AUTHOR INFORMATION

Section 1 of 9

Authored by Elizabeth A Sekul, MD, Associate Professor, Department of Neurology, Medical College of Georgia

Elizabeth A Sekul, MD, is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Child Neurology Society

Edited by Aashit K Shah, MD, Associate Professor of Neurology, Wayne State University; Program Director, Clinical Neurophysiology Fellowship, Department of Neurology, Detroit Medical Center; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Glenn Lopate, MD, Associate Professor, Department of Neurology, Division of Neuromuscular Diseases, Washington University School of Medicine; Chief of Neurology, St Louis ConnectCar; Consulting Staff, Barnes Jewish Hospital; Matthew J Baker, MD, Consulting Staff, Collier Neurologic Specialists, Naples Community Hospital; and Nicholas Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants

Author's Email:	Elizabeth A Sekul, MD
Editor's Email:	Aashit K Shah, MD

eMedicine Journal, August 9 2005, VOLUME 6, Number 8

INTRODUCTION

Section 2 of 9

Background: Mononeuropathies can occur secondary to direct trauma, compression, stretch injury, ischemia, infection, or inflammatory disease.

Nerve entrapments are due to compression of the nerve by either normal structures or an external source. The most common nerve entrapments are at the median nerve of the wrist (ie, carpal tunnel syndrome) and ulnar nerve of the elbow (ie, cubital tunnel syndrome).

In the lower extremity, peroneal neuropathy is the most common isolated mononeuropathy. In patients of our electrodiagnostic laboratory, it is the third most common mononeuropathy overall.

Pathophysiology: Compression and entrapment neuropathies are predominantly demyelinating.

• Myelin loss results in slowing of the nerve conduction through the area involved.

• When acute compression occurs, this may result in a conduction block. When the compression is more chronic, only slowing across the involved segment may be seen.

• When compression is severe, ischemic changes occur that cause secondary axonal damage.

• Pure demyelinating lesions typically have a better capacity to recover.

The pathophysiology of ischemic injuries and nerve transection is axonal damage. When axonal damage occurs, recovery is slower and longer and may not be complete.

• This results in wallerian degeneration distally, and recovery requires the nerve to regenerate and reinnervate.

• This process is slower than healing from other types of injuries and may not be complete.

• Nerve conduction studies and electromyography (EMG) can aid in defining the lesion location and type.

Knowledge of peroneal nerve anatomy is essential to understanding the mechanism of its injury and to localizing the site of the lesion.

• The peroneal nerve is a division of the sciatic nerve, which splits at or slightly above the popliteal fossa to form the tibial and common peroneal nerves.

• The common peroneal nerve extends anterolaterally to wind around the neck of the fibula.

• At this level, the nerve is superficial, covered only by skin and subcutaneous tissue. Here, it is predisposed to direct compression.

• The nerve then dives into the peroneus longus muscle, where tethering can occur, making it susceptible to stretch injury at this level.

• The nerve then divides into the superficial and deep peroneal branches.
  • The superficial branch supplies the foot everters and sensation to the skin of the lateral calf and dorsum of the foot.

  • The deep peroneal branch supplies the foot and toe dorsiflexors and has a small sensory component, which innervates only the skin of the web space between the first and second toes.

Race: No racial predilection is known.

Sex: No gender proclivity is known.

Age: This neuropathy is uncommon in children but has been reported in all age groups.

CLINICAL

Section 3 of 9

History:

• Patients present with frequent tripping due to a foot drop.



• Night cramps may occur in the anterior lower leg early in the course (if the compression is chronic).



• If the compression is acute, the symptoms are likely to be maximal at onset.



• Pain may occur at the site of compression.



• Sensory disturbances (eg, tingling, numbness) in the lateral lower leg and foot may be noted.

Physical:

• If the lesion is severe, a complete foot drop that spares plantar flexion and foot inversion is noted.



• The gait will be high-stepping with "foot slapping."



• In milder cases, weakness of foot eversion and dorsiflexion may be noted only by asking the patient to walk on his or her heels.



• Tapping of the nerve at the fibular head may produce pain and tingling in the peroneal sensory nerve distribution.



• Distribution of peroneal sensory disturbance assists in localizing the lesion. Numbness in the lower part of the lateral distal leg suggests superficial peroneal sensory involvement, while numbness of the upper part of the lateral distal leg suggests deep peroneal sensory distribution (see Picture 1). With common peroneal lesions, sensory loss is noted over the lateral calf and dorsum of the foot but spares the fifth toe.

Causes:

• Peroneal neuropathies classically are associated with external compression at the level of the fibular head.



