Common Entrapment Neuropathies

. 487 . Muscle & Nerve 2017 American Academy Address correspondence to Dr Lisa D. Hobson-Webb, Department of Neurology, Duke University Medical Center, DUMC 3403, Room 1255 EMG Laboratory, Durham, NC 27710, [email protected] Relationship Disclosure: Dr Hobson-Webb has served on the editorial boardClinical of Neurophysiology and as an associatefor editor Dr Hobson-Webb receives research/grant support from CSL Behring, the National Institute on Aging/Duke University Claude D. Pepper Older Americans Independence Center, and Sanofi Genzyme. Dr Juel receives research/ grant support as site investigator for studies for Alexion Pharmaceuticals, Inc and the Nationalof Institute Allergy and Infectious Diseases, Division of Microbiology and Infectious Diseases. Unlabeled Use of Products/Investigational Use Disclosure: Drs Hobson-Webb and Juel report no disclosures. * of Neurology. ContinuumJournal.com Morton neuroma, 2 3 Its prevalence in the Review Article 1,2 Knowing peripheral nerve anatomy median nerve.drome Carpal may tunnel beof present syn- in workers up(eg, in to poultry 42% certain processing)annual incidence occupations and of 193 has perall 100,000 an in women. and function allowstion that clinical canconfirmed localiza- with be electrodiagnostic further studies refined and and peripheralpatients nerve imaging. with In etiology, mononeuropathy, severity, odds of the spontaneous ulnar neuropathy, meralgia paresthetica, and radialthe neuropathy other represent mononeuropathies. most common peripheral United States is1000, estimated with ataffected 50 a individual. per cost of $30,000 per This article addresses relevant peripheral neuroanatomy, Entrapment neuropathies are a common issue in general neurology Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. Copyright © American Academy of Neurology. Unauthorized reproduction of this article is Entrapment neuropathies are commonly encountered in clinical practice. Hobson-Webb, MD; Vern C. Juel, MD, FAAN

Lisa D.

Entrapment mononeuropathies ABSTRACT Continuum (Minneap Minn) 2017;23(2):487–511. Accurate diagnosis andneuroanatomy effective and management recognitiondiagnoses require may of knowledge be keyand of confirmed peripheral clinical nerve peripheral by ultrasound. symptoms diagnostic testing and with findings. electrodiagnostic Clinical studies Purpose of Review: clinical presentations, and diagnostic findingsinvolving in the common median, entrapment ulnar, neuropathies Recent radial, Findings: and fibular (peroneal)practice. Early nerves. diagnosis and effective management ofare entrapment mononeuropathies essential in preserving limb function andneuropathy maintaining at patient quality the of wrist (carpal life. tunnel Median syndrome), ulnar neuropathyneuropathy at at the the elbow, radial spiral groove, and fibularthe neuropathy at most the fibular frequently head are encounteredstudies among entrapment and mononeuropathies. peripheral Electrodiagnostic nervediagnosis of ultrasound nerve are compression or employednerve entrapment to and injury. Peripheral to help nerve provide ultrasound precise confirmsites demonstrates localization of the nerve for compression. enlargement clinical at orSummary: near Continuum (Minneap Minn) 2017;23(2):487–511 represent a common reasonto for primary visits carerology practices. and The most outpatient commonthese, of neu- carpalrelated tunnel to chronic syndrome, compression of is the INTRODUCTION This article focusesmononeuropathies, on indicating peripheral ease dis- or dysfunction in a singleeral periph- nerve. Mononeuropathies may be caused by focal compression,mation, inflam- nerveother tumors, etiologies. trauma, Compressionentrapment) or is (or thecause. While most mononeuropathies may common also be superimposedground upon of a polyneuropathy, back- of a polyneuropathies survey isscope of beyond this article. the

Neuropathies Common Entrapment

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KEY POINT h Early diagnosis and recovery, and patient preferences MEDIAN NERVE effective management are important factors that guide Median neuropathy at the wrist, spe- of mononeuropathies treatment. Early diagnosis and ef- cifically carpal tunnel syndrome, is the are essential in improving fective management of mononeuro- most common mononeuropathy of patient quality of life and pathies are essential in improving adults. A thorough understanding of reducing costs of care. patient quality of life and reducing the anatomy of the median nerve and costs of care. adjacent structures and of associated This article presents the most com- diagnostic techniques is therefore in- monly encountered entrapment mono- valuable in outpatient neurology. neuropathies, with a focus on relevant anatomy, clinical symptoms, methods Basic Anatomy of diagnosis, and recommended The median nerve forms from the treatment. The pathophysiologic pro- terminal divisions of the medial and cesses related to peripheral nerve lateral cords of the brachial plexus, trauma and compression are not receiving contributions from the C5 to covered in this discussion because T1 nerve roots (Figure 7-1). It courses of space limitations but are compre- medial to the brachial artery throughout hensively reviewed by Stewart.4 the upper arm. In the distal arm, the

FIGURE 7-1 Median nerve. The nerve is labeled in bold, and sensory branches are labeled in italics.

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. KEY POINT nerve may pass beneath the ligament In the distal carpal tunnel, the h Patients with carpal of Struthers, which is present in some median nerve divides into the motor tunnel syndrome individuals (1% to 13%) and represents (thenar) branch and sensory branches classically present a rare cause of median nerve entrap- to the digits and palm. The motor with numbness, 5,6 ment. The nerve then passes under branch innervates the abductor tingling, and other the bicipital aponeurosis at the elbow. pollicis brevis, opponens pollicis, and paresthesia affecting Moving distally, the median nerve superficial head of flexor pollicis the first through third then travels between the two heads of brevis.10 An accessory thenar branch digits and the lateral the pronator teres, deep to the hu- may innervate the flexor pollicis brevis aspect of the fourth meral head and superficial to the ul- in nearly half of patients.10 digit. It is not unusual nar head. The nerve then continues Median nerve anatomic variants. for patients to report sensory symptoms distally between the flexor digitorum Martin-Gruber anastomoses are the affecting the entire superficialis and flexor digitorum most common anatomic variants af- hand or radiation from profundus muscles. Approximately fecting the median nerve, with an the hand to the proximal 4 cm distal to the medial epicondyle, estimated prevalence ranging from upper extremity. the anterior interosseus nerve branches 20% to 40%.11,12 Martin-Gruber anas- from the main trunk of the median tomoses typically leave the main me- nerve.5 The anterior interosseus nerve dian nerve or anterior interosseus innervates the flexor pollicis longus, nerve trunk near the elbow and cross flexor digitorum profundus to the over to join the ulnar nerve. There are second and third digits, and prona- four to six types of Martin-Gruber tor quadratus. anastomoses based on the exact anat- Just proximal to the distal wrist omy.12 The main significance of a crease, the palmar cutaneous branch of Martin-Gruber anastomosis is the the median nerve leaves the main nerve confounding effect that it may cause trunk.5 It travels between the palmaris in interpretation of electrodiagnostic longus and flexor carpi radialis tendons studies, as discussed later in this and proceeds outside the carpal tunnel article. Other rare anatomic variants to provide sensation for the thenar of the median nerve include the eminence and proximal lateral palm.7,8 Riche-Cannieu anastomosis (‘‘the all- The median nerve lies superficially ulnar hand’’), Berrettini anastomosis, at the volar distal wrist crease, an and Marinacci anastomosis (the reverse external landmark that roughly ap- Martin-Gruber anastomosis).11 proximates the carpal tunnel inlet. The flexor retinaculum forms the roof Clinical Presentation of the carpal tunnel. Deep to and The most common median mono- surrounding the nerve are the tendons neuropathy results from median nerve of the flexor pollicis longus, flexor compression at the wrist, causing digitorum superficialis, and flexor carpal tunnel syndrome. Patients with digitorum profundus.9 The hook of carpal tunnel syndrome classically the hamate, pyramidal, and pisiform present with numbness, tingling, and bones form the medial (ulnar) border other paresthesia affecting the first of the carpal tunnel, while the scaph- through third fingers and the lateral oid bone, trapezoid bone, and tendon aspect of the fourth finger. It is not of the flexor carpi radialis muscle unusual for patients to report sensory comprise the lateral (radial) aspect. symptoms affecting the entire hand or The floor or inferior margin of the radiation from the hand to the proxi- carpal tunnel formed by the carpal mal upper extremity. These sen- bones is known as the carpal sulcus. sory symptoms may be exacerbated

