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Atypical Presentations of Common Peroneal Neuropathy
Clinical Pearl
Atypical Presentations of Common Peroneal Neuropathy Thiru M. Annaswamy, MD, MA, Hai-Yan Li, MD INTRODUCTION Common peroneal neuropathy (CPN) can mimic lumbar radiculopathy both clinically and electrodiagnostically [1]. CPN caused by entrapment at the fibular head is the most frequent mononeuropathy of the lower limb [1]. The superficial peroneal sensory (SPS) nerve conduction study (NCS) is performed frequently in persons with suspected CPN. A normal SPS response often is used to differentiate radiculopathy from CPN. However, CPN at the fibular head can preferentially affect superficial peroneal motor fibers while sparing the SPS branches, making it difficult to differentiate it from L5 radiculopathy [1]. This finding is consistent with the concept of selective fascicular involvement in peripheral nerve lesions [1-3]. The 2 cases presented involve patients who had CPN with spared SPS fibers on electrodiagnostic testing (EDX), an uncharacteristic and atypical presentation. It is important to perform EDX to accurately diagnose such atypical CPN lesions, and especially to differentiate them from their common mimicker, L5 radiculopathy.
CASE PRESENTATIONS Case 1 A 53-year-old man experienced sudden-onset, right-sided low back pain, right leg pain, and foot pain with dorsal and medial foot numbness after a prolonged stretching exercise. He had progressive right foot weakness and difficulty walking during gait assessment. Examination revealed right foot drop. Manual muscle testing revealed 2/5 strength in the right ankle dorsiflexors (ADF), ankle evertors, and long toe extensors (LTE). The distal aspect of the lateral leg and dorsal aspect of the foot revealed decreased sensation to light touch and pin prick. EDX revealed absent right peroneal motor responses at both extensor digiti brevis and tibialis anterior (TA) recorded with surface electrodes. Right tibial and left peroneal motor NCS revealed normal findings (Table 1). Bilateral SPS and right sural responses were normal. Needle electromyography (NEE) revealed denervation changes only in the right peroneal innervated muscles (Table 2). The diagnosis of a severe right CPN affecting the deep peroneal and superficial peroneal motor fibers while sparing the SPS fibers was made. Magnetic resonance imaging (MRI) of the lumbar spine demonstrated a broad-based disk bulge with facet hypertrophy and right greater than left foraminal encroachment at L4-5 and left paracentral disk bulge without foraminal encroachment at L5-S1. MRI of the right leg showed no peroneal nerve abnormalities at or about fibular head.
Case 2 A 53-year-old man presented with a 6-month history of sudden onset of lumbago and pain below his right lateral leg, followed shortly by a foot drop. Initial examination 3 weeks after the onset of symptoms revealed 5/5 muscle strength in all the muscles in the right lower limb except for 2/5 in the ADF and 3/5 in the right LTE. Sensation was abnormal in the right L5 distribution, and straight leg raise was positive on the right. Lumbar MRI showed a large herniated disk at lumbar 4-5 compressing the right L5 nerve root. Diagnosis of an L5 radiculopathy without proximal muscle involvement was made, and the patient underwent urgent decompression laminectomy and diskectomy. Six months after surgery, he had PM&R
462
1934-1482/12/$36.00 Printed in U.S.A.
T.M.A. PM&R Service, Dallas VA Medical Center, North Texas Health Care System, 4500 South Lancaster Rd, Dallas, TX 75216 and Department of PM&R, UT Southwestern Medical Center, Dallas, TX. Address correspondence to: T.M.A.; e-mail: [email protected] Disclosure: nothing to disclose H.-Y.L. Department of Physical Medicine and Rehabilitation, UT Southwestern Medical Center, Dallas, TX, and The Division of Pain Management, Stanford University Medical Center, Palo Alto, CA Disclosure: nothing to disclose Disclosure Key can be found on the Table of Contents and at www.pmrjournal.org Submitted for publication November 2, 2011; accepted March 24, 2012.
