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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) Rest tremor
 
        B) Myokymia
 
        C) Cramps
 
        D) Neuromyotonia
 
        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) 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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B) 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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C) 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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D) 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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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

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