• The most common etiology is habitual leg crossing (which compresses this area).



• Prolonged positioning with pressure at this area (eg, sitting on an airplane or positioning during surgery) are other causes.



• Short casts or braces around this area can be factors in external compression.



• Other causes include operative trauma (knee surgery), fibular fracture, blunt or open trauma, and intrinsic masses (eg, ganglionic cysts, schwannoma).



• Lack of or loss of the fat pad over the fibular head due to sudden weight loss and/or a thin body habitus predisposes the nerve to external compression at this site.



• The peroneal nerve, if tethered where it dives into the peroneus longus muscle, also may be damaged by stretch injury. Causes include prolonged squatting or a sudden stretch.



• Other conditions that mimic peroneal mononeuropathy include the following:


• • Sciatic nerve lesions involving predominantly the peroneal division are difficult to distinguish clinically. If the foot drop is associated temporally with hip surgery or trauma, then it is more likely to be due to sciatic nerve involvement.
  
  
  
• Generalized neuropathy can present with slowly progressive, bilateral foot drop but also is associated with plantar flexion weakness and stocking-distribution sensory loss.



• Clinically, the peroneal nerve may appear to be involved selectively in vasculitis, chronic inflammatory demyelinating neuropathy, or hereditary neuropathy with liability to pressure palsy. However, nerve conduction studies showing a more generalized or multifocal neuropathy may aid in the diagnosis.



• L5 radiculopathy also can present with a foot drop but can be distinguished clinically from a peroneal mononeuropathy by involvement of the foot inverters.

DIFFERENTIALS

Section 4 of 9

Diabetic Neuropathy
HIV-1 Associated Multiple Mononeuropathies
Leptomeningeal Carcinomatosis
Nutritional Neuropathy
Polyarteritis Nodosa
Sarcoidosis and Neuropathy
Systemic Lupus Erythematosus
Toxic Neuropathy
Traumatic Peripheral Nerve Lesions
Uremic Neuropathy
Vasculitic Neuropathy

Other Problems to be Considered:

Generalized peripheral neuropathy of any cause
Sciatic nerve lesions
Lumbosacral plexus lesions
Lumbosacral disk syndromes
Metabolic neuropathy
Paraneoplastic neuropathy
Paraproteinemic neuropathy

WORKUP

Section 5 of 9

Imaging Studies:

• MRI of the lower thigh or popliteal fossa may be indicated if a mass lesion is suspected.

Other Tests:

• Nerve conduction studies and needle EMG aid in defining the location and type of lesion.


• • Nerve conductions should show isolated peroneal nerve abnormalities. If the lesion is at the knee, then conduction block or, less commonly, conduction velocity slowing over that segment of the nerve should be documented. When axonal loss occurs in direct nerve trauma or with long-standing compression, a small compound muscle action potential may be noted. If other mononeuropathies with conduction blocks are found, then consideration should be made for an underlying vasculitis causing mononeuritis multiplex or possibly for hereditary neuropathy with liability to pressure palsy. If more diffuse nerve abnormalities are noted, then a generalized neuropathy should be considered, especially chronic demyelinating polyneuropathy.
  
  
  
  • EMG is useful to localize the lesion. It can be helpful in determining which nerve is involved primarily—the common peroneal nerve at the knee or one of its two branches, the superficial or deep peroneal nerve. The tibialis anterior or extensor hallicus longus muscles (ie, innervated by the deep peroneal) and the peroneus longus or brevis muscles (ie, innervated by the superficial peroneal) are useful to study for this purpose.
  
  
  
  • EMG also is helpful in determining if the foot drop is due to an L5 radiculopathy or a sciatic lesion. In an L5 radiculopathy, the tibialis posterior, which is a foot inverter, and the lumbosacral paraspinous muscles are involved.
  
  
  
  • Involvement of the peroneal division of the sciatic nerve in the thigh or hip area is more difficult to determine clinically. In the thigh, the peroneal division of the sciatic nerve innervates the short head of the biceps femoris muscle, a knee flexor. As isolating this muscle clinically is difficult, EMG may be necessary to determine involvement.
  
  
  
  • If lesions in the thigh are suspected on EMG, then MRI of the thigh (evaluating for cysts or tumors) is indicated.
  
  
  

TREATMENT

Section 6 of 9

Medical Care: Most peroneal nerve lesions respond to conservative management with rest and elimination of triggering factors such as leg crossing. Physical therapy is helpful in recovery of function. Additionally, ankle foot orthosis (AFO) helps to stabilize the gait and prevent tripping due to the foot drop.