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by activities that require wrist flexion, weakened grip and difficulty per- including driving a car, and often wake forming fine motor tasks, and they the patient from sleep at night. Shaking may drop items easily. It is often or flicking the affected hand may allevi- unclear how much of the disability is ate the sensation, which can be quite related to loss of muscle strength as painful. Case 7-1 illustrates a classic opposed to loss of sensation. On case of early carpal tunnel syndrome. physical examination, careful observa- Weakness may occur in more ad- tion may reveal mild flattening of the vanced carpal tunnel syndrome. Pa- thenar eminence or frank atrophy. A tients describe a generalized sense of Tinel sign consists of paresthesia in

Case 7-1 A 24-year-old right-handed woman presented with numbness and tingling in her right hand that had begun about 3 months previously. Initially, the symptoms only occurred while carrying her infant son. She then began to wake at night with a sensation of painful numbness in the entire hand that radiated to her elbow. She tried wearing a neutral position wrist brace at night, but it provided only a minor degree of improvement. She had no history of wrist or upper limb injury. On examination, she had mild weakness of thumb abduction and loss of sensation over the entire palmar surface of the right first through third fingers and the lateral half of the fourth finger. Percussion over the midvolar wrist sent shooting electrical pains into her hand. Nerve conduction studies were performed and showed slowing of the median mixed and sensory nerve action potentials across the wrist with normal motor responses. Nerve ultrasound demonstrated enlargement of the median nerve at the carpal tunnel inlet (Figure 7-2). She was diagnosed with carpal tunnel syndrome and underwent a local corticosteroid injection performed by an orthopedic surgeon, resulting in relief of symptoms.

FIGURE 7-2 Ultrasonography showing the median nerve at the carpal tunnel inlet at the level of the distal wrist crease. A, Ultrasonography of the patient in Case 7-1 showing enlarged cross-sectional area (19 mm2) of the median nerve (arrow) associated with loss of nerve signal. B, Ultrasonography of a healthy control showing normal median nerve (arrow)measuring8mm2 at the distal wrist crease with normal signal.

Comment. This case is a classic presentation of carpal tunnel syndrome, confirmed by nerve conduction studies and nerve ultrasound. Although the median nerve sensory territory does not extend proximal to the wrist, patients often describe radiation of paresthesia into the arm, particularly upon waking. As an initial treatment option, nocturnal wrist splinting may relieve symptoms, although the response may be incomplete in more severe cases of carpal tunnel syndrome. In patients without axonal loss or weakness, corticosteroid injections of the carpal tunnel are a reasonable treatment option that may alleviate symptoms short of surgical decompression.

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. KEY POINTS the distal distribution of a sensory wrist and positive Phalen testing. h A negative Phalen test nerve when it is percussed. In carpal Depending upon the exact level of the is a strong predictor tunnel syndrome, a Tinel sign may be proximal median nerve lesion, weak- of normal nerve present at the distal wrist crease, but ness in the flexor pollicis longus, flexor conduction studies. the sensitivity may be as low as 30% digitorum profundus to the second h 13,14 Most neurologists to 43% with specificity up to 65%. and third digits, flexor digitorum consider electrodiagnostic The Phalen test is performed by superficialis, and pronator teres mus- testing to be the gold having the patient flex the wrists cles may be present. Isolated lesions standard in diagnosing and press the dorsum of both hands of the anterior interosseus nerve may carpal tunnel syndrome. together for 30 to 60 seconds. A false- lead to weakness in the flexor pollicis Considerable debate positive result may occur when longus, flexor digitorum profundus exists regarding the interpreting musculoskeletal wrist to the second and third digits, and the optimal set of tests for pain as a positive result, and spe- pronator quadratus. Unlike carpal making a diagnosis. cificity is only 15% to 17% range. tunnel syndrome, anterior interosseus Sensitivity of Phalen testing is better, neuropathies are generally due to but only around 50% to 67%.14Y16 noncompressive causes such as idio- Patients with positive Tinel and pathic brachial neuritis/neuralgic Phalen testing have lower nerve con- amyotrophy.19 duction velocities than those with negative testing.17 AnegativePhalen Electrodiagnostic Testing in test is a strong predictor of normal Carpal Tunnel Syndrome nerve conduction studies.18 Most neurologists consider electro- Strength testing for suspected car- diagnostic testing to be the gold pal tunnel syndrome should include standard in diagnosing carpal tunnel upper limb and especially forearm and syndrome. Considerable debate exists intrinsic hand muscles with special regarding the optimal set of tests for focus on the abductor pollicis brevis, making a diagnosis. The American opponens pollicis, and flexor pollicis Association of Electrodiagnostic Med- longus muscles. The finding of weak- icine, now known as the American ness in the abductor pollicis brevis Association of Neuromuscular and and opponens pollicis with normal Electrodiagnostic Medicine (AANEM), strength in the flexor pollicis longus has published basic guidelines for helps localize the pathology to the recommended electrodiagnostic test- carpal tunnel. More proximal lesions ing in patients with suspected carpal of the median nerve would involve the tunnel syndrome. The recommenda- flexor pollicis longus. Detailed sensory tions include performing an initial examination will reveal loss of sensa- median sensory nerve conduction tion in the palmar first through third study across the wrist at a distance digits and lateral fourth digit. Sensa- of 13 cm or 14 cm. If normal, a tion of the proximal lateral palm may shorter segment study (7 cm to be spared in carpal tunnel syndrome 8 cm) of the median mixed nerve is because of its innervation by the recommended. These studies should palmar cutaneous branch of the be performed with a radial or ulnar median nerve. sensory or mixed response across the More proximal lesions of the median same distance in the same limb for nerve have the same distribution of comparison of interlatency differ- sensory loss as seen in carpal tunnel ences. A median motor response syndrome with the addition of the recording over the abductor pollicis palm, but lack a Tinel sign at the brevis is also recommended, along

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KEY POINTS 22 h When performing with measurement of another motor evidence exists to support its use. nerve conduction response in the same limb. Optional In neuromuscular ultrasonography, studies, clinicians testing includes needle EMG of C5 to high-frequency ultrasound probes should be aware T1 muscles (to exclude cervical radi- provide detailed peripheral nerve of the changes caused culopathy as a contributing factor) anatomic information. Nerves are by a Martin-Gruber and supplementary nerve conduc- consistently enlarged at sites of com- anastomosis. tion studies.20 pression. In carpal tunnel syndrome, h Peripheral nerve Electrodiagnostic testing in Martin- the median nerve typically has a ultrasound is a useful Gruber anastomosis. When performing maximal point of enlargement at or tool in diagnosing median nerve conduction studies, cli- near the carpal tunnel inlet corre- entrapment neuropathies, nicians should be aware of the changes sponding to the surface anatomic with nerves consistently caused by a Martin-Gruber anastomo- marker of the distal wrist crease enlarged at or near sites sis. A Martin-Gruber anastomosis may (Figure 7-2). Reference values are of compression. result in low distal amplitude of the varied, but a cross-sectional area of median nerve compound muscle ac- the median nerve of greater than 12 mm2 tion potential (CMAP) when recording is generally considered abnormal. A over the abductor pollicis brevis and 2014 study found a cross-sectional stimulating at the wrist. With proximal area of greater than 10 mm2 to have nerve stimulation, the median CMAP 89% sensitivity and 90% specificity for amplitude will be higher. This can diagnosing carpal tunnel syndrome, create confusion and concern for as compared to a validated clinical overstimulation of the median nerve diagnostic tool.23 at the elbow, with costimulation of the Peripheral nerve ultrasound is a ulnar nerve. The presence of a Martin- useful tool in diagnosing entrapment Gruber anastomosis can be confirmed neuropathies, with nerves consistently by stimulating the median nerve at the enlarged at or near sites of compres- elbow and recording a CMAP in an sion. Substantial literature supports ulnar-innervated hand muscle, typically the use of ultrasound in diagnosing the first dorsal interosseus or abductor carpal tunnel syndrome.22,23 Neuro- digiti minimi.21 Identifying a Martin- muscular ultrasonography also pro- Gruber anastomosis by recording vides added value in understanding over ulnar-innervated thenar mus- the pathogenesis of carpal tunnel cles is discouraged, as the abductor syndrome. Routine ultrasound studies pollicis brevis CMAP may confound may reveal contributing factors or interpretation. A drop in amplitude issues that confound the diagnosis of between distal and proximal stimula- carpal tunnel syndrome. These may tion of the ulnar nerve may also be range from anatomic variants and present in a Martin-Gruber anasto- intraneural tumors to the relatively mosis and be mistaken for conduc- common bifid median nerve and the tion block.21 persistent median artery. The persistent median artery is an accessory Ultrasonographic Testing in artery that arises from the ulnar ar- Carpal Tunnel Syndrome tery in the proximal forearm as an Neuromuscular ultrasonography has embryologic remnant. When present, recently emerged as a novel diagnostic it courses with the median nerve tool for carpal tunnel syndrome. The through the forearm and carpal tun- exact role for neuromuscular ultra- nel. Other non-nerve findings may sonography in patient care is still include coexistent tenosynovitis or under investigation, but substantial accessory musculature.22

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. Electrodiagnostic and 26 KEY POINT treatment. These recommendations h The American Academy Ultrasonographic Testing in largely mirror those of the AAOS. of Orthopaedic Other Median Neuropathies The authors individualize treat- Surgeons states that Testing for proximal median neuropa- ment for carpal tunnel syndrome nonsurgical treatments thies involves the same techniques based on the severity of nerve com- (splinting and local used for the assessment of carpal pression as determined by the elec- corticosteroid injections) tunnel syndrome, with less need for fo- trodiagnostic findings. For patients are a reasonable cused testing across the carpal tunnel with mild carpal tunnel syndrome in- treatment option for and increased need for needle EMG to volving abnormal findings isolated to carpal tunnel syndrome help determine the level and severity of the median mixed or sensory re- for those early in the course of symptoms involvement. Neuromuscular ultraso- sponses, the authors begin a trial of without evidence neutral position wrist splinting and nography can be helpful in identifying of median nerve peripheral nerve trauma or other ab- nonsteroidal anti-inflammatory medica- denervation. A trial normalities of the nerve, including focal tions where appropriate. Patients who period of 2 to 7 weeks enlargement of proximal segments. do not experience satisfactory symp- is recommended to tom relief may subsequently be re- observe for improvement. Treatment of Carpal Tunnel ferred for a trial of local corticosteroid Syndrome injections. Decompressive surgery to Clinical practice guidelines are avail- transect the transverse carpal ligament able for the treatment of carpal tunnel may subsequently be considered in pa- syndrome, although adherence to tients with significant residual symp- these published standards varies widely toms. For patients with severe carpal in practice.24 The American Academy of tunnel syndrome with prolonged, low- Orthopaedic Surgeons (AAOS) states amplitude CMAPs and denervated that nonsurgical treatments (splinting median-innervated thenar muscles by of the wrist to a neutral position and needle EMG, the authors may employ local corticosteroid injections) are a the same treatments acutely but also reasonable option for those early in the refer patients for expeditious surgical course of symptoms without evidence consultation with a hand surgery spe- of median nerve denervation. A trial cialist in an effort to salvage the period of 2 to 7 weeks is recommended maximum degree of sensorimotor to observe for improvement. Carpal function in the hand. tunnel release is strongly recommended (Grade A, Level I evidence) either as a ULNAR NERVE first option for treatment or for those Ulnar neuropathy, often occurring at for whom nonsurgical therapies have or near the elbow, is the second most failed. The AAOS made no recommen- commonmononeuropathyseenin dations for patients with carpal tunnel outpatient neurology settings. syndrome and coexistent diabetes mellitus, cervical radiculopathy, or Basic Anatomy polyneuropathy or for carpal tunnel The ulnar nerve arises from the C8 to syndrome in the workplace.25 Heat T1 (and occasionally from C7 to T1) therapy, electrical stimulation, ionto- nerve roots and the medial cord of the phoresis, and laser therapies were brachial plexus and descends through among the treatments with no evi- the posteromedial arm, anterior to the dence to support their use.25 The medial head of the triceps brachii American Congress of Rehabilitative (Figure 7-3). The first branch off the Medicine (ACRM) also has published ulnar nerve is typically a sensory guidelines on carpal tunnel syndrome branch to the elbow, followed by a

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KEY POINT h The medial collateral ligament of the elbow defines the floor of the cubital tunnel, while the roof consists of the thickened fascia known as the Osborne (arcuate) ligament. This ligament lies between the medial and ulnar heads of the flexor carpi ulnaris.

FIGURE 7-3 Ulnar nerve. The nerve is labeled in bold, and sensory branches are labeled in italics. In the hand, the muscle labels abductor, opponens, and flexor apply to the abductor digiti minimi, opponens digiti minimi, and flexor digiti minimi.

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motor branch to the flexor carpi cubital tunnel is located just distal to ulnaris.27 Compression in the arm is the elbow. The medial collateral liga- rare but may occur at the arcade of ment of the elbow defines the floor of Struthers, a fibrous band running from the cubital tunnel, while the roof the medial head of the triceps to the consists of the thickened fascia medial intermuscular septum. Consid- known as the Osborne (arcuate) erable debate exists over the preva- ligament. This ligament lies between lence of this anatomic variant and its the medial and ulnar heads of the clinical significance.28 flexor carpi ulnaris. The ulnar nerve then passes through Within the proximal forearm, the the epicondylar (ulnar) groove, lo- ulnar nerve is located medial and cated between the medial epicondyle superior to the flexor digitorum pro- and the olecranon. An anomalous fundus and deep to the flexor carpi anconeus epitrochlearis muscle over- ulnaris and gives branches to inner- lying the ulnar nerve and extending vate these muscles along its course. between the olecranon and medial The ulnar nerve lies lateral to the epicondyle may be a source of com- flexor carpi ulnaris and medial to the pression in some individuals.27 The ulnar artery in the distal forearm.

