PERONEAL NERVE PALSY AND ITS ELECTROPHYSIOLOGICAL DIAGNOSIS

Transcription

1 PERONEAL NERVE PALSY AND ITS ELECTROPHYSIOLOGICAL DIAGNOSIS B. GHUGARE*, P. DAS**, M. CHITLE***, R. SINGH**** ABSTRACT Peroneal neuropathy is one of the most common focal neuropathies in lower limbs at all ages. Clinically patient presents with foot drop and sensory disturbance over lateral calf and dorsum of the foot. Such clinical presentation may be due to sciatic neuropathy, lumbosacral plexopathy, L5 radiculopathy etc. Electrophysiological evaluation i.e. nerve conduction studies and electromyography not only locate the level of lesion but also establishes pathophysiology and hence prognosis of the disorder. Fibular head so far is the most common site for peroneal nerve lesions as fibers are more vulnerable to compression at this site. In this article an attempt is made to overview the peroneal nerve palsy and its diagnosis by nerve conduction studies and electromyography. Key words : Peroneal neuropathy, foot drop, motor conduction study, conduction block. Introduction Peroneal neuropathy at fibular head is the most common entrapment neuropathy in lower limbs because peroneal nerve most superficial and vulnerable to injury at this site. Clinically patient presents with foot drop and sensory disturbance over lateral calf and dorsum of the foot. Foot drop is due to weakness in ankle dorsiflexion and eversion as tibialis anterior and extensor digitorum brevis muscle are involved respectively. However patients with sciatic neuropathy, lumbosacral plexopathy and L5 radiculopathy may mimic clinically. Therefore electro diagnostic studies, in addition to establishing a diagnosis can also locate level of lesion and give prognostic information 1, 2. Other sites of focal neuropathies apart from those at fibular head that have been reported to cause peroneal palsy are at the level of calf, ankle, and foot 3. This review highlights the importance and limitations of electro diagnostic(ed) techniques in peroneal palsy evaluation. Anatomical perspective Fibers from L4, L5, S1 nerve roots travel through lumbosacral plexus that eventually turns into sciatic nerve with medial and lateral trunks. Medial trunk gives rise to tibial nerve and lateral trunk to common peroneal nerve. Short head of biceps femoris is the only muscle innervated by peroneal fibers above the popliteal fossa. First branch below popliteal fossa is lateral cutaneous nerve of calf, which supplies anterior, lateral, and * Assis. Prof., Dept of Physiology ACPM Medical College Dhule ** Assis. Prof., Dept of Physiology National Medical College Kolkata *** Prof. Dept. of Physiology ACPM Medical College Dhule **** Prof. & Head Dept. of Physiology MGIMS, Sevagram Wardha Author for correspondence and requests of reprints : Ramji Singh, Prof & Head, Dept of Physiology, MGIMS Sevagram, Wardha