© 2012 by the American Academy of Physical Medicine and Rehabilitation Vol. 4, 462– 465, June 2012 http://dx.doi.org/10.1016/j.pmrj.2012.03.019
PM&R
Vol. 4, Iss. 6, 2012
463
Table 1. Case 1 motor and sensory nerve conduction studies Nerve and Site
Latency, ms
Amplitude, mV
NR* NR* NR*
Right peroneal (EDB) Ankle Fibula head Popliteal fossa Right peroneal (TA) Fibula head Popliteal fossa Left peroneal (EDB) Ankle Fibula head Popliteal fossa Right tibial (AH) Ankle Popliteal fossa Right superficial peroneal Right sural Left superficial peroneal
Amplitude, v
Distance, cm
Velocity, m/s
NR* NR* NR*
NR* NR* NR*
NR* NR* NR*
NR* NR*
NR* NR*
NR* NR*
NR* NR*
4.4 10 12.7
4.2 4.3 3.8
9 28 11
50 41
5.5 14.4 3.6 3.6 3.4
10.9 8.9
9 41 14 14 14
6.9 16.8 9.3
46
EDB ⫽ extensor digitorum brevis; NR ⫽ no response; TA ⫽ tibialis anterior; AH ⫽ abductor hallucis. All responses were recorded with the use of surface electrodes. *Abnormal values.
minimal improvement in ADF and LTE strength and required a brace for right foot drop, although his lumbago had resolved. Manual muscle testing revealed 0/5 ADF, 2/5 LTE, and 4/5 ankle evertors. Sensory examination revealed decreased sensation over the great toe. An EDX evaluation was performed 6 months after surgery. Right peroneal motor NCS to extensor digiti brevis revealed no response (Table 3). SPS response was normal. Right peroneal motor NCS to TA showed a severely decreased distal compound muscle action potential amplitude and a further drop in amplitude with proximal stimulation, markedly prolonged proximal response latency indicating focal slowing, conduction block, and axonal loss. NEE revealed acute denervation changes with large fibrillations and positive sharp waves in the TA and peroneus longus, in addition to some evidence of reinnervation (Table 4). The medial gastrocnemius revealed some evidence of mild reinnervation without any ongoing denervation findings such as fibrillations or positive sharp waves. Because fibrillations and positive sharp waves were noted in the peroneal innervated
muscles only and not in the gastrocnemius (which showed evidence of chronic reinnervation only), it was concluded that the common peroneal nerve was afflicted with an acute, ongoing axonal injury. A final diagnosis of double crush syndrome was made with acute CPN at the fibular neck with focal demyelination and severe axonal loss affecting the deep peroneal and superficial peroneal motor fibers while sparing the SPS fibers, in addition to a chronic L5-S1 radiculopathy.
DISCUSSION Electrodiagnostic localization of a peripheral nerve lesion is traditionally based on the peripheral neuroanatomy. It often is assumed that the lesion lies between the unaffected proximal nerve branches and the affected distal ones. This assumption is true in complete nerve injuries and in partial nerve lesions when fascicles are equally affected. However, this simple approach, based on the anatomy of nerve branches, can be extremely misleading in cases of partial nerve damage [4]. Studies have shown that sensory nerve
Table 2. Case 1 needle electrode examination Muscle R R R R R R R
tibialis anterior peroneus longus medial gastrocnemius biceps femoris SH Biceps femoris LH gluteus medius lumbar paraspinal
IA
Fibs/PS
HF
Poly
Amp
Dur
Rec
Inc* Inc* Nml Nml Nml Nml Nml
4⫹* 2⫹* — — — — —
1⫹* — — — — — —
2⫹ * — — — — —
1⫹* Nml Nml Nml Nml Nml
2⫹* Nml Nml Nml Nml Nml
Dec* Dec* Nml Nml Nml Nml
IA ⫽ insertional activity; Fibs/PS ⫽ fibrillations/positive sharps; HF ⫽ high frequency; Poly ⫽ polyphasics; Amp ⫽ amplitude; Dur ⫽ duration; Rec ⫽ recruitment; R ⫽ right; Inc ⫽ increased; Dec ⫽ decreased; Nml ⫽ normal; SH ⫽ short head; LH ⫽ long head. *Abnormal values.
