Chapter 24Chapter 24

Focal Peripheral Focal Peripheral NeuropathiesNeuropathies

Alireza Ashraf, M.D.Professor of Physical Medicine & Rehabilitation

Shiraz Medical school

EntrapmentEntrapment within a compartment of within a compartment of relatively fixed size, compression by relatively fixed size, compression by an internal or external source, an internal or external source, repetitive trauma andrepetitive trauma and

overuse, or some other etiology overuse, or some other etiology affecting a nerve over a finite affecting a nerve over a finite segment is one of the most common segment is one of the most common lesions evaluated by anlesions evaluated by an

electrodiagnostic medicine consultant.electrodiagnostic medicine consultant.

AXONAL LOSSAXONAL LOSS

SNAPSNAP for approximately 9-10 days for approximately 9-10 days compound muscle action potential compound muscle action potential

(CMAP) disappears by day 7-8 because (CMAP) disappears by day 7-8 because of neuromuscular junction of neuromuscular junction transmission failuretransmission failure

SNAPSNAP

Preserved SNAP:Preserved SNAP: 1.PREGANGLIONIC LESION1.PREGANGLIONIC LESION 2.WITHIN FIRST 9-10 DAYS2.WITHIN FIRST 9-10 DAYS 3.PARTIAL LESION3.PARTIAL LESION

MILD TO MODERATE lesions:side to MILD TO MODERATE lesions:side to side amplitudeside amplitude

CMAPCMAP

CMAP may require about 7-8 days to CMAP may require about 7-8 days to disappear following complete axonal disappear following complete axonal Partial nerve injuries should stabilize Partial nerve injuries should stabilize within this time frame regarding a within this time frame regarding a sequential decline in the CMAP sequential decline in the CMAP amplitude. This implies the focal amplitude. This implies the focal lesion is a static and not progressive lesion is a static and not progressive type of disorder disruption.type of disorder disruption.

collateral sprouting limits this collateral sprouting limits this parameter as a completely accurate parameter as a completely accurate predictor of axonal losspredictor of axonal loss

after several weeks.after several weeks.

EMGEMG

Helpful in delineating the lesion's extent Helpful in delineating the lesion's extent when performed about 3-4 weeks after when performed about 3-4 weeks after the presumed neural insult. the presumed neural insult.

This 3-4 week time frame is rather variable This 3-4 week time frame is rather variable and depends upon the distance between and depends upon the distance between the lesion site and muscle tissue the lesion site and muscle tissue voluntary motor units (reduced voluntary motor units (reduced recruitment) within this short time frame recruitment) within this short time frame may also be useful prior to the may also be useful prior to the detectionof membrane instability.detectionof membrane instability.

the presence of the presence of voluntary motor units voluntary motor units is also important to document because is also important to document because it signifies that the it signifies that the lesion is lesion is incomplete incomplete and neural integrity is at and neural integrity is at least partially preservedleast partially preserved

A A complete nerve transection complete nerve transection is assumed when is assumed when there is an: there is an:

1.absent CMAP 1.absent CMAP to stimulation distal to the to stimulation distal to the lesion sitelesion site

2. 2. membrane instability membrane instability to varying degrees to varying degrees depending upon the duration of injury, depending upon the duration of injury,

3. 3. no detectable voluntary motor units no detectable voluntary motor units distal to distal to the site of injury.the site of injury.

4.The corresponding 4.The corresponding SNAP, SNAP, when available, when available, may be present orabsent depending upon a may be present orabsent depending upon a preganglionic or postganglionic lesion, preganglionic or postganglionic lesion, respectively.respectively.

In the case of a very proximal lesion where no In the case of a very proximal lesion where no CMAP can be elicited, for example, it should be CMAP can be elicited, for example, it should be realized that signs of membrane instability realized that signs of membrane instability combined with absence of voluntary recruited combined with absence of voluntary recruited motor units do not necessarily indicate a complete motor units do not necessarily indicate a complete axonal lesion is present. The absence of voluntary axonal lesion is present. The absence of voluntary motor units can also be due to a motor units can also be due to a complete complete conduction blockconduction block. .

This situation may occur because the site of neural This situation may occur because the site of neural activation can be problematic in so far as the site activation can be problematic in so far as the site of nerve stimulation may be proximