EMG of Myopathic Disorders

- Discussion:
    - as general rule, an EMG of patient who has myopathic disease shows a decreased amplitude & duration of response, compared w/ that of unaffected pt,
          while an EMG of pt who has neuropathic disorder shows an increased amplitude and duration of response;
          - EMG studies are generally useful for excluding neurogenic disorders and confirming either active or inactive myopathy;
    - short duration (consisent finding), low-amplitude polyphasic units (which is variable) on voluntary activation;
    - appearance of small amplitudes (variable) & short duration (consistent) and polyphasic waves, are related to a loss of muscle fibers within the motor units;
          - there is rapid recruitment of motor units w/ complete interference pattern of reduced amplitude on weak effort;
    - increased spontaneous activity w/ fribrillations, complex repetitive discharges, and positive sharp waves;
          - fibrillations w/ positive sharp wave can be seen in inflammatory myopathies, muscular dystrophies, and some toxic mypathies;
          - this EMG pattern occurs in a variety of acute, toxic, and active myopathic processes and should not be considered diagnostic for the inflammatory myopathies;
   - mixed myopathic and neurogenic potentials (polyphasic units of short and long duration) may also be present as a consequence of the regeneration of muscle
          fibers and chronicity of the disease

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, May 31, 2012 10:52 am