What is the role of electromyography (EMG) and nerve conduction studies (NCS) in the diagnosis of Guillain-Barre syndrome (GBS)?

Updated: Jul 14, 2021
  • Author: Michael T Andary, MD, MS; Chief Editor: Milton J Klein, DO, MBA  more...
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Electromyography (EMG) and nerve conduction studies (NCS) can be very helpful in the diagnosis. Abnormalities in NCS that are consistent with demyelination are sensitive and represent specific findings for classic GBS. Delayed distal latencies, slowed nerve conduction velocities, temporal dispersion of waveforms, conduction block, prolonged or absent F waves, and prolonged or absent H-reflexes are all findings that support demyelination. Needle EMG may be normal in acute nerve lesions, and it may take 3-4 weeks for fibrillation to develop. In the acute phase, the only needle EMG abnormality may be abnormal motor recruitment, with decreased recruitment and rapid firing motor units in weak muscles. Unfortunately, electrodiagnostic studies can be completely normal in acute GBS and a normal study does not rule GBS. [109, 110]

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