464
Annaswamy and Li
ATYPICAL PRESENTATIONS OF CPN
Table 3. Case 2 motor and sensory nerve conduction studies Nerve and Site R peroneal (EDB) Ankle Fibula head Popliteal fossa R peroneal (TA) Fibula head Popliteal fossa R tibial (AH) Ankle Popliteal fossa L Peroneal (EDB) Ankle Fibula head Popliteal fossa L peroneal (TA) Fibula head Popliteal fossa L tibial (AH) Ankle Popliteal fossa R superficial peroneal R Sural L superficial peroneal L sural
Latency, ms
Amplitude, mV
NR* NR* NR* 2.95 16.1
Amplitude, v
Distance, cm
Velocity, m/s
NR* NR* NR*
NR* NR* NR*
NR* NR* NR*
0.8* 0.2*
10 8
6.1
8 40
37.9
5.75 16.30
14.5 11.9
4.80 11.25 13.75
6.0 6.1 5.9
8 27.5 11
42.6 44
2.85 4.35
8.0 8.3
10 11
73.3
3.6 13.55 3.55 4.2 3.95 4.3
15.2 12
8 39 14 14 14 14
9.8 9.7 9.3 8.6
39.2
R ⫽ right; EDB ⫽ extensor digitorum brevis; NR ⫽ no response; L ⫽ left; TA ⫽ tibialis anterior; AH ⫽ abductor hallucis. All responses were recorded with the use of surface electrodes. *Abnormal values.
fibers supplying sensation to specific skin areas and motor fibers innervating specific muscles tend to remain grouped together as fascicles or within fascicles throughout much of their course in the nerve [4,5]. Selective involvement of these fascicles in persons with partial nerve damage may produce restricted neurological deficits, which can lead to inaccurate localization of a lesion to a more distal site than the actual site if it is based on a standard electrodiagnostic approach. The phenomenon of selective fascicular involve-
ment has been demonstrated in many focal mononeuropathies, including CPN [1,2,4]. In CPN, it is well documented that muscles supplied by the deep peroneal nerve are more frequently and severely affected than those supplied by superficial peroneal nerve [3]. Our cases demonstrated another atypical pattern of CPN presentation with involvement of superficial peroneal motor fibers and sparing of its sensory fibers. This unusual CPN presentation can be explained by selective fascicular involve-
Table 4. Case 2 needle electrode examination
R R R R R R R R R R R R
Muscle
IA
Fibs/PS
tibialis anterior peroneus longus med. gastrocnemius biceps femoris SH biceps femoris LH gluteus medius posterior tibialis vastus lateralis rectus femoris adductor longus semimembranosus lumbar paraspinals
Inc* Inc* Nml Nml Nml Nml Nml Nml Nml Nml Nml
2⫹* 2⫹* — — — — — — — — —
HF
Poly
Amp
— — 2⫹* 1⫹* 2⫹* — 1⫹* Nml — — Nml — — Nml — — Nml — — Nml — — Nml — — Nml — — Nml — — Nml Not performed because of recent surgery
Dur
Rec
No Motor Unit 1⫹* 1⫹* Nml Nml Nml Nml Nml Nml Nml Nml
Dec* Nml Nml Nml Nml Nml Nml Nml Nml Nml
IA ⫽ insertional activity; Fibs/PS ⫽ fibrillations/positive sharps; HF ⫽ high frequency; Poly ⫽ polyphasics; Amp ⫽ amplitude; Dur ⫽ duration; Rec ⫽ recruitment; R ⫽ right; Inc ⫽ increased; Dec ⫽ decreased; Nml ⫽ normal; SH ⫽ short head; LH ⫽ long head. *Abnormal values.
