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Electromyography and Motor Nerve Conduction Velocity 1097.e1

Electromyography and Motor Nerve Conduction Velocity Client Education
Sheet
VetBooks.ir
Preparation: Important
Difficulty level: ♦♦♦
Checkpoints Procedure
The animal is premedicated, anesthetized,
Synonyms • Monitor body temperature and prevent hypo- intubated, and maintained with oxygen and an
Electrodiagnostics, EMG, NCV thermia, which prolongs nerve conduction inhalation anesthetic and in lateral recumbency
times (1.8 m/sec drop for every 1°C drop for the EMG procedure.
Overview and Goals in limb temperature). • Needle electrodes are used for recording
• Integral component of diagnostic evaluation • Draw blood for serum biochemistry profile electrical activity in major muscle groups
of animals suspected of having neuromus- before procedure because EMG will cause a in appendicular muscles and in epaxial and
cular disorders (neuropathy, myopathy, transient increase in creatine kinase. masticatory muscles; rarely, esophageal and
neuromuscular junctional disease) laryngeal muscles and tongue.
• May confirm and characterize the presence Possible Complications and • Evaluation is performed by listening for Procedures and Techniques
of nerve, neuromuscular junction, or muscle Common Errors to Avoid characteristic sounds of electrical potentials
disease in these animals • Complications related to anesthesia and by visually examining the waveforms
• Useful for differentiating denervation from • Regurgitation and aspiration pneumonia produced by the potentials on the monitor.
disuse atrophy in animals with megaesophagus/esophageal • Sensitivity is greatly increased by increasing
• Sensitivity is good (most neuromuscular dysfunction or dysphagia the number of passes through the muscle
diseases produce abnormal results), but speci-
ficity is poor (results are rarely characteristic
of a specific disease).
• Generally part of a diagnostic workup that
may also involve nerve and muscle biopsy,
cerebrospinal fluid (CSF) analysis, labora-
tory testing (serology, endocrine testing,
measurement of metabolites), radiographs,
and advanced imaging (MRI or CT)
Indications
• Animals with clinical signs and neurologic
examination suggestive of neuromuscular
disease (diffuse or focal) A
• Animals with peripheral nerve injuries
• May help confirm the presence of endocrine
disease (hyperadrenocorticism/pseudomyotonia)
Contraindications
Electrodiagnostics require general anesthesia,
and relative contraindications include mega-
esophagus or severe weakness (hypoventilation).
Equipment, Anesthesia
• General anesthesia and tracheal intubation
are required. For sensory nerve conduction
studies in which paralysis with atracurium B
is required, a ventilator is needed.
• Ideally should be performed in electrically
shielded room to minimize background noise
• Differential amplifier, computer with appro-
priate software for labeling and calculations,
needle electrodes for stimulating and recording
impulses (concentric needle electrode preferred
for electromyography [EMG]), isopropyl
alcohol, and measuring tape
• Surgical pack: often, muscle and nerve
biopsies are done after electrodiagnostics.
• If indicated for nutritional support, a percu-
taneous endoscopic gastrostomy (PEG) tube C
can be placed after the procedure, while the
animal is anesthetized. ELECTROMYOGRAPHY AND MOTOR NERVE CONDUCTION VELOCITY Types of electrical activity
seen in normal muscle during electromyography evaluation. A, Insertional activity. Note abrupt onset and
Anticipated Time termination of activity associated with needle placement (100 mV/div; 200 msec/div). B, Miniature endplate
• EMG: 10-20 minutes potentials with two endplate spikes indicating close proximity of needle to an endplate (100 mV/div; 10 msec/
div). C, Motor unit action potentials seen during voluntary muscle activity in an awake animal (100 mV/div;
• EMG + nerve conduction velocity (NCV): 10 msec/div). (Reprinted with permission from Cuddon PA: Electrophysiology in neuromuscular disease. Vet Clin
40-60 minutes North Am Small Anim Pract 32:31-62, 2002.)
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