- 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