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Nerve Injuries Affecting the Upper Extremity

Topic: Pharmacology

Created on Friday, December 22 2006 by jdmiles

Last modified on Friday, December 22 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.
Needle EMG is likely to show fibrillations in which of the following muscles?

 
        A) Flexor carpi radialis
 
        B) Deltoid
 
        C) Latissimus dorsi
 
        D) Extensor carpi ulnaris
 
        E) Fibrillations would not be expected on needle EMG given this history
 

 


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This question was created on December 22, 2006 by jdmiles.
This question was last modified on December 22, 2006.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ANSWERS AND EXPLANATIONS




A) flexor carpi radialis

This answer is incorrect.


The sensory and motor deficits this patient complains of are consistent with a radial nerve injury. Fibrillations will eventually be seen in the muscles innervated by the radial nerve: triceps, brachioradialis, extensor carpi radialis longus, supinator, extensor carpi ulnaris, extensor digitorum, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. No fibrillations will be seen on today's study. Furthermore, the flexor carpi radialis is not innervated by the radial nerve. It is innervated by the median nerve.   (See References)

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B) deltoid

This answer is incorrect.


The sensory and motor deficits this patient complains of are consistent with a radial nerve injury. Fibrillations will eventually be seen in the muscles innervated by the radial nerve: triceps, brachioradialis, extensor carpi radialis longus, supinator, extensor carpi ulnaris, extensor digitorum, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. No fibrillations will be seen on today's study. Furthermore, the deltoid is not innervated by the radial nerve. It receives innervation from the axillary nerve. Both axillary and radial nerve are branches of the posterior cord, but in this patient, the history specifically mentions that adduction of the shoulder is intact.   (See References)

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C) latissimus dorsi

This answer is incorrect.


The sensory and motor deficits this patient complains of are consistent with a radial nerve injury. Fibrillations will eventually be seen in the muscles innervated by the radial nerve: triceps, brachioradialis, extensor carpi radialis longus, supinator, extensor carpi ulnaris, extensor digitorum, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. No fibrillations will be seen on today's study. Furthermore, the latissimus dorsi is not innervated by the radial nerve. It receives innervation directly off the brachial plexus.   (See References)

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D) extensor carpi ulnaris

This answer is incorrect.


The sensory and motor deficits this patient complains of are consistent with a radial nerve injury. Fibrillations will eventually be seen in the muscles innervated by the radial nerve: triceps, brachioradialis, extensor carpi radialis longus, supinator, extensor carpi ulnaris, extensor digitorum, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. However, these will only start to be seen in the most proximal muscles at least 2 weeks after the injury. At this time, this injury should not result in fibrillations. Any fibrillations seen on needle EMG would have to be due to some other cause.   (See References)

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E) fibrillations would not be expected on needle EMG given this history

This answer is correct.


The sensory and motor deficits this patient complains of are consistent with a radial nerve injury. Fibrillations will eventually be seen in the muscles innervated by the radial nerve: triceps, brachioradialis, extensor carpi radialis longus, supinator, extensor carpi ulnaris, extensor digitorum, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. However, these will only start to be seen in the most proximal muscles at least 2 weeks after the injury. At this time, this injury should not result in fibrillations. Any fibrillations seen on needle EMG would have to be due to some other cause.   (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. 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: 12220602
Question written by J. Douglas Miles, (C) 2006-2009, all rights reserved.
Created: 12/22/2006
Modified: 12/22/2006
Estimated Permutations: 291657600

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