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Nerve Injuries Affecting the Upper Extremity

Topic: Pharmacology

Created on Thursday, December 21 2006 by jdmiles

Last modified on Thursday, December 21 2006.

A Greek female deity was gouged in the axilla by a Narwhal yesterday. She presents to your clinic today complaining of numbness in the area shaded in green in the image above. She also, as pictured, is unable to extend her arm at the elbow. Abduction at the shoulder has been spared. Of the following options, which is the most likely site of the lesion?

 
        A) Radial nerve
 
        B) Anterior interosseous nerve
 
        C) Posterior interosseous nerve
 
        D) Right cranial nerve VI
 
        E) Spinal accessory nerve
 

 


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This question was created on December 21, 2006 by jdmiles.
This question was last modified on December 21, 2006.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ANSWERS AND EXPLANATIONS




A) radial nerve

This answer is correct.


The sensory distribution shown, with weakness of the triceps (inability to extend the arm at the elbow) could be consistent with a posterior cord lesion, or a radial nerve lesion. Abduction of the shoulder is intact, however, suggesting that the innervation of the deltoid is not affected. The deltoid is innervated by the axillary nerve, which comes off the posterior cord. Therefore, this is most likely a radial nerve lesion.   (See References)

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B) anterior interosseous nerve

This answer is incorrect.


A lesion of the anterior interosseous nerve would not result in weak extension at the elbow, but would impair flexion of the thumb and forefinger. A lesion of this nerve would not cause numbness.   (See References)

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C) posterior interosseous nerve

This answer is incorrect.


The posterior interosseous nerve is a distal motor branch of the radial nerve. It branches off the radial nerve distal to the elbow, and does not affect arm extension. It does affect finger flexion. A lesion of this nerve would not cause numbness.   (See References)

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D) right cranial nerve VI

This answer is incorrect.


A lesion affecting the abducens nerve (CN VI) would result in impaired abduction of the eye ipsilateral to the lesion. This answer is just plain silly.   (See References)

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E) spinal accessory nerve

This answer is incorrect.


A lesion of the spinal accessory nerve would result in weakness of the trapezius and sternocleidomastoid. It would not result in sensory loss of the upper extremity, nor in impaired extension at the elbow.   (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. Pp. 663-666.
2. Leigh, R.J., and Zee, D.S. (2006). The Neurology of Eye Movements, 4th Edition. Oxford University Press, Oxford.
3. Bickley, L.S., and Hoekelman, R.A. (1999). Bates' Guide to Physical Examination and History taking, 7th Edition. Lippincott, Philadelphia. Pp. 163-244.
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pharmacology
Nerve Injuries Affecting the Upper Extremity
Question ID: 12210600
Question written by J. Douglas Miles, (C) 2006-2009, all rights reserved.
Created: 12/21/2006
Modified: 12/21/2006
Estimated Permutations: 201600

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