Felis ISSN 2398-2950

Electromyography

Synonym(s): EMG

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 (or needle) 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 amplifier gains require high quality grounding of the recording apparatus.
    • 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

  • Pillai S R, Steiss J E & Wright J C (1991) Age-related changes in peripheral nerve conduction velocities of cats. Progress Vet Neurol (2), 95-104 VetMedResource.
  • Malik R & Ho S (1989) Motor nerve conduction parameters in the cat. JSAP 30 (7), 396-400 VetMedResource.
  • van Nes J J (1986) An introduction to clinical neuromuscular electrophysiology. Vet Quart (3), 233-9 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.
  • 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.

Repetitive stimulation

  • 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.

Sensory/mixed nerve conduction velocity

  • 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 (1984) Sensory nerve conduction velocity of cutaneous afferents of the radial, ulnar, peroneal, and tibial nerves of the cat: reference values. Am J Vet Res 45 (5), 1042-1045 PubMed.

F-waves and H-reflexes

  • Cuddon P A (1998) Electrophysiologic assessment of acute polyradiculoneuropathy in dogs: comparison with Guillain-Barré​ 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.
  • Knecht C D, Redding R W & Wilson S (1985) Characteristics of F and H waves of ulnar and tibial nerves in cats: reference values. Am J Vet Res 46 (4), 977-979 PubMed.
  • Gassel M M & Wiesendanger M (1965) Recurrent and reflex discharges in plantar muscles of the cat. Acta Physiol Scand 65 (1-2), 138-142 Wiley Online Library.


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