Advertisement

Electrophysiology of Myopathy

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

Abstract

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 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Suggested Reading

  1. Aminoff MJ. Electromyography in Clinical Practice, 3rd ed. Churchill Livingstone, New York, NY, 1998.Google Scholar
  2. Ball RD. Basics of needle electromyography. An AAEE Workshop. AAEM, 1985, Rochester, MN.Google Scholar
  3. Bromberg MD, Albers JW. Electromyography in idiopathic myositis. Mt Sinai J Med 1988;55(6): 459–464.PubMedGoogle Scholar
  4. Daube JR. AAEM minimonograph #11: needle examination in electromyography. Muscle Nerve 1991;14: 685–700.PubMedCrossRefGoogle Scholar
  5. Daube JR. Electrodiagnosis of muscle disorders. In: Myology (Engel AG, Franzini-Armstrong C, eds.). McGraw-Hill, New York, NY, 1994.Google Scholar
  6. DeGirolami U, Smith TW. Pathology of skeletal muscle. Am J Pathol 1982; 107: 235–276.Google Scholar
  7. Dumitru D. Myopathies. In: Electrodiagnostic Medicine (Dumitru D, ed). Hanley and Belfus, Philadelphia, PA 1994.Google Scholar
  8. Ferrante MA, Wilbourn AJ. In: Comprehensive Clinical Neurophysiology (Levin K, Luders H, eds.). WB Saunders, Philadelphia, PA, 2000, pp. 268–280.Google Scholar
  9. Kandel ER, Schwartz JH, Jessell TM. Essentials of Neural Science and Behavior. Appleton and Lange, Stamford, CT, 1995, pp. 212.Google Scholar
  10. Katirji B. Electromyography in Clinical Practice. St. Louis, Mosby, 1998.Google Scholar
  11. Kimura J. Electrodiagnosis in Diseases of Nerve and Muscle: Principles and Practice. Oxford University Press, New York, NY, 2001. WB Saunders, Philadelphia, 19.Google Scholar
  12. Oh SJ. Principles of Electromyography. Williams and Wilkins, Baltimore, MD, 1998.Google Scholar
  13. Phillips LH, Litchy WJ, Auger RG, et al. AAEM Glossary of terms in electrodiagnostic medicine. Muscle Nerve 2001; Suppl 10.Google Scholar
  14. Preston DC, Shapiro BE. Electromyography and Neuromuscular Disorders. Clinical-Electrophysiological Correlations. Butterworth-Heinemann, Boston, MA, 1998.Google Scholar
  15. Westmoreland BE, Benarroch EE, Daube JR, Reagan TJ, Sandok BA. Medical Neurosciences. An Approach to Anatomy, Pathology and Physiology by Systems and Levels. Little Brown and Co., Boston, MA, 1994, pp. 353.Google Scholar
  16. Wilbourn AJ. The electrodiagnostic examination with myopathies. J Clin Neurophysiol 1993; 10: 132–148.PubMedCrossRefGoogle Scholar

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

Personalised recommendations