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Spontaneous Activity on Needle EMG 01

Topic: Physiology

Created on Thursday, January 18 2007 by jdmiles

Last modified on Thursday, January 18 2007.

You are performing a needle EMG study. You notice spontaneous discharges. They are single discharges, stable in amplitude, firing at a rate of about 10 Hz with a regular rhythm. Of the following choices, what are these discharges most likely to be?

A) Myokymia

B) Myotonia

C) Endplate noise

D) Multiplets

E) Positive sharp waves

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This question was created on January 18, 2007 by jdmiles.
This question was last modified on January 18, 2007.

ANSWERS AND EXPLANATIONS

A) myokymia

This answer is incorrect.

Myokymia is the periodic rapid burst firing of a motor unit. The amplitude is usually stable, although the number of discharges in each burst may vary. Each burst represents a single motor unit firing at 5 - 60 Hz. Bursts occur 1 to 5 times per second. (See References)


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B) myotonia

This answer is incorrect.

Myotonia results from the rapid firing of muscle fibers. The discharges have brief spike or positive wave morphology. The amplitude of the discharges waxes and wanes, as does the frequency, which can range from 20-150 Hz. (See References)


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C) endplate noise

This answer is incorrect.

Endplate noise is generated by the random activity of miniature endplate potentials. The individual discharges are monophasic and negative in morphology. These discharges fire at 20-40 Hz, with an irregular pattern, giving endplate noise a hissing quality on speaker. Endplate noise is detected only when the needle is in close proximity to the motor endplate. (See References)


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D) multiplets

This answer is incorrect.

Multiplets represent 2, 3 or more motor units firing together in bursts. The amplitde of the discharges is usually stable. Frequency is typically 1-50 Hz. (See References)


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E) positive sharp waves

This answer is correct.

Positive sharp waves result from the firing of muscle fibers. They have a diphasic morphology, with an initial positive deflection followed by a slow negative phase. They have a stable amplitude, a firing rate of 0.5 - 10 Hz, and a regular firing pattern. (See References)


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References:

1. Preston, D.C., and Shapiro, B.E. (2005). Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic Correlations, 2nd Edition. Elsevier, Philadelphia.


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physiology
Spontaneous Activity on Needle EMG 01
Question ID: 0118200700
Question written by J. Douglas Miles, (C) 2006-2009, all rights reserved.
Created: 01/18/2007
Modified: 01/18/2007
Estimated Permutations: 50400