ISSN 2398-2942      

Electromyography

icanis
Contributor(s):

Simon Platt

Luc Poncelet


Introduction

  • Electromyography (EMG) covers methods that allow objective investigation of peripheral nerve, neuromuscular junction and muscle functioning. Useful complement to neurologic examination in hypotonic paresis and paralysis and in muscle weakness.
  • "Peripheral nerve" in its physiological sense includes nerve cell bodies in the brain stem, spinal cord and ganglions and nerve roots from which the peripheral nerve originates.
  • Electromyographic examination is divided into several procedures. The most reliable and widely used in a clinical setting are:
    • Detection electromyography.
    • Maximum motor nerve conduction velocity measurement.
    • Maximum sensory/mixed nerve conduction velocity measurement.
    • Repetitive motor nerve stimulation.
    • In addition, ventral roots can be specifically investigated through F-wave studies.
  • In detection EMG, muscles are investigated, looking for spontaneous electrical activity.
  • In motor nerve conduction velocity studies, repetitive stimulations and F-wave studies, motor nerves are electrically stimulated and resulting electrical activity in their target muscles, evaluated.
  • In sensory nerve conduction studies, nerves are stimulated and recordings obtained from the same nerves.
  • Denervated muscle fibers undergo many biochemical and physiological changes including:
    • Increase in sensitivity to acetylcholine.
    • Drifts in membrane potential.
  • These result in spontaneous potentials observed between 5 - 10 days after a nerve injury.
  • Parts of muscle fibers isolated from the end plate by a muscle lesion can survive and behave like denervated muscle cells, exhibiting spontaneous electrical activity.
  • In both cases, spontaneous activities can be recorded by detection EMG.
  • Disease processes may affect nerve cell body or processes, myelin sheaths or both. As a general rule, the larger a nerve fiber, the faster its conduction velocity. A larger fiber also has higher metabolic requirements and usually is more susceptible to insults. Disappearance of largest fibers results in a slight maximum conduction velocity drop and a marked diminution of the amplitude of the resulting muscle potential.
  • Myelin sheath damage induces dramatic conduction slowing and conduction blockade, both identifiable through nerve conduction studies.

Uses

  • Diagnostic technique to investigate neuromuscular abnormalities if neurological examination is inconclusive.
    • Gives picture of severity of lesion.
    • May localize it more or less precisely.
    • May discriminate whether nerve fibers or myelin sheaths in a nerve are most affected.

Advantages

  • Highly sensitive.
  • May evidence changes before they become clinically detectable.

Disadvantages

  • Material expensive.
  • Operator must be experienced
  • Method restricted to academic and referral institutions due to above.
  • Technical problems:
    • High quality grounding of the recording apparatus due to high amplifier gains.
    • Requires careful upkeep of electrodes and connecting wires.
    • Requires skillful operation.

Requirements

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Preparation

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Procedure

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Further Reading

Publications

Refereed papers

Motor nerve conduction velocity:

  • Recent references from PubMed and VetMedResource.
  • van Nes J J (1986) An introduction to clinical neuromuscular electrophysiology. Vet Quart (3), 233-239 PubMed.
  • van Nes J J (1986) Clinical application of neuromuscular electrophysiology in the dog: a review. Vet Quart (3), 240-250 PubMed.
  • Farnbach G C (1980) Clinical electrophysiology in veterinary neurology. Part I: Electromyography Comp Contin Edu Pract Vet 11, 791-797 ResearchGate.
  • Sims M H & Redding R W (1980) Maturation of nerve conduction velocity and the evoked muscle potential in the dog. Am J Vet Res 41 (8), 1247-1252 PubMed.
  • Brown N O & Zaki F A (1979) Electrodiagnostic testing for evaluation of neuromuscular disorders in dogs and cats. J Am Vet Med Assoc 174 (1), 86-90 PubMed.
  • Swallow J S & Griffiths I R (1977) Age related changes in the motor conduction velocity in dogs. Res Vet Sci 23 (1), 29-32 PubMed.
  • Lee A F & Bowen J M (1975) Effect of tissue temperature on ulnar nerve conduction velocity in the dog. Am J Vet Res 36 (9), 1305-1307 PubMed.
  • Lee A F & Bowen J M (1970) Evaluation of motor nerve conduction velocity in the dog. Am J Vet Res 31 (8), 1361-1366 PubMed.

Repetitive stimulation

  • Recent references from PubMed and VetMedResource.
  • Gödde T, Jaggy A, Vandevelde M et al (1993) Evaluation of repetitive nerve stimulation in young dogs. J Small Anim Pract 34 (8), 393-398 VetMedResource.
  • Malik R, Ho S & Church D B (1989) The normal response to motor nerve stimulation in dogsJ Small Anim Pract 30 (1), 20-26 VetMedResource.

Sensory/mixed nerve conduction velocity

  • Recent references from PubMed and VetMedResource.
  • van Nes J J (1985) Sensory action potentials in the ulnar and radial nerves of the dogs: effect of stimulation site and voltage. Am J Vet Res 46 (5), 1155-1161 PubMed.
  • Redding R W, Ingram J T & Colter S B (1982) Sensory nerve conduction velocity of cutaneous afferents of the radial, ulnar, peroneal, and tibial nerves of the dog: reference values. Am J Vet Res 43 (3), 517-21 PubMed.
  • Holliday TA, Ealand B G & Weldon B S (1977) Sensory nerve conduction velocity: technical requirements and normal values for branches of the radial and ulnar nerves of the dog. Am J Vet Res 38 (10), 1543-1551 PubMed.

F-waves and H-reflexes

  • Recent references from PubMed and VetMedResource.
  • Cuddon P A (1998) Electrophysiologic assessment of acute polyradiculoneuropathy in dogs: comparison with Guillain-Barre syndrome in people. J Vet Intern Med 12 (4), 294-303 PubMed.
  • Poncelet L & Balligand M (1991) Nature of the late potentials and F-ratio values in dogs. Res Vet Sci 51 (1), 1-5 PubMed.
  • Malik R & Ho S (1991) A new method for recording H-reflexes from the plantar muscles of dogs. J Small Anim Pract 32 (11), 547-556 VetMedResource.
  • Steiss J E (1984) Linear regression to determine the relationship between F-wave latency and limb length in control dogs. Am J Vet Res 45 (12), 2649-2650 PubMed.

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