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. KEY POINT Compression of the ulnar nerve in the clinical assessment should not reveal h The Guyon canal, or forearm is rare. an objective sensory deficit in the ulnar tunnel, is a site of The Guyon canal, or ulnar tunnel, is medial forearm. Patients may have potential ulnar nerve a site of potential ulnar nerve entrap- pain and tenderness near the epi- entrapment at the wrist. ment at the wrist. The canal extends condylar groove in cases of ulnar neu- The canal extends from from the proximal end of the pisiform ropathy at the elbow, although this the proximal end of the to the hook of the hamate. The flexor is not always present. pisiform to the hook of retinaculum and hypothenar muscles Ulnar motor dysfunction may be the hamate. define the floor, while the roof con- perceived as clumsiness with mild or sists of the volar carpal ligament. The early ulnar neuropathy at the elbow. lateral (radial) border is defined by the Patients may note difficulty with fine hook of the hamate, while the pisi- motor tasks or drop things easily. form, pisohamate ligament, and abduc- Frequently, patients experience weak- tor digiti minimi muscle belly compose ness of the fifth digit and may struggle the medial (ulnar) border. The ulnar to place it into a jacket or pants pocket nerve passes through the Guyon canal with the rest of the hand. Grip weak- with the ulnar artery.29 ness is also a frequent symptom with The Guyon canal can be further more advanced motor involvement. subdivided into zones. Zone 1 extends Observant patients may notice atrophy from the proximal volar carpal liga- of the intrinsic hand muscles, particu- ment to the bifurcation of the ulnar larly the first dorsal interosseous. nerve. Pathology in this region affects On clinical examination, the Froment both the motor and sensory functions sign may be present. To test for the of the nerve. Zone 2 extends laterally Froment sign, the patient is asked to beneath the palmaris brevis to the hold a thin object (eg, a sheet of paper) fibrous arch of the hypothenar mus- between the thumb and index finger cles and contains only motor fibers and an examiner attempts to remove it. of the ulnar nerve. Zone 3 extends In patients with weakness of the ulnar- medially from the ulnar nerve bifur- innervated adductor pollicis, the object cation and contains both motor and may be easily removed or the patient sensory fibers. The motor fibers form a may attempt to compensate for the superficial branch supplying the weakness by activating the median- palmaris brevis muscle, so zone 3 innervated flexor pollicis longus and pathology is generally considered to pinching with the distal phalanx of the affect only sensory function.30 thumb. Motor testing of the ulnar- innervated flexor digitorum profundus Clinical Presentation and to the fourth and fifth digits along with Examination Findings the flexor carpi ulnaris should be The ulnar nerve provides sensory performed as part of the standard innervation to the fourth and fifth examination. fingers, the medial palm, and the A Tinel sign may be present over dorsomedial hand. Patients with ulnar the ulnar nerve at sites of entrapment. neuropathy can present with pares- Gentle palpation of the epicondylar thesia that may range from a feeling of groove during elbow flexion and ex- deadness to shooting electriclike pains tension can be helpful in diagnosing that are most prominent in the fourth ulnar nerve subluxation, which is also and fifth digits. It is not unusual for present in a proportion of asymp- patients to note pain radiation be- tomatic individuals.31 Although its tween the elbow and hand, although presence is not diagnostic of ulnar

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KEY POINT h Needle EMG is essential neuropathy and it is not an established minimumof10cmshouldbepresent in assessing ulnar risk factor, identifying subluxation may between the above-elbow and below- neuropathy at be helpful in selecting the appropriate elbow sites of stimulation. The diag- the elbow. surgical intervention in patients with nosis of ulnar neuropathy at the elbow ulnar neuropathy at the elbow. Sublux- can be made when the conduction ation can be detected by palpation of velocity across the elbow is greater than theulnarnervemovingoverthe or equal to 10 m/s slower than the wrist medial epicondyle with flexion or ex- to below-elbow segment. Other sup- tension at the elbow. portive findings include a drop in CMAP Although rarely used by neurolo- amplitude of greater than 20% across gists, the surgical literature makes the elbow.33 frequent use of the McGowan grading Criticism of the initial AANEM guide- system in the assessment of ulnar lines center on their lack of sensi- neuropathy at the elbow. It is helpful tivity for precise localization in some to know this system when reviewing patients with ulnar neuropathy at the the literature on the topic and com- elbow. Sensitivity has ranged from municating with surgical colleagues. 37% to 86%, while specificity has been Grade 1 consists of paresthesia in the greater than 95%.34 Techniques for fourth and fifth digits and a feeling of improving sensitivity reduce specific- hand clumsiness. Grade 2 includes ity, and this should be considered weakness and impaired sensation, when performing additional testing. sometimes with mild atrophy of the Inching is a popular technique often intrinsic hand muscles. In McGowan used to identify sites of pathology in grade 3, the sensory and motor defi- ulnar neuropathy at the elbow. The cits are severe and marked muscle 10-cm segment between the above- atrophy is present.32 elbow and below-elbow sites is di- vided into 2-cm segments. Stimulation Electrodiagnostic Testing is applied at each point, with attention Electrodiagnostic testing is considered to the latency differences and CMAP the gold standard for the diagnosis of waveforms. Using this approach, the ulnar neuropathy, but the recom- sensitivity of nerve conduction studies mended testing and definition of is improved, detecting up to 90% of abnormality is debated. The majority patients with clinical evidence of ulnar of work published has centered on neuropathy at the elbow.35 Although ulnar neuropathy at the elbow, the this technique offers improved sensi- most common variant of ulnar neu- tivity and more precise localization, it ropathy. AANEM guidelines are fre- requires attention to technical detail quently cited in most studies of ulnar for accurate results. neuropathy at the elbow.33 The Needle EMG is essential in as- AANEM guidelines for the diagnosis sessing ulnar neuropathy at the elbow, of ulnar neuropathy at the elbow as outlined in Case 7-2. Examination recommend performing ulnar sensory of ulnar-innervated muscles is helpful nerve conduction studies and motor for both localization and assessment nerve conduction studies to the ab- of severity. Other muscles with C7 and ductor digiti minimi. Elbow position C8 innervation should also be sampled during testing (with flexion between to assess for the presence of coexis- 70 degrees and 90 degrees recom- tent cervical radiculopathy or bra- mended) should be recorded and chial plexopathy. Electromyographers adequate warming maintained. A should be aware that little evidence

