Electrophysiology of Myopathy

Approach to the Patient With Myopathy in the EMG Laboratory
  • Nithi S. Anand
  • David Chad


The myopathic disorders represent a heterogeneous group of diseases with a variety of causes. Although electrodiagnostic testing rarely allows an entirely specific diagnosis to be made, such testing can be extremely helpful in first confirming the presence of myopathy and therefore helping to appropriately categorize it. Standard motor nerve conduction studies generally do not demonstrate substantial abnormalities, except occasional reductions in compound motor potential amplitude in severe cases or where predominantly distal disease is present. Needle EMG remains the most important part of neurophysiological examination. In most myopathic conditions, spontaneous activity is increased, although it is most prominently increased in inflammatory or necrotizing myopathic processes. The presence of myotonic discharges can be very helpful in limiting the differential diagnosis. Complex repetitive discharges, which are present in myopathic conditions, are nonspecific. Motor unit potentials in myopathy are generally of low-amplitude and short duration, except in very chronic conditions, in which the motor unit potentials can actually become of long duration and high amplitude. Finally, it is critical to remember that an entirely normal EMG does not exclude the presence of myopathy.

Key Words

Dermatomyositis fibrillation potential myopathy myositis myotonic discharge myotonic dystrophy polymyositis 


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Copyright information

© Humana Press Inc. 2007

Authors and Affiliations

  • Nithi S. Anand
    • 1
  • David Chad
    • 1
  1. 1.Department of NeurologyUniversity of Massachusetts Medical CenterWorcester

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