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Nerve Injury:
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Nerve Menu
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outside links:
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The Expert Electromyographer
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EMG Table of Contents:
- EMG Findings in Specific Conditions:
- Normal Study:
- normal
insertional activity;
- silent
rest activity;
- biphasic and triphasic potentials;
- complete interference;
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Neuropraxia
- normal
insertional activity;
- silent
rest activity;
- no biphasic and triphasic potentials;
- interference: none
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Axonotmesis:
- increased
insertional activity;
-
rest activity:
fibrillations &
positive sharp waves;
- no biphasic and triphasic potentials;
- interference: none
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Neurotmesis
- increased
insertional activity;
-
rest activity:
fibrillations &
positive sharp waves;
- no biphasic and triphasic potentials;
- interference: none
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Axonal Neuropathies:
- increased
insertional activity;
-
rest activity:
fibrillations &
positive sharp waves;
- no biphasic and triphasic potentials;
- interference: incomplete;
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Demyelinating Neuropathies
- normal insertional activity;
- silent
rest activity;
- no biphasic and triphasic potentials;
- interference: incomplete;
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Anterior Horn Disease
- increased
insertional activity;
-
rest activity:
fibrillations &
positive sharp waves;
- large polyphasic contractions;
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Myopathic Disorders
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Neuropathic Disorders
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Peripheral Neuropathy
- Indications for EMG:
- EMG studies are highly sensitive, but results are nonspecific;
- to evaluate motor neuron dysfunction;
- confirme & extension of clinical examination;
- useful in localizing level of specific lesion, distinguishing between partial and complete lesions, differentiating primary muscle
or nerve pathology, & evaluating malingerers;
- useful for diff dx & in presence of coexisting disease;
- radiculopathy due to dz of C-spine, diffuse peripheral neuropathy, or proximal median neuropathy can pose clinical questions that electrodiagnostic testing can answer;
- no other test has a higher diagnostic accuracy in patients w/ final diagnosis of
carpal tunnel syndrome;
- Technique:
- small needle is inserted into muscle to record electrical activity of several neighboring motor units;
- Specific Measurements:
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Rest Activity:
- S wave:
- occurs when action potentials travel from the point of stimulation of peripheral nerve to the spinal cord and back to the muscle;
- another factor that may lead to normal EMG in presence of compressive radiculopathy is overlapping motor innervation of single muscle;
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Nerve Entrapment:
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Motor Conduction Latency:
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Sensory latency:
- F wave:
- F wave is often measured to supplement routine nerve conduction studies because the F wave permits evaluation of the proximal segments of peripheral nerves;
- F waves are valuable in evaluating disorders involving the nerve roots, plexuses and the proximal segments of peripheral nerves;
- determine of F wave latencies is particularly valuable in evaluating patients with demyelinating paolyradiculopathies;
- Number of motor units under voluntary control;
- Duration and Amplitude of each Motor Unit Potential;
Clinical and electromyographic study of seven spastic children with internal rotation gait.
Sutherland DH, Schottstaedt ER, Larsen LI, et al: J Bone Joint Surg 1969; 51A:1070-1082.
