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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) Endplate spikes
 
        B) Rest tremor
 
        C) Fibrillation potentials
 
        D) Cramps
 
        E) Fasciculations
 

 


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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) 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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B) rest tremor

This answer is incorrect.


In patients who have a rest tremor, (for example, a parkinsonian tremor) the tremor remains present and active during an EMG study, and the muscle activity caused by the tremor is detected on needle EMG. The firing motor units produce bursts of activity separated by inactivity. Bursts occur at 1 - 5 times per second. Each burst represents the synchronous firing of many different motor units. The amplitude of the discharges rises and falls.  (See References)

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C) fibrillation potentials

This answer is correct.


Fibrillation potentials result from the firing of muscle fibers. They have a brief spike, diphasic or triphasic morphology, and their initial deflection is positive. They have a stable amplitude, a firing rate of 0.5 - 10 Hz, and a regular firing pattern.  (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) fasciculations

This answer is incorrect.


Fasciculations represent firing of whole motor units. The discharges are stable in amplitude, with an irregular firing rhythm and a rate of 0.1 to 10 Hz.  (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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