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EMG Findings 01

Topic: Physiology

Created on Saturday, June 6 2009 by jdmiles

Last modified on Saturday, June 6 2009.


In the needle EMG study shown in the video above, the finding of motor unit action potentials that are large, long, and polyphasic would be most consistent with which of the following?

 
        A) A chronic lesion of the lower trunk of the brachial plexus
 
        B) An acute radial mononeuropathy
 
        C) A chronic sural mononeuropathy
 
        D) A chronic ulnar mononeuropathy
 
        E) A chronic radial mononeuropathy
 

 


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This question was created on June 06, 2009 by jdmiles.
This question was last modified on June 06, 2009.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ANSWERS AND EXPLANATIONS




A) A chronic lesion of the lower trunk of the brachial plexus

This answer is correct.


The EMG needle study above is examining the abductor pollicis brevis (APB) muscle. This muscle is innervated by the C8 and T1 nerve roots, the lower trunk, the medial cord, and the median nerve. Large, long, and polyphasic motor unit action potentials seen on EMG would provide evidence for a chronic neuropathic process involving one of these structures. Note that, with only this one needle study, it is impossible to determine which of these structures is affected. Also, with only this one needle study, a more diffuse process (such as a peripheral polyneuropathy) cannot be excluded.  (See References)

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B) An acute radial mononeuropathy

This answer is incorrect.


The EMG needle study above is examining the abductor pollicis brevis (APB) muscle. This muscle is innervated by the C8 and T1 nerve roots, the lower trunk, the medial cord, and the median nerve. Large, long, and polyphasic motor unit action potentials seen on EMG would provide evidence for a chronic neuropathic process involving one of these structures. Note that, with only this one needle study, it is impossible to determine which of these structures is affected. Also, with only this one needle study, a more diffuse process (such as a peripheral polyneuropathy) cannot be excluded.  (See References)

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C) A chronic sural mononeuropathy

This answer is incorrect.


The EMG needle study above is examining the abductor pollicis brevis (APB) muscle. This muscle is innervated by the C8 and T1 nerve roots, the lower trunk, the medial cord, and the median nerve. Large, long, and polyphasic motor unit action potentials seen on EMG would provide evidence for a chronic neuropathic process involving one of these structures. The sural nerve is a sensory nerve in the lower extremity.  (See References)

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D) A chronic ulnar mononeuropathy

This answer is incorrect.


The EMG needle study above is examining the abductor pollicis brevis (APB) muscle. This muscle is innervated by the C8 and T1 nerve roots, the lower trunk, the medial cord, and the median nerve. Large, long, and polyphasic motor unit action potentials seen on EMG would provide evidence for a chronic neuropathic process involving one of these structures. Note that, with only this one needle study, it is impossible to determine which of these structures is affected. Also, with only this one needle study, a more diffuse process (such as a peripheral polyneuropathy) cannot be excluded.  (See References)

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E) A chronic radial mononeuropathy

This answer is incorrect.


The EMG needle study above is examining the abductor pollicis brevis (APB) muscle. This muscle is innervated by the C8 and T1 nerve roots, the lower trunk, the medial cord, and the median nerve. Large, long, and polyphasic motor unit action potentials seen on EMG would provide evidence for a chronic neuropathic process involving one of these structures. Note that, with only this one needle study, it is impossible to determine which of these structures is affected. Also, with only this one needle study, a more diffuse process (such as a peripheral polyneuropathy) cannot be excluded.  (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. (ISBN:075067492X)Advertising:
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physiology
EMG Findings 01
Question ID: 060609115
Question written by J. Douglas Miles, (C) 2006-2009, all rights reserved.
Created: 06/06/2009
Modified: 06/06/2009
Estimated Permutations: 126000

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