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. KEY POINT Case 7-2 h As with carpal tunnel syndrome, neuromuscular A 52-year-old left-handed man noted progressive numbness and tingling ultrasonography has of his right fourth and fifth fingers. His hand was clumsy at times, and he emerged as an began having difficulty buttoning his shirts. He reported a ‘‘funny bone’’ alternative means of sensation that radiated into his right hand, particularly after talking on the assessing ulnar phone for extended periods of time. Examination demonstrated mild neuropathy at the elbow. atrophy of the right first dorsal interosseus muscle. A Tinel sign was The normal ulnar nerve present over the right epicondylar (ulnar) groove. He had moderate cross-sectional area is weakness of right finger abduction and deep finger flexion of the fourth 8mm2 to 11 mm2 and fifth digits with minimal weakness of thenar and finger extensor at the elbow, with muscles. He also had sensory loss over the right medial palm, the medial larger values suggesting aspect of the fourth finger and the entire fifth finger, and the dorsal focal compression. medial hand. Ulnar neuropathy at the elbow was suspected and classified as a McGowan grade 2 based upon the clinical assessment. The patient’s physician chose not to perform electrodiagnostic testing at that time. An evaluating surgeon recommended ulnar nerve transposition, as weakness and atrophy were already present. Following surgery, the patient continued to have progressive symptoms and was then referred for electrodiagnostic studies. Testing performed 6 months after surgery revealed mild slowing of the ulnar motor conduction velocity at the elbow with normal sensory responses. Ultrasonography of the ulnar nerve was normal. Detailed needle EMG found evidence of denervation and reinnervation in the right extensor indicis proprius, first dorsal interosseus, abductor pollicis brevis, and C8 to T1 paraspinals. Along with a mild right ulnar neuropathy at the elbow, a coexistent right C8 radiculopathy was diagnosed and confirmed by imaging of the cervical spine. Comment. Although the patient had symptoms compatible with ulnar neuropathy at the elbow, mild weakness of thenar (median) and finger extensor (radial) muscles was overlooked, and he was referred for surgical intervention before the localizations for the deficits were confirmed. When he failed to improve, electrodiagnostic studies subsequently performed showed that a C8 radiculopathy was also present. This is an example of double crush syndrome, in which two separate peripheral nerve lesions occur along the course of the same nerve with both lesions contributing to the clinical findings. This case illustrates the importance of careful clinical examination and electrodiagnostic testing to establish accurate localization prior to surgery. exists regarding the utility of needle ultrasonography is not believed to be EMG in determining prognosis.36 a superior means of diagnosing ulnar neuropathy at the elbow for all pa- Ultrasonographic Testing tients, although limited evidence in- As with carpal tunnel syndrome, neu- dicates that it may be more sensitive romuscular ultrasonography has than nerve conduction studies early in emerged as an alternative means of the disease.38,39 Neuromuscular ultra- assessing ulnar neuropathy at the sonography is best used as an adjunct elbow. The normal ulnar nerve cross- to clinical and electrodiagnostic data sectional area is 8 mm2 to 11 mm2 at to aid in localization.40 It is helpful the elbow, with larger values suggesting in pinpointing the area of pathology focal compression.37 Neuromuscular and may identify alternative etiologies

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KEY POINTS h for ulnar neuropathy at the elbow. outcomes with anterior ulnar nerve Testing of the dorsal 43 ulnar cutaneous sensory These include anatomic variants (eg, transposition. Other studies have nerve response can be anomalous anconeus epitrochlearis favored simple decompression over added to EMG and muscle), ganglion cysts, and other transposition, unless difficulties with ultrasonography when mass lesions. painful ulnar nerve luxation over the assessing lesions distal The evaluation of ulnar neuropathy medial epicondyle are present.43 to the elbow, assisting outside the elbow region follows No consensus exists on when ulnar in localization of an many of the previously mentioned neuropathy at the elbow becomes ulnar neuropathy at or principles. Whether evaluating proxi- severe enough to warrant surgery. proximal to the wrist. mal or distal lesions, ulnar motor and Some have suggested that surgical h Three months of sensory nerve conduction studies are treatment is warranted in patients with conservative treatment essential. Ultrasonography and needle mild (McGowan grade 1) ulnar neu- with the use of elbow EMG also provide helpful additive in- ropathy at the elbow. Excellent out- pads and avoidance of formation. Testing of the dorsal ulnar comes have been reported in this prolonged elbow flexion cutaneous sensory nerve response can population using simple decompres- is recommended as be added when assessing lesions distal sion and medial epicondylectomy.44 first-line treatment in those patients with to the elbow, assisting in localization Further supporting the case for early ulnar neuropathy at the of ulnar nerve lesions at or proximal to intervention are data demonstrating elbow with mild the wrist. The dorsal ulnar cutaneous that patients with McGowan grade 3 symptoms and less sensory nerve response will be normal ulnar neuropathy at the elbow are severe electrodiagnostic with the lesions at the wrist, but more likely to have fair or poor findings. Up to 50% of abnormal with lesions in the region postsurgical outcomes.45 patients will have of the proximal forearm or elbow. Few alternative approaches to the resolution of symptoms treatment of ulnar neuropathy at the with this approach. Treatment of Ulnar Neuropathy elbow are available. Unlike in carpal h Unlike in carpal at the Elbow tunnel syndrome, corticosteroid injec- tunnel syndrome, The best approach to treating ulnar tions have not shown efficacy in ulnar corticosteroid injections neuropathy at the elbow remains con- neuropathy at the elbow.46,47 Ultra- have not shown efficacy troversial. Three months of conserva- sound and low-level laser therapy have in ulnar neuropathy at tive treatment with the use of elbow shown some promise but are neither the elbow. pads and avoidance of prolonged elbow widely accepted nor available.48 Addi- flexion is recommended as first-line tional research is needed to under- treatment in those with mild symptoms stand how clinical, electrodiagnostic, and less severe electrodiagnostic find- and sonographic data might be com- ings. Up to 50% of patients will have bined to predict and optimize pa- resolution of symptoms with this ap- tient outcomes in ulnar neuropathy proach.41 For patients for whom con- at the elbow. servative measures fail or who have evidence of significant axonal loss on RADIAL NERVE initial electrodiagnostic examination, The radial nerve is less likely to be surgical management is indicated. affected by chronic compression than Three general approaches are used: the median or ulnar nerves but re- simple decompression through exci- mains a frequent mononeuropathy sion of the arcuate ligament, medial because of acute compressive lesions. epicondylectomy, and ulnar nerve transposition.42 An early analysis of Basic Anatomy published data demonstrated that The radial nerve is the terminal branch patients with more severe disease of the posterior cord of the brachial (McGowan grade 3) have the best plexus (Figure 7-4). In the axilla, the

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B 2016 Vern C. Juel. radial nerve yields three branches, the lateral epicondyle, with branches including the posterior brachial cuta- to the brachioradialis and the exten- neous nerve and branches innervating sor carpi radialis longus and brevis. the long and medial heads of the The nerve then bifurcates into two triceps brachii. It then travels with terminal branches, a superficial sen- the deep brachial artery between sory branch and a deep branch called the long head of the triceps and the the posterior interosseous nerve. humerus and courses through the The posterior interosseous nerve spiral groove between the lateral passes through the arcade of FrPhse, and medial heads of the triceps. Two formed by a fibrous arch arising from sensory branches are present in this the superficial head of the supina- region, including the lower lateral tor muscle at its attachment to the brachial cutaneous nerve, the poste- lateral epicondyle. The posterior inte- rior antebrachial cutaneous nerve, and rosseous nerve travels between and motor branches to the lateral and innervates the superficial and deep medial heads of the triceps. After heads of the supinator muscle to passing through the lateral inter- supply the wrist and finger extensor muscular septa, the radial nerve muscles.49 The superficial sensory travels between the brachialis and bra- branch supplies sensation to the dor- chioradialis muscles just anterior to solateral hand. It lies beneath the