Surgical Care: Evaluation for surgical intervention is rarely necessary except in the following situations:

• The lesion is due to a mass compressing the nerve.



• Release of nerve tethering is indicated.



• Severe or complete transection is suspected as with blunt or open trauma.

TEST QUESTIONS

Section 7 of 9

CME Question 1: How is an L5 radiculopathy distinguished from a peroneal mononeuropathy on examination?

A: Foot dorsiflexion
B: Foot inversion
C: Foot eversion
D: Numbness of the lateral calf
E: Numbness of the foot

The correct answer is B: Like peroneal mononeuropathy, L5 radiculopathy produces a foot drop, but the foot invertors (spared with peroneal lesions) are also weak. L5 radiculopathies also are associated with low back pain and radicular symptoms. The numbness associated with both lesions is over the lateral calf and the medial dorsal foot.

CME Question 2: Peroneal neuropathies are not associated with which of the following?

A: Short leg casts
B: Habitual leg crossing
C: Surgical positioning
D: Popliteal cysts
E: Obesity

The correct answer is E: A thin habitus or rapid weight loss is associated with peroneal nerve lesions because of loss or lack of the fat pad over the fibular head, which makes the nerve even more superficial at this level and more susceptible to trauma or compression.

Pearl Question 1 (T/F): The most common location of the lesion in a peroneal neuropathy is deep in the calf.

The correct answer is False: The most common site of damage to the peroneal nerve is as it wraps around the neck of the fibula in the lower leg. Here, it is superficial and highly susceptible to trauma.

Pearl Question 2 (T/F): A high sciatic lesion can be easily distinguished clinically from a peroneal neuropathy.

The correct answer is False: Nerve conduction studies and needle electromyography (EMG) often are required to distinguish a sciatic lesion involving the peroneal division from a peroneal nerve lesion at the knee. If the lesion is in the thigh or higher (ie, sciatic lesion), the short head of the biceps femoris is found to be involved on EMG. This muscle is difficult to isolate clinically. If the sciatic is involved more completely, weakness of tibial nerve–innervated muscles (eg, gastrocnemius) also may be noted.

Pearl Question 3 (T/F): Trauma is the most common cause of an isolated peroneal neuropathy.

The correct answer is True: Prolonged external pressure such as that caused by habitual leg crossing is the most common etiology of a peroneal nerve lesion.

Pearl Question 4 (T/F): The distribution of numbness associated with a common peroneal nerve lesion usually involves the fifth toe.

The correct answer is False: The numbness associated with a common peroneal nerve lesion is over the anterolateral lower calf and dorsum of the foot, sparing the fifth toe.

PICTURES

Section 8 of 9

Caption: Picture 1. Peroneal sensory distribution: The striped area is the superficial peroneal sensory distribution. The green solid area represents the deep peroneal sensory distribution. All 3 areas shaded would be numb in a patient with a common peroneal nerve lesion.
	View Full Size Image
	eMedicine Zoom View (Interactive!)
Picture Type: Photo

BIBLIOGRAPHY

Section 9 of 9

• Campbell WW: Focal Neuropathies. Essentials of electrodiagnostic medicine 1999; 255-278.
• Katirji B: Peroneal neuropathy. Neurol Clin 1999 Aug; 17(3): 567-91, vii[Medline].
• Katirji B, Wilbourn AJ: High sciatic lesion mimicking peroneal neuropathy at the fibular head. J Neurol Sci 1994 Feb; 121(2): 172-5[Medline].
• Marciniak C, Armon C, Wilson J: Practice parameter: utility of electrodiagnostic techniques in evaluating patients with suspected peroneal neuropathy: an evidence-based review. Muscle Nerve 2005 Apr; 31(4): 520-7[Medline].
• Turner OA, Taslitz N, Ward S: Common peroneal nerve entrapment. Handbook of peripheral nerve entrapments 1990; 119-124.
• Wilbourn AJ: AAEE case report #12: Common peroneal mononeuropathy at the fibular head. Muscle Nerve 1986 Nov-Dec; 9(9): 825-36[Medline].
• Williams FH, Johns JS, Weiss JM, et al: Neuromuscular rehabilitation and electrodiagnosis. 1. Mononeuropathy. Arch Phys Med Rehabil 2005 Mar; 86(3 Suppl 1): S3-10[Medline].

eMedicine Journals > Neurology > Electromyography And Nerve Conduction Studies > Peroneal Mononeuropathy

Please email us with any comments you have on our new chapter format.

Author Information | Introduction | Clinical | Differentials | Workup | Treatment | Test Questions | Pictures | Bibliography