PM&R
ment of motor fibers in CPN [1,2]. The cause of the variable involvement or susceptibility of selective fascicles is uncertain. It has been suggested that the fascicles nearest the bone might sustain greater pressures from compression. Perhaps some fascicles may have less “protective” connective tissue covering as well [4].
CLINICAL PEARL It is important to recognize an atypical pattern of CPN with spared superficial peroneal sensory response, as described in our cases, to avoid misdiagnosing CPN as lumbar radiculopathy. This situation is true particularly in cases in which 2 sites of nerve impingement might coexist (case 2 had dual nerve impingement at the fibular head and proximally at the lumbar root level). Evidence of focal demyelination of the peroneal nerve at the fibular head on NCS and abnormal NEE
Vol. 4, Iss. 6, 2012
465
findings confined to common peroneal innervated muscles while sparing nonperoneal innervated but L5 innervated muscles allows one to differentiate between these 2 diagnoses.
REFERENCES 1. Kang P, Preston D, Raynor E. Involvement of superficial peroneal sensory nerve in common peroneal neuropathy. Muscle Nerve 2005;31:725729. 2. de Carvalho M, Miguel S, Bentes C. Sensory potential can be preserved in severe common peroneal neuropathy. Electromyogr Clin Neurophysiol 2000;40:61-63. 3. Sourkes M, Stewart J. Common peroneal neuropathy: A study of selective motor and sensory involvement. Neurology 1991;41:1029-1033. 4. Stewart J. Peripheral nerve fascicles: Anatomy and clinical relevance. Muscle Nerve 2003;28:525-541. 5. Hallin R. Microneurography in relation to intraneural topography: Somatotopic organisation of median nerve fascicles in humans. J Neurol Neurosurg Psychiatry 1990;53:736-744.
Atypical Presentations of Common Peroneal Neuropathy Thiru M. Annaswamy, MD, MA, Hai-Yan Li, MD INTRODUCTION Common peroneal neuropathy (CPN) can mimic lumbar radiculopathy both clinically and electrodiagnostically [1]. CPN caused by entrapment at the fibular head is the most frequent mononeuropathy of the lower limb [1]. The superficial peroneal sensory (SPS) nerve conduction study (NCS) is performed frequently in persons with suspected CPN. A normal SPS response often is used to differentiate radiculopathy from CPN. However, CPN at the fibular head can preferentially affect superficial peroneal motor fibers while sparing the SPS branches, making it difficult to differentiate it from L5 radiculopathy [1]. This finding is consistent with the concept of selective fascicular involvement in peripheral nerve lesions [1-3]. The 2 cases presented involve patients who had CPN with spared SPS fibers on electrodiagnostic testing (EDX), an uncharacteristic and atypical presentation. It is important to perform EDX to accurately diagnose such atypical CPN lesions, and especially to differentiate them from their common mimicker, L5 radiculopathy.
CASE PRESENTATIONS Case 1 A 53-year-old man experienced sudden-onset, right-sided low back pain, right leg pain, and foot pain with dorsal and medial foot numbness after a prolonged stretching exercise. He had progressive right foot weakness and difficulty walking during gait assessment. Examination revealed right foot drop. Manual muscle testing revealed 2/5 strength in the right ankle dorsiflexors (ADF), ankle evertors, and long toe extensors (LTE). The distal aspect of the lateral leg and dorsal aspect of the foot revealed decreased sensation to light touch and pin prick. EDX revealed absent right peroneal motor responses at both extensor digiti brevis and tibialis anterior (TA) recorded with surface electrodes. Right tibial and left peroneal motor NCS revealed normal findings (Table 1). Bilateral SPS and right sural responses were normal. Needle electromyography (NEE) revealed denervation changes only in the right peroneal innervated muscles (Table 2). The diagnosis of a severe right CPN affecting the deep peroneal and superficial peroneal motor fibers while sparing the SPS fibers was made. Magnetic resonance imaging (MRI) of the lumbar spine demonstrated a broad-based disk bulge with facet hypertrophy and right greater than left foraminal encroachment at L4-5 and left paracentral disk bulge without foraminal encroachment at L5-S1. MRI of the right leg showed no peroneal nerve abnormalities at or about fibular head.
Case 2 A 53-year-old man presented with a 6-month history of sudden onset of lumbago and pain below his right lateral leg, followed shortly by a foot drop. Initial examination 3 weeks after the onset of symptoms revealed 5/5 muscle strength in all the muscles in the right lower limb except for 2/5 in the ADF and 3/5 in the right LTE. Sensation was abnormal in the right L5 distribution, and straight leg raise was positive on the right. Lumbar MRI showed a large herniated disk at lumbar 4-5 compressing the right L5 nerve root. Diagnosis of an L5 radiculopathy without proximal muscle involvement was made, and the patient underwent urgent decompression laminectomy and diskectomy. Six months after surgery, he had PM&R
462
1934-1482/12/$36.00 Printed in U.S.A.
T.M.A. PM&R Service, Dallas VA Medical Center, North Texas Health Care System, 4500 South Lancaster Rd, Dallas, TX 75216 and Department of PM&R, UT Southwestern Medical Center, Dallas, TX. Address correspondence to: T.M.A.; e-mail: [email protected] Disclosure: nothing to disclose H.-Y.L. Department of Physical Medicine and Rehabilitation, UT Southwestern Medical Center, Dallas, TX, and The Division of Pain Management, Stanford University Medical Center, Palo Alto, CA Disclosure: nothing to disclose Disclosure Key can be found on the Table of Contents and at www.pmrjournal.org Submitted for publication November 2, 2011; accepted March 24, 2012.
© 2012 by the American Academy of Physical Medicine and Rehabilitation Vol. 4, 462– 465, June 2012 http://dx.doi.org/10.1016/j.pmrj.2012.03.019
PM&R
Vol. 4, Iss. 6, 2012
463
Table 1. Case 1 motor and sensory nerve conduction studies Nerve and Site
Latency, ms
Amplitude, mV
NR* NR* NR*
Right peroneal (EDB) Ankle Fibula head Popliteal fossa Right peroneal (TA) Fibula head Popliteal fossa Left peroneal (EDB) Ankle Fibula head Popliteal fossa Right tibial (AH) Ankle Popliteal fossa Right superficial peroneal Right sural Left superficial peroneal
Amplitude, v
Distance, cm
Velocity, m/s
NR* NR* NR*
NR* NR* NR*
NR* NR* NR*
NR* NR*
NR* NR*
NR* NR*
NR* NR*
4.4 10 12.7
4.2 4.3 3.8
9 28 11
50 41
5.5 14.4 3.6 3.6 3.4
10.9 8.9
9 41 14 14 14
6.9 16.8 9.3
46
EDB ⫽ extensor digitorum brevis; NR ⫽ no response; TA ⫽ tibialis anterior; AH ⫽ abductor hallucis. All responses were recorded with the use of surface electrodes. *Abnormal values.