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KEY POINTS h Slowly progressive radial brachioradialis muscle at the elbow Posterior interosseous syndrome is neuropathy may occur and in the proximal forearm as it a pure motor syndrome without asso- with humeral fracture travels with the radial artery. In the ciated sensory loss. It is much less healing due to callus distal third of the forearm, the nerve commonthanradialcompression formation creating separates from the artery and travels at the spiral groove and results from nerve entrapment. superficially beneath the brachio- posterior interosseous nerve com- h Posterior interosseous radialis tendon. The nerve then pression within the arcade of Fro¨hse syndrome is a pure travels between the brachioradialis related to repetitive supination, space- motor syndrome and extensor carpi radialis longus occupying lesions, and trauma. It pre- without associated tendons. Distally, the nerve pierces sents with marked weakness of finger sensory loss. the overlying forearm fascia and di- extension and a lesser degree of wrist h Electrodiagnostic vides into lateral and medial divi- extension weakness. Wrist extension testing of the radial sions and ultimately into dorsal digital may be relatively spared due to exten- nerve requires nerve nerves.50 sor carpi radialis longus innervation conduction studies and occurring proximal to the division of needle EMG. Clinical Presentation and the common radial nerve (Figure 7-4). Examination Findings As the posterior interosseous nerve is a The most common presentation of purely motor nerve, patients experi- radial neuropathy is that of acute ence no sensory symptoms. Patients compression at the level of the spiral sometimes report vague discomfort groove, commonly known as Saturday over the dorsal forearm, worsened by night palsy. In this syndrome, pa- activity involving supination of the arm. tients compress the medial arm Pain with resisted supination of the against a firm surface (eg, arm draped forearm can be used as a provocative over a chair back) during prolonged test, but its specificity and sensitivity sleep, deep sedation, or intoxica- are poorly defined. tion. They may awaken unable to Isolated lesions of the superficial extend the fingers or wrist. Numbness radial sensory nerve may also occur. or paresthesia is present over the These may result from focal com- dorsolateral hand. Pain at the spiral pression or trauma, as in cheiralgia groove is relatively uncommon. The paresthetica (compression of the su- symptoms typically resolve over 2 to perficial radial nerve at the wrist), or 3 months. as a rare type of diabetic mono- Because of the close association neuropathy.56Y58 Patients experience between the radial nerve and the sensory loss, sometimes associated humerus, fractures of the humeral with uncomfortable paresthesia over shaft are also a common cause of the dorsolateral hand. Sensory test- proximal radial neuropathies.51,52 ing of the affected region and the Examination findings are dependent absence of associated weakness are upon the level of the fracture. Acute essential in making the clinical diagnosis. presentations are readily identified in most cases, but delayed involvement Electrodiagnostic Testing may be overlooked. Slowly progres- Electrodiagnostic testing of the radial sive radial neuropathy may occur nerve requires nerve conduction stud- with fracture healing due to callus ies and needle EMG. Typically, the formation creating nerve entrap- radial motor response is recorded ment53 or may be related to the over the extensor indicis proprius surgical hardware used to repair the following stimulation at the forearm, fracture itself.54,55 lateral elbow, and spiral groove. This

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. KEY POINTS permits assessment of potential areas gation is needed to determine how h Needle EMG can assist of entrapment, and special attention finding these secondary lesions might in localization and to CMAP amplitudes and dispersion is impact prognosis and treatment. Al- prognosis of radial nerve necessary. Stimulation at Erb point is though peripheral nerve trauma is not entrapment. The triceps helpful in localizing proximal humeral covered in this article, neuromuscular brachii, brachioradialis, lesions, although costimulation of the ultrasonography can be used to deter- and long head of brachial plexus may contaminate the mine nerve continuity within hours or extensor carpi radialis recordings.59 A superficial radial sen- days of peripheral nerve trauma, expe- are spared with isolated sory response is valuable for differen- diting treatment decisions. posterior interosseous tiating between common radial and nerve pathology. posterior interosseous nerve pathol- Treatment of Radial h The most common of ogy. As with any mononeuropathy, Neuropathies the radial neuropathies, nerve conduction studies of other The most common of the radial neu- acute compression at upper extremity nerves may be needed ropathies, acute compression at the the spiral groove to confirm isolated involvement of the spiral groove (Saturday night palsy), (Saturday night palsy), typically resolves radial nerve. typically resolves without additional without additional Needle EMG can assist in localization intervention. These acute compres- intervention. These and prognosis. The triceps brachii, sions cause focal demyelination that acute compressions brachioradialis, and long head of ex- will resolve within 2 to 3 months. cause focal demyelination tensor carpi radialis are spared with Avoidance of further compression is that will resolve within isolated posterior interosseous nerve recommended during this time. If 2to3months. pathology. Distally, the extensor secondary axonal damage has oc- digitorum communis and extensor curred, recovery may take longer and indicis proprius muscles are sampled. be incomplete. Additional examination of nonradial Aside from repair of traumatic muscles is helpful and often neces- nerve injuries and compression sary in excluding brachial plexopathy due to mass lesions, surgical inter- or cervical radiculopathy as a cause ventions for radial neuropathy are of symptoms. uncommon, and no standard pro- cedures exist for routine release of Ultrasonographic Testing the radial nerve. Neuromuscular ultrasonography may In patients with posterior interos- also be used in the diagnosis of radial seous syndrome, anti-inflammatory neuropathies. Focal enlargement has medications, rest, and corticosteroid been documented at sites of compres- injections are common first-line treat- sion and can be helpful in localization. ment recommendations.63 Surgical re- Radial nerve cross-sectional area is lease of the superficial head of the typically less than 10 mm2 in the supinator muscle may be performed upper arm and antecubital fossa, with in patients for whom conservative the superficial radial sensory nerve management has failed, but this is measuring only 1 mm2 to 3 mm2.60,61 rarely performed at the authors’ insti- The posterior interosseous nerve tution. Although the surgical literature cross-sectional area measures ap- reports good response to treatment proximately 2 mm2.62 Interestingly, in most cases,65,66 patients involved distal enlargement of the posterior in workers’ compensation claims are interosseous nerve has been docu- known to have less favorable out- mented in cases of proximal radial comes.67 Given the lack of large nerve lesions, suggesting a double prospective trials and potential for crush syndrome.63,64 Additional investi- surgical complications,68 posterior

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KEY POINT h The common fibular interosseous nerve release surgery is the short head of the biceps femoris (peroneal) nerve is the not routinely advised. muscle before separating from the lateral division of the sciatic nerve in the popliteal fossa. sciatic nerve and FIBULAR (PERONEAL) NERVE The nerve branches within the fossa formed by the L4 to Fibular neuropathy is the most fre- to make a small contribution to the S1 spinal roots. quent entrapment neuropathy of the sural nerve, although considerable var- lower extremity. An organized diag- iability exists. The fibular tunnel, a nostic approach is necessary in the potential site of nerve entrapment, is evaluation of affected patients. composed of the arch made by the peroneus longus, the soleus tendon, Basic Anatomy and the proximal fibula.69 The common fibular (peroneal) nerve is At the level of the fibular head, the the lateral division of the sciatic nerve common fibular nerve divides into deep and formed by the L4 to S1 spinal roots. and superficial divisions (Figure 7-5 It branches from the sciatic nerve in the and Figure 7-6). The deep branch of distal thigh and wraps around the the fibular nerve provides innervation biceps femoris tendon and fibular head to the muscles of the anterior com- on its course to the anterolateral leg.69 partment (tibialis anterior, extensor The fibular nerve gives off a branch to digitorum longus, extensor hallucis

FIGURE 7-5 Common and deep fibular (peroneal) nerves. The nerves are labeled in bold, and sensory branches are labeled in italics.

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. KEY POINT h Compression of the common fibular nerve at the level of the fibular head is the most common lower extremity mononeuropathy. Common causes include weight loss, prolonged immobility, and frequent crossing of the legs.

FIGURE 7-6 Common and superficial fibular (peroneal) nerves. The nerves are labeled in bold, and sensory branches are labeled in italics.