2 posterior surface of leg. Common peroneal nerve then winds around the neck of fibula and passes through fibular tunnel and then divides into superficial and deep peroneal nerves. Superficial peroneal nerve innervates peroneus longus, peroneus brevis, and then supplies the lateral and dorsal portion of lower leg and dorsum of foot. Deep peroneal nerve supplies the muscles of anterior compartment, i.e. tibialis anterior (TA), extensor hallucis longus, extensor digitorum longus, extensor digitorum brevis (EDB) and peroneus tertius muscles, and its terminal branch innervates the skin web between the first and second toes 1, 4. Causes of peroneal nerve palsy The common peroneal nerves are vulnerable to external compression in its course around the head of fibula. Acute peroneal neuropathy often results from trauma or immobilization for prolonged periods. Slow progressive lesions are often due to mass such as ganglion or nerve sheath tumor. Habitual leg crossing, repetitive stretching from squatting position has been associated with peroneal neuropathy. Among systemic disorders diabetes mellitus (DM), leprosy is known to affect this nerve. Iatrogenic and idiopathic causes also add to this list 4,2. In 2000, Garozzo et al. reported five cases of peroneal neuropathy due to ankle sprain 5. Clinical Evaluation History of altered ambulation and loss of sensation in the cutaneous distribution of the superficial and deep peroneal nerves may be noted. Tapping of nerve at fibular head may produce positive Tinnel's sign. Examination often reveals a variable pattern of weakness of EDB and TA leading to ankle, toe dorsiflexion weakness. Ankle eversion may or may not be affected. In pure peroneal neuropathy, ankle inversion and plantar flexion should be spared. Steppage gait pattern may be observed due to excessive lifting of foot from the ground in order to clear the foot. Short head of biceps femoris often spared if neural insult is at or below knee. Patient history and clinical examination are the most important initial clinical tools to reach the diagnosis of strongly suspected peroneal neuropathy. Plain radiographs may be helpful in excluding fractures and osseous tumors. Metabolic and hematological studies may give some clue about certain systemic disorders like DM, hyperthyroidism, polyarteritis nodosa, alcoholic Polyneuropathy. It is better to evaluate the palsy through neurophysiological procedures, which can localize the lesion, reveal the pathophysiology, and establish the prognosis 1,6.

3 Electrophysiological Evaluation Recommended Nerve Conduction Study (NCS) Protocol Routine studies: 1. Peroneal motor study, recording EDB, stimulating ankle, below fibular head and lateral popliteal fossa. 2. If no focal slowing or conduction block is observed at fibular neck, perform peroneal motor conduction study, recording TA, stimulating below fibular head and lateral popliteal fossa. 3. Tibial motor study, recording abductor hallucis brevis, stimulating medial ankle and popliteal fossa. 4. Superficial peroneal sensory study, recording lateral ankle, stimulating lateral calf. 5. Sural sensory study, recording posterior ankle, stimulating calf. 6. Tibial and peroneal F responses. Note : if any study is abnormal or borderline always compare with contra lateral asymptomatic side; especially compound muscle action potentials (CMAPs) and sensory nerve action potentials (SNAPs) amplitudes. able I : How to localize the lesion site in foot drop on NCS-EMG findings? EMG findings Deep Peroneal Nerve Common peroneal Nerve Sciatic nerve Lumbosacral plexus L5 radical Tibialis Anterior Extensor hallucis longus Peroneus Longus Tibialis Posterior Flexor Digitorum longus Short head (bicep femoris) Gluteus medius Tensor fascia lata Paraspinal muscles NCS findings Abnormal peroneal SNAP

4 Abnormal sural SNAP Low peroneal v CMAP Low tibial CMAP Abnormal H reflex Conduction block- fibular neck(if demyelinatin) 0 - may be abnormal if lesion involves S1 fibers as well. ; - Abnormalities may be present.; CMAP - compound muscle action potential; SNAP - sensory nerve action potential; NCS - nerve conduction study; EMG - electromyography Recommended Needle Electromyography (EMG) protocol Routine muscles: 1. At least two muscles innervated by deep peroneal nerve (e.g. Tibialis anterior, extensor hallucis longus). 2. At least one muscle innervated by the superficial peroneal nerve (e.g. peroneus longus, peroneus brevis). 3. Tibialis posterior and one other muscle innervated by tibial nerve e.g. medial head of gastroenemius. 4. Short head of biceps femoris. Note : In case of borderline findings in a muscle, compare with contra lateral side. If short head of biceps femoris or any tibial innervated muscle is abnormal or if NCS findings are nonspecific, go for extensive needle EMG of sciatic, gluteal, and paraspinal muscles to identify the level of lesion 1. Short head of biceps femoris has an important role in suspected peroneal neuropathy at the fibular neck as it is the only peroneal innervated muscle above fibular neck. Abnormal EMG findings to locate the lesion in foot drop are given in Table no. 1. Information gained by needle EMG is derived by spontaneous and voluntary activity. The presence of spontaneous activity represents neurogenic lesion. Evaluation of voluntary activity consists of assessment of amplitude,