minimal improvement in ADF and LTE strength and required a brace for right foot drop, although his lumbago had resolved. Manual muscle testing revealed 0/5 ADF, 2/5 LTE, and 4/5 ankle evertors. Sensory examination revealed decreased sensation over the great toe. An EDX evaluation was performed 6 months after surgery. Right peroneal motor NCS to extensor digiti brevis revealed no response (Table 3). SPS response was normal. Right peroneal motor NCS to TA showed a severely decreased distal compound muscle action potential amplitude and a further drop in amplitude with proximal stimulation, markedly prolonged proximal response latency indicating focal slowing, conduction block, and axonal loss. NEE revealed acute denervation changes with large fibrillations and positive sharp waves in the TA and peroneus longus, in addition to some evidence of reinnervation (Table 4). The medial gastrocnemius revealed some evidence of mild reinnervation without any ongoing denervation findings such as fibrillations or positive sharp waves. Because fibrillations and positive sharp waves were noted in the peroneal innervated
muscles only and not in the gastrocnemius (which showed evidence of chronic reinnervation only), it was concluded that the common peroneal nerve was afflicted with an acute, ongoing axonal injury. A final diagnosis of double crush syndrome was made with acute CPN at the fibular neck with focal demyelination and severe axonal loss affecting the deep peroneal and superficial peroneal motor fibers while sparing the SPS fibers, in addition to a chronic L5-S1 radiculopathy.
DISCUSSION Electrodiagnostic localization of a peripheral nerve lesion is traditionally based on the peripheral neuroanatomy. It often is assumed that the lesion lies between the unaffected proximal nerve branches and the affected distal ones. This assumption is true in complete nerve injuries and in partial nerve lesions when fascicles are equally affected. However, this simple approach, based on the anatomy of nerve branches, can be extremely misleading in cases of partial nerve damage [4]. Studies have shown that sensory nerve
Table 2. Case 1 needle electrode examination Muscle R R R R R R R
tibialis anterior peroneus longus medial gastrocnemius biceps femoris SH Biceps femoris LH gluteus medius lumbar paraspinal
IA
Fibs/PS
HF
Poly
Amp
Dur
Rec
Inc* Inc* Nml Nml Nml Nml Nml
4⫹* 2⫹* — — — — —
1⫹* — — — — — —
2⫹ * — — — — —
1⫹* Nml Nml Nml Nml Nml
2⫹* Nml Nml Nml Nml Nml
Dec* Dec* Nml Nml Nml Nml
IA ⫽ insertional activity; Fibs/PS ⫽ fibrillations/positive sharps; HF ⫽ high frequency; Poly ⫽ polyphasics; Amp ⫽ amplitude; Dur ⫽ duration; Rec ⫽ recruitment; R ⫽ right; Inc ⫽ increased; Dec ⫽ decreased; Nml ⫽ normal; SH ⫽ short head; LH ⫽ long head. *Abnormal values.
464
Annaswamy and Li
ATYPICAL PRESENTATIONS OF CPN
Table 3. Case 2 motor and sensory nerve conduction studies Nerve and Site R peroneal (EDB) Ankle Fibula head Popliteal fossa R peroneal (TA) Fibula head Popliteal fossa R tibial (AH) Ankle Popliteal fossa L Peroneal (EDB) Ankle Fibula head Popliteal fossa L peroneal (TA) Fibula head Popliteal fossa L tibial (AH) Ankle Popliteal fossa R superficial peroneal R Sural L superficial peroneal L sural
Latency, ms
Amplitude, mV
NR* NR* NR* 2.95 16.1
Amplitude, v
Distance, cm
Velocity, m/s
NR* NR* NR*
NR* NR* NR*
NR* NR* NR*
0.8* 0.2*
10 8
6.1
8 40
37.9
5.75 16.30
14.5 11.9
4.80 11.25 13.75
6.0 6.1 5.9
8 27.5 11
42.6 44
2.85 4.35
8.0 8.3
10 11
73.3
3.6 13.55 3.55 4.2 3.95 4.3
15.2 12
8 39 14 14 14 14
9.8 9.7 9.3 8.6
39.2
R ⫽ right; EDB ⫽ extensor digitorum brevis; NR ⫽ no response; L ⫽ left; TA ⫽ tibialis anterior; AH ⫽ abductor hallucis. All responses were recorded with the use of surface electrodes. *Abnormal values.