B 2016 Vern C. Juel. longus, peroneus tertius, extensor lar neck exostosis, and acute compres- digitorum brevis) and sensation to the sion after wearing tight-fitting pants dorsal web space between the first and (ie, skinny jeans).72Y74 Patients with second toes. The superficial fibular common fibular neuropathy typically nerve innervates the lateral compart- present with difficulty walking. While ment muscles (peroneus longus and some patients describe overt footdrop, peroneus brevis) and supplies sensa- many will report a ‘‘toe dragging,’’ tion to the distal lateral leg and dor- ‘‘foot slapping,’’ or frequent tripping. sal foot.70 Paresthesia is sometimes noted in the lower lateral leg and dorsal foot but is Clinical Presentation and often overlooked in the setting of Examination Findings significant weakness. Pain may also be Compression of the common fibular present at the site of compression. nerve at the level of the fibular head is Detailed physical examination may the most common lower extremity reveal a Tinel sign over the fibular nerve mononeuropathy.71 Common causes near the knee. Observation may dem- include weight loss, prolonged immo- onstrate frank footdrop when walking bility, and frequent crossing of the legs. or steppage gait. In milder cases, the Other etiologies include prolonged gait may appear unaffected, with weak- squatting, knee dislocation, ankle ness noted only when the patient is sprains, intraneural ganglion cysts, fibu- asked to walk on his or her heels. Motor

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KEY POINTS h Any weakness of ankle testing will reveal weakness in the ankle Other L4 to L5 and sciatic muscles inversion, toe flexion, or dorsiflexor, evertor, and toe extensor should be sampled to differentiate hip abduction suggests muscles. Sensory loss can be variable isolated fibular mononeuropathy from an L5 radiculopathy as but typically spares the dorsal fifth toe. sciatic neuropathy, lumbosacral plexo- opposed to an isolated Any weakness of ankle inversion, toe pathy, and lumbar radiculopathy. For fibular neuropathy. flexion, or hip abduction suggests an example, abnormalities on needle h Superficial fibular L5 radiculopathy as opposed to an EMG of the tibialis posterior can assist neuropathies spare isolated fibular neuropathy. in differentiating L5 radiculopathy sensation in the first Cases of isolated deep fibular neuro- from fibular neuropathy. dorsal web space, pathy are less common. Etiologies as the deep fibular include trauma, compression, and Ultrasonographic Testing nerve innervates this ganglion cysts.75 Involvement spares On neuromuscular ultrasonography, sensory field. the ankle evertors and sensation of increased cross-sectional area is pres- the lateral leg and foot. Sensory loss ent at sites of compression; early of the web space between the first and studies suggest that larger nerve second toes is present. Superficial cross-sectional area is associated with fibular neuropathy is also relatively axonal loss.76 The nerve is usually rare. Depending upon the level of smaller than 12 mm2 at the level of involvement, it can present with sen- the fibular head.60 Neuromuscular sorimotor or isolated sensory symp- ultrasonography in fibular neuropathy toms. Weakness of ankle eversion is at the fibular head may reveal ana- detected in more proximal disease, tomic causes, particularly in patients while loss of sensation over the lateral without risk factors for nerve com- leg and dorsolateral foot can occur pression. In one study, neuromuscular with either proximal or distal lesions. ultrasonography demonstrated com- The web space between the first and pressive intraneural ganglion cysts at second toes will be spared any loss of the fibular head in 18% of patients.72 sensation, as the deep fibular nerve A 2015 analysis found abnormal bi- supplies this area. ceps femoris anatomy, ganglion cysts, and lipomas in a series of only 21 Electrodiagnostic Testing patients with footdrop due to com- Motor nerve conduction studies of mon fibular neuropathy.77 This type of the fibular nerve are performed with information cannot be obtained from the recording electrode placed over the electrodiagnostic testing alone and is extensor digitorum brevis with stimu- essential in guiding appropriate treat- lation at the anterior ankle, fibular ment. Case 7-3 describes how electro- head, and popliteal fossa. If the motor diagnostic studies and neuromuscular response is absent, the recording ultrasonography can be used together electrode can be placed over the in clarifying complicated cases of tibialis anterior with stimulation at fibular nerve entrapment. the fibular head and popliteal fossa. The superficial fibular sensory re- Fibular Neuropathy Treatment sponse can also be performed to assist Treatment of fibular neuropathy is in localization. guided by etiology. Surgical repair is Needle EMG is necessary to assess often necessary after traumatic injury. severity and assist in prognosis. A Compressive intraneural ganglion minimum examination consists of the cysts must be excised to prevent re- tibialis anterior, peroneus longus, and currence and further nerve injury. For short head of the biceps femoris. unremarkable cases of compression

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. Case 7-3 A 79-year-old man with lung cancer noted left foot weakness after entering a rehabilitation program following a 2-month hospital stay. He was persistently tripping over his left foot, and his wife stated that his walking was ‘‘too loud.’’ He denied any trauma to the leg and had not noticed any pain but did describe an intermittent tingling sensation over his dorsal left foot. He had no low back pain. Examination was remarkable for cachexia and mild diffuse weakness of the bilateral upper and lower extremities. He also had superimposed weakness with only movement against gravity for left ankle dorsiflexion, ankle eversion, and extension of all toes. Bilateral lower extremity reflexes were absent, and he had reduced sensation in a stocking-glove distribution bilaterally. Electrodiagnostic testing demonstrated evidence of a widespread sensorimotor axonal polyneuropathy. No fibular motor response was present with recording over the extensor digitorum brevis on either side. Bilateral superficial fibular sensory responses were absent bilaterally, as were sural sensory responses. Needle EMG exhibited denervation and reinnervation in the bilateral tibialis anterior and medial gastrocnemius, but the changes were most prominent in the left tibialis anterior. A fibular motor response recording over the left tibialis anterior demonstrated a drop in amplitude and slowing across the fibular head. Ultrasound of the left fibular nerve at this site showed marked focal enlargement of the nerve. The patient was diagnosed with left fibular neuropathy at the fibular head superimposed on a background of sensorimotor polyneuropathy. Comment. The patient in this case had a preexisting polyneuropathy complicating assessment of superimposed mononeuropathies. Fibular neuropathy at the fibular head was strongly suspected given the patient’s presentation and risk factors of immobilization and apparent weight loss. The use of needle EMG, alternate recording sites for fibular motor responses, and ultrasonography permitted an accurate diagnosis. at the fibular head with no or minor OTHER LOWER EXTREMITY changes on electrodiagnostic testing, ENTRAPMENT NEUROPATHIES time and avoidance or correction of Any peripheral nerve can be affected risk factors may suffice. For more by entrapment. A few of the lesser severe cases involving axonal loss, sur- known peripheral nerve entrapment geryisindicated.Thisiscompli- syndromes are reviewed here. cated by lack of a standard approach and the existence of differing sites of Tarsal Tunnel Syndrome potential entrapment. Most patients The tibial nerve derives from the sciatic have improvement in function and nerve and receives contributions from pain following intervention, but the the L4 to S1 nerve roots. The tibial published studies are small and nerve branches from the sciatic nerve at lack standardization.78Y80 Microsurgical the level of the popliteal fossa and decompression, with dissection of only travels distally beneath the arch of the the fibrous band between the superfi- soleus. Its branches provide innervation cial head of the peroneus longus and to muscles of ankle plantar flexion and the soleus, may be an equally effective to the sural nerve. At the level of the approach as compared to a more ankle, it passes through the tarsal invasive surgical decompression.81 tunnel before dividing into its terminal

