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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) Positive sharp waves
 
        B) Complex repetitive discharges
 
        C) Neuromyotonia
 
        D) Cramps
 
        E) Endplate spikes
 

 


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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) 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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B) complex repetitive discharges

This answer is incorrect.


Complex repetitive discharges (CRDs) represent the firing of many muscle fibers, in a sequential, time-locked pattern. CRDs can fire at 5 - 100 Hz. The firing pattern is perfectly regular, giving CRDs a machine-like quality on speaker. CRDs have a stable amplitude, but the number of muscle fibers involved may change abruptly. This can result in a sudden change in firing pattern and amplitude.  (See References)

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C) neuromyotonia

This answer is incorrect.


Neuromyotonia represents the very rapid spontaneous firing of a motor unit. Amplitude and frequency both start high, and then wane with time. Firing frequencies range from 150 - 250 Hz.  (See References)

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D) cramps

This answer is incorrect.


Cramps represent the rapid firing of a motor unit or many motor units. The amplitude is typically stable. Frequencies range from 20 to 150 Hz.  (See References)

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E) endplate spikes

This answer is incorrect.


Endplate spikes result from the firing of muscle fibers. They have a brief spike, diphasic morphology, with an initial negative deflection. They have a stable amplitude, a firing rate of 5 - 50 Hz, and an irregular, sputtering 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

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