fibers supplying sensation to specific skin areas and motor fibers innervating specific muscles tend to remain grouped together as fascicles or within fascicles throughout much of their course in the nerve [4,5]. Selective involvement of these fascicles in persons with partial nerve damage may produce restricted neurological deficits, which can lead to inaccurate localization of a lesion to a more distal site than the actual site if it is based on a standard electrodiagnostic approach. The phenomenon of selective fascicular involve-
ment has been demonstrated in many focal mononeuropathies, including CPN [1,2,4]. In CPN, it is well documented that muscles supplied by the deep peroneal nerve are more frequently and severely affected than those supplied by superficial peroneal nerve [3]. Our cases demonstrated another atypical pattern of CPN presentation with involvement of superficial peroneal motor fibers and sparing of its sensory fibers. This unusual CPN presentation can be explained by selective fascicular involve-
Table 4. Case 2 needle electrode examination
R R R R R R R R R R R R
Muscle
IA
Fibs/PS
tibialis anterior peroneus longus med. gastrocnemius biceps femoris SH biceps femoris LH gluteus medius posterior tibialis vastus lateralis rectus femoris adductor longus semimembranosus lumbar paraspinals
Inc* Inc* Nml Nml Nml Nml Nml Nml Nml Nml Nml
2⫹* 2⫹* — — — — — — — — —
HF
Poly
Amp
— — 2⫹* 1⫹* 2⫹* — 1⫹* Nml — — Nml — — Nml — — Nml — — Nml — — Nml — — Nml — — Nml — — Nml Not performed because of recent surgery
Dur
Rec
No Motor Unit 1⫹* 1⫹* Nml Nml Nml Nml Nml Nml Nml Nml
Dec* Nml Nml Nml Nml Nml Nml Nml Nml Nml
IA ⫽ insertional activity; Fibs/PS ⫽ fibrillations/positive sharps; HF ⫽ high frequency; Poly ⫽ polyphasics; Amp ⫽ amplitude; Dur ⫽ duration; Rec ⫽ recruitment; R ⫽ right; Inc ⫽ increased; Dec ⫽ decreased; Nml ⫽ normal; SH ⫽ short head; LH ⫽ long head. *Abnormal values.
PM&R
ment of motor fibers in CPN [1,2]. The cause of the variable involvement or susceptibility of selective fascicles is uncertain. It has been suggested that the fascicles nearest the bone might sustain greater pressures from compression. Perhaps some fascicles may have less “protective” connective tissue covering as well [4].
CLINICAL PEARL It is important to recognize an atypical pattern of CPN with spared superficial peroneal sensory response, as described in our cases, to avoid misdiagnosing CPN as lumbar radiculopathy. This situation is true particularly in cases in which 2 sites of nerve impingement might coexist (case 2 had dual nerve impingement at the fibular head and proximally at the lumbar root level). Evidence of focal demyelination of the peroneal nerve at the fibular head on NCS and abnormal NEE
Vol. 4, Iss. 6, 2012
465
findings confined to common peroneal innervated muscles while sparing nonperoneal innervated but L5 innervated muscles allows one to differentiate between these 2 diagnoses.
REFERENCES 1. Kang P, Preston D, Raynor E. Involvement of superficial peroneal sensory nerve in common peroneal neuropathy. Muscle Nerve 2005;31:725729. 2. de Carvalho M, Miguel S, Bentes C. Sensory potential can be preserved in severe common peroneal neuropathy. Electromyogr Clin Neurophysiol 2000;40:61-63. 3. Sourkes M, Stewart J. Common peroneal neuropathy: A study of selective motor and sensory involvement. Neurology 1991;41:1029-1033. 4. Stewart J. Peripheral nerve fascicles: Anatomy and clinical relevance. Muscle Nerve 2003;28:525-541. 5. Hallin R. Microneurography in relation to intraneural topography: Somatotopic organisation of median nerve fascicles in humans. J Neurol Neurosurg Psychiatry 1990;53:736-744.