EMG/Nerve Conduction Studies

 

 

o        EMG in Myopathy

         Usually no spontaneous activity is seen

         Diffuse loss of muscle fibers results in motor unites with fewer fibers, thus while the number of units is normal, the electrical activity of the unit is smaller than normal

         The number of motor unites recruited during contraction is normal, but the motor unites may be smaller than normal with normal or shorter than normal duration

o        EMG in Neuropathy

         Denervated muscle is hyperexcitable, resulting in spontaneous action potentials (fibrillations)

         With axonal loss, the number of motor units is reduced

         The remaining axons re-innervate some of the muscle fibers so that the remaining motor units are larger than normal and longer in duration

         The number of motor unites recruited during contraction is reduced with the units that are recruited larger than normal, longer in duration, and polyphasic in appearance

         Active Fasciculations

o        NCV in Myopathy