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KEY POINTS 89 h The tarsal tunnel branches, the medial and lateral plan- diagnosis. Neuromuscular ultraso- represents the space tar nerves. The tarsal tunnel repre- nography may aid in assessment of between the flexor sents the space between the flexor structural causes of tarsal tunnel syn- 90 retinaculum and medial retinaculum and medial malleolus, drome symptoms, and some reports malleolus, containing containing the tibial nerve, posterior establish cross-sectional area cutoff the tibial nerve, tibial artery, posterior tibial vein, flexor values to be used in the diagnosis of posterior tibial artery, hallucis longus, tibialis posterior, and idiopathic tarsal tunnel syndrome. posterior tibial vein, flexor digitorum longus.82 The medial In the absence of a structural cause flexor hallucis longus, and lateral plantar nerves supply of compression, the exact value of tibialis posterior, and cutaneous sensation over the plantar surgical decompression is unknown. flexor digitorum longus. surface of the foot, along with inner- A 2015 review of 31 patients undergo- h Idiopathic tarsal tunnel vation of intrinsic foot muscles. The ing surgery for tarsal tunnel syndrome syndrome is rare. tarsal tunnel is a potential site of tibial demonstrated good outcomes in 71% Potential etiologies of nerve entrapment. but found that only 6 of 11 patients tibial neuropathy at the Tarsal tunnel syndrome, also known with idiopathic tarsal tunnel syndrome ankle include trauma, as tibial neuropathy at the ankle, is a improved. The best surgical outcomes masses, accessory muscles, bony controversial topic in neurology. In occurred in those with a determined malformations, vascular most cases, the diagnosis is established cause of tarsal tunnel syndrome, in- 91 anomalies, and by clinical presentation, although diag- cluding trauma and masses. This iatrogenic causes. nostic criteria are ill defined. Symp- should be considered when designing h The most common toms consist of numbness and painful a treatment plan. location for Morton paresthesia involving the heel, medial neuroma is the ankle, and the sole of the foot, al- Morton Neuroma third or fourth though some definitions include ankle Although a separate entity from tarsal 82 interdigital nerves. pain with weight bearing. A Tinel tunnel syndrome, Morton neuroma is sign may be present over the tibial a distal tibial mononeuropathy pre- nerve at the ankle. In the authors’ expe- senting with shooting pains into the rience, idiopathic tarsal tunnel syn- toes and other associated paresthesia drome is rare. Potential etiologies of of the forefoot provoked by weight tibial neuropathy at the ankle include bearing. It results from chronic repet- trauma, masses,83 accessory mus- itive mechanical trauma of a plantar cles,84,85 bony malformations,86 vascu- digital nerve and is considered to lar anomalies,87 and iatrogenic causes.88 represent a degenerative perineural Electrodiagnostic testing can be fibrous enlargement of the nerve, as helpful in excluding other causes of opposed to a true neuroma. The most tarsal tunnel syndrome symptoms, but common location is the third or fourth itsexactutilityindiagnosisisun- interdigital nerves. Diagnosis is through known.89 No single set of characteristic clinical examination and, more recently, electrodiagnostic findings exists, as it is ultrasound imaging.92Y94 often stated that plantar nerve responses are frequently unobtainable Meralgia Paresthetica in individuals who are asymptomatic, Meralgia paresthetica is the commonly particularly with advanced age. A sys- used term describing pathology of the tematic review of the literature from lateral femoral cutaneous nerve, also 1965 to 2002 yielded only four studies known as the lateral cutaneous nerve meeting review criteria, and these of the thigh. The lateral femoral met only Class III level of evidence. cutaneous nerve arises from the L1 The review concluded that nerve con- to L3 nerve roots and lumbar plexus duction studies might be helpful in and is a pure sensory nerve. Its path

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Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited. KEY POINT over the iliacus and under the ingui- gies and require special investigation. h Treatment of meralgia nalligamentmakeitpronetoinjury Entrapment neuropathies may present paresthetica is most 95 and compression. The lateral fem- in the context of other peripheral often conservative, oral cutaneous nerve may have a neuropathic processes and be super- including behavioral variable course between individuals, imposed on a background of poly- modifications (eg, with five distinct patterns identified, neuropathy or occur in parallel with wearing looser clothing), making diagnostic testing and treat- other mononeuropathies or radicu- symptomatic relief of ment challenging.96 lopathies. Clinical assessment and local- painful paresthesia Meralgia paresthetica is associated ization may be confirmed and refined with nonsteroidal with obesity, diabetes mellitus, and with electrodiagnostic studies and neu- anti-inflammatory drugs, wearing tight clothing.95 Other causes romuscular ultrasonography. Electro- and nerve blocks. include trauma and surgical injury. Typ- diagnostic studies provide physiologic ical symptoms of meralgia paresthetica information regarding peripheral nerve include lateral or anterolateral thigh and muscle function, and neuromus- paresthesia and sensory loss. Pain can cular ultrasonography provides com- be severe and described as stabbing, plementary anatomic information. shooting, or burning. Physical exami- Early diagnosis and expeditious treat- nation should reveal sensory loss in ment seek to minimize morbidity and the distribution of the lateral femoral maximize function to achieve optimal cutaneous nerve without associated patient outcomes. findings suggestive of lumbar radiculopathy or lumbosacral plexopathy. REFERENCES Electrodiagnostic testing is useful not 1. Musolin K, Ramsey JG, Wassell JT, Hard DL. only in diagnosis but also for exclu- Prevalence of carpal tunnel syndrome sion of other causes. Neuromuscular among employees at a poultry processing ultrasonography can be helpful in plant. Appl Ergon 2014;45(6):1377Y1383. doi:10.1016/j.apergo.2014.03.005. guiding electrode placement for testing the lateral femoral cutaneous nerve 2. Latinovic R, Gulliford MC, Hughes RA. Incidence of common compressive and for identifying areas of focal neuropathies in primary care. J Neurol nerve enlargement.97,98 Neurosurg Psychiatry 2006;77(2):263Y265. Treatment of meralgia paresthetica doi:10.1136/jnnp.2005.066696. is most often conservative, including 3. Ono S, Clapham PJ, Chung KC. Optimal behavioral modifications (eg, wearing management of carpal tunnel syndrome. Int J Gen Med 2010;3:255Y261. doi:10.2147/ looser clothing), symptomatic relief of IJGM.S7682. painful paresthesia with nonsteroidal 4. Stewart J. Pathologic processes producing anti-inflammatory drugs, and nerve focal peripheral neuropathies. Focal blocks.95 Surgical exploration and peripheral neuropathies. 4th ed. West treatment should be considered a last Vancouver, Canada: JBJ Publishing, 2010. resort in the absence of a mass lesion. 5. Dang AC, Rodner CM. Unusual compression neuropathies of the forearm, part II: median nerve. J Hand Surg Am 2009;34(10): CONCLUSION 1915Y1920. doi:10.1016/j.jhsa.2009.10.017. Entrapment neuropathies are a com- 6. Siqueira MG, Martins RS. The controversial mon indication for outpatient neuro- arcade of Struthers. Surg Neurol logic consultation. While some are 2005;64(suppl 1):S1:17Y20; discussion Y quite common and easily diagnosed, S11:20 21. doi:10.1016/j.surneu.2005.04.017. such as carpal tunnel syndrome and 7. Bezerra AJ, Carvalho VC, Nucci A. An anatomical study of the palmar cutaneous ulnar neuropathy at the elbow, others branch of the median nerve. Surg Radiol Anat may result from more obscure etiolo- 1986;8(3):183Y188. doi:10.1007/BF02427847.

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