5 shape, duration of individual motor unit potentials (MUPs) and its recruitment pattern called as interference pattern (IP) 7. Pathophysiology and prognosis Determining the underlying pathophysiology is very important in assessing the prognosis. In general, prognosis for a demyelinating lesion is much more favorable than for an axonal loss lesion. Segmental nerve conduction studies across the fibular neck are best in assessing the demyelinating pathophysiology. In demyelination, there is evidence of conduction block and slowing across the lesion. The number of axons that have undergone degeneration can be roughly estimated by comparing the CMAP amplitude on contra lateral asymptomatic side 6. In demyelination, underlying axons remain intact, and the repair process consists of only remyelination over period of weeks whereas in axonopathy, recovery requires the regeneration of terminal axon or collateral sprouting from spared axons over period of several months to a year or more. Hence in former type, functional recovery is fast within a month or two while later takes longer period of one or more years 4. Summary and Recent trends An evidence based review, in patients with suspected peroneal neuropathy, following ED studies are possibly useful, to make or confirm the diagnosis 8, 9 : 1. NCS a) Motor NCS of peroneal nerve recording from the TA & EDB muscles, including segmental nerve conduction along fibular neck (Level C recommendation, Class III evidence); b) Orthodromic and antidromic superficial peroneal sensory NCS (Level C recommendation, Class III evidence); c) At least one additional normal motor and sensory NCS in the same limb, to assure that the peroneal neuropathy is isolated, and not part of a more widespread local or systemic neuropathy. 2. Data are insufficient to determine the role of needle EMG in making the diagnosis of peroneal neuropathy (Class IV evidence). 3. In patients with confirmed peroneal neuropathy, ED studies are possibly useful in providing prognostic information, with regards to recovery of function (Level C recommendation, Class III & IV evidence)

6 Current article reviewed the role of ED studies in evaluation of patients with suspected peroneal nerve palsy. Most of the previous studies only provided class III and class IV evidence, resulting in conservative assessment of their utility. CMAPs recording from Extensor digitorum brevis CMAPs recording from Tibialis anterior References 1. Preston DC, Shapiro BE: Peroneal Nerve Palsy. In: Preston DC, Shapiro BE eds, Electromyography and neuromuscular disorders : Clinical- Electrophysiologic Correlations 2 nd ed, Philadelphia, Elsevier 2005: Misra UK, Kalita J: Sacral plexus and its terminal nerve branches. In: Misra UK, Kalita J eds, Clinical Neurophysiology 2 nd ed, New Delhi, Elsevier 2005: Oh SJ, Demirei M, Dajani B, Melo AC, Claussen GC: Distal sensory nerve conduction of the superficial peroneal nerve: new method and its clinical application. Muscle Nerve 2001; 24:

7 4. Kimura J: Mononeuropathies and entrapment syndromes. In: Kimura J eds, Electrodiagnosis in Diseases of Nerve and Muscle 3 rd ed, New York, Oxford University Press 2001: Garozzo D, Ferraresi S, Buffatti P: Common peroneal nerve palsy complicating ankle sprain: report of five cases and review of literature. J Orthopaed Traumatol 2003; 4: Gilchrist JM, Sachs GM: Electrodiagnostic studies in the management and prognosis of neuromuscular disorders. Muscle Nerve 2004; 29: Sonoo M: new attempts to quantify concentric needle electromyography. Muscle Nerve 2002; S11:S98-S Merciniak C, Armon C, Wilson J, Millar R: Practice parameter: utility of electrodiagnostic techniques in evaluating patients with suspected peroneal neuropathy: an evidence-based review. Muscle Nerve 2005; 31: Yoshihisa M, Michiyuki K, KanjiroS, Leon A, Tetsuo O, Akio K: Clinical Neurophysiology in the Diagnosis of Peroneal Nerve Palsy. Keio J Med 2008;57(2):84-89.