FrontalCortex, Inc. is a non-profit corporation dedicated to neurology education.

Lower Extremity EMG 01

Topic: Anatomy

Created on Tuesday, February 13 2007 by jdmiles

Last modified on Tuesday, February 13 2007.

A patient presents with lower extremity weakness. Needle EMG study of the gastrocnemius and gluteus maximus reveals large, long, polyphasic motor unit action potentials. Needle EMG study of the vastus medialis, vastus lateralis, extensor digitorum longus and tibialis anterior are normal. Motor and sensory NCS are normal. Of the following options, which is the most likely lesion?

A) Acute S1 radiculopathy

B) Acute L4 radiculopathy

C) Acute L5 radiculopathy

D) Chronic S2 radiculopathy

E) Chronic L5 radiculopathy

	= Go back to the top of the page.
	= Reload a different version of this question ().
	= Load a random question from the database.
	= Use this question as a template to create a totally NEW question.
	= Enter detailed rating for this question!
	= How users like you have rated this question.

This question was created on February 13, 2007 by jdmiles.
This question was last modified on February 13, 2007.

ANSWERS AND EXPLANATIONS

A) acute S1 radiculopathy

This answer is incorrect.

Given the pattern of muscles involved, this could be an S1 lesion. However, the abnormal MUAPs found were long, large, and polyphasic, suggesting a chronic denervation. There is no other evidence to suggest an acute denervation. (See References)


Please log in if you want to rate questions.

B) acute L4 radiculopathy

This answer is incorrect.

The abnormal MUAPs found were long, large, and polyphasic, suggesting a chronic denervation. There is no other evidence to suggest an acute denervation. The abnormal MUAPs were found only in gastrocnemius (S1, S2), and gluteus maximus (L5, S1, S2), neither of which has innervation from L4. The muscles innervated by L4 - vastus medialis (L2, L3, L4), vastus lateralis (L2, L3, L4), extensor digitorum longus (L4, L5), and tibialis anterior (L4, L5) - had normal needle studies. Thus, L4 is not the location of the lesion. (See References)


Please log in if you want to rate questions.

C) acute L5 radiculopathy

This answer is incorrect.

The abnormal MUAPs found were long, large, and polyphasic, suggesting a chronic denervation. There is no other evidence to suggest an acute denervation. Abnormal MUAPs were found in gluteus maximus (L5, S1, S2), but not in other muscles innervated by L5 - extensor digitorum longus (L4, L5) and tibialis anterior (L4, L5). Also, abnormal MUAPs were found in gastrocnemius (S1, S2), which does not receive innervation from L5. S1 or S2 would be more likely locations for the lesion than L5. (See References)


Please log in if you want to rate questions.

D) chronic S2 radiculopathy

This answer is correct.

The abnormal MUAPs found were long, large, and polyphasic, suggesting a chronic denervation. The muscles involved all had S1 innervation: gastrocnemius (S1, S2), and gluteus maximus (L5, S1, S2). The other muscles are normal, suggesting no chronic denervation: vastus medialis (L2, L3, L4), vastus lateralis (L2, L3, L4), extensor digitorum longus (L4, L5), and tibialis anterior (L4, L5). This makes S2 a more likely location than the other options. Note that S1 could also be involved. (See References)


Please log in if you want to rate questions.

E) chronic L5 radiculopathy

This answer is incorrect.

Abnormal MUAPs were found in gluteus maximus (L5, S1, S2), but not in other muscles innervated by L5 - extensor digitorum longus (L4, L5) and tibialis anterior (L4, L5). Also, abnormal MUAPs were found in gastrocnemius (S1, S2), which does not receive innervation from L5. S1 or S2 would be more likely locations for the lesion than L5. (See References)


Please log in if you want to rate questions.

References:

1. Preston, D.C., and Shapiro, B.E. (2005). Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic Correlations, 2nd Edition. Elsevier, Philadelphia.
2. Guarantors of Brain. (2000). Aids to the Examination of the Peripheral Nervous System, fourth edition. W.B. Saunders, Edinburgh.
3. Moore, K.L. (1992). Clinical Oriented Anatomy, 3rd Edition. Williams & Wilkins, Baltimore.


Please log in if you want to rate questions.

FrontalCortex.com -- Neurology Review Questions -- Neurology Boards -- Board Review -- Residency Inservice Training Exam -- RITE Exam Review
anatomy
Lower Extremity EMG 01
Question ID: 021307133
Question written by J. Douglas Miles, (C) 2006-2009, all rights reserved.
Created: 02/13/2007
Modified: 02/13/2007
Estimated Permutations: 50400