- See:
- Nerve Injury:
- Nerve Menu
- outside links:
- The Expert Electromyographer
- EMG Table of Contents
- EMG Findings in Specific Conditions:
- Normal Study:
- normal insertional activity;
- silent rest activity;
- biphasic and triphasic potentials;
- complete interference;
- Neuropraxia
- normal insertional activity;
- silent rest activity;
- no biphasic and triphasic potentials;
- interference: none
- Axonotmesis:
- increased insertional activity;
- rest activity: fibrillations & positive sharp waves;
- no biphasic and triphasic potentials;
- interference: none
- Neurotmesis
- increased insertional activity;
- rest activity: fibrillations & positive sharp waves;
- no biphasic and triphasic potentials;
- interference: none
- Axonal Neuropathies:
- increased insertional activity;
- rest activity: fibrillations & positive sharp waves;
- no biphasic and triphasic potentials;
- interference: incomplete;
- Demyelinating Neuropathies
- normal insertional activity;
- silent rest activity;
- no biphasic and triphasic potentials;
- interference: incomplete;
- Anterior Horn Disease
- increased insertional activity;
- rest activity: fibrillations & positive sharp waves;
- large polyphasic contractions;
- Myopathic Disorders
- Neuropathic Disorders
- 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:
- 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;
- Nerve Entrapment:
- Motor Conduction Latency:
- 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.