. There is no completely "routine" EMG. The length of the test depends on the clinical problem.

  6. Follow guidelines in Chapter 1 for safe, effective, informed intratest care.

Procedural Alert

  1. Enzyme levels that reflect muscle activity (e.g., aspartate aminotransferase, lactate dehydrogenase, creatine phosphokinase) must be determined before actual testing because the EMG causes elevation of these enzymes for up to 10 days postprocedure.

  2. Although rare, hematomas may form at needle insertion sites. Take measures, such as application of pressure to the site, to control bleeding. Notify the healthcare provider. Ascertain whether the patient is taking anticoagulants or aspirin-like drugs.

Clinical Implications ⬆ ⬇

  1. Abnormal neuromuscular activity occurs in diseases or disturbances of striated muscle fibers or membranes in the following conditions:

    1. Muscle fiber disorders (e.g., muscular dystrophy)

    2. Cell membrane hyperirritability; myotonia and myotonic disorders (e.g., polymyositis, hypocalcemia, thyrotoxicosis, tetanus, rabies)

    3. Myasthenia (muscle weakness states) caused by the following conditions:

      1. Myasthenia gravis

      2. Cancer due to nonpituitary adrenocorticotropic hormone secretion by the tumor:

        1. Bronchial cancer

        2. Sarcoid

      3. Deficiencies:

        1. Familial hypokalemia

        2. McArdle disease (muscle phosphorylase deficiency)

      4. Hyperadrenocorticism

      5. Acetylcholine-blocking agents:

        1. Curare

        2. Botulin

        3. Kanamycin

        4. Snake venom

  2. Disorders or diseases of lower motor neurons:

    1. Lesions involving motor neuron on anterior horn of spinal cord (myelopathy):

      1. Tumor

      2. Trauma

      3. Syringomyelia

      4. Juvenile muscular dystrophy

      5. Congenital amyotonia

      6. Anterior poliomyelitis

      7. Amyotrophic lateral sclerosis

      8. Peroneal muscular atrophy

    2. Lesions involving the nerve root (radiculopathy):

      1. Guillain-Barré syndrome

      2. Entrapment of the nerve root:

        1. Tumor

        2. Trauma

        3. Herniated disk

        4. Hypertrophic spurs

        5. Spinal stenosis

    3. Damage to or disease of peripheral or axial nerves:

      1. Entrapment of the nerve:

        1. Carpal or tarsal tunnel syndrome

        2. Facial, ulnar, radial, or peroneal palsy

        3. Meralgia paresthetica

      2. Endocrine:

        1. Hypothyroidism

        2. Diabetes

      3. Toxic:

        1. Heavy metals

        2. Solvents

        3. Antiamebicides

        4. Chemotherapy

        5. Antibiotics

    4. Early peripheral nerve degeneration and regeneration

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure. There is a risk for hematoma if the patient is on anticoagulant therapy.

  2. Administer sedation or analgesia as ordered.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Provide pain relief through appropriate interventions, as ordered.

  2. Promote rest and relaxation.

  3. Review test results; report and record findings. Modify the nursing care plan as needed.

  4. Monitor the patient for nerve and muscle disease. Provide assistance as necessary.

  5. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

  1. Conduction can vary with age and normally decreases with increasing age.

  2. Pain can yield false results.

  3. Electrical activity from extraneous persons and objects can produce false results as a result of movement.

  4. The test is ineffective in the presence of edema, hemorrhage, or thick subcutaneous fat.

Reference Values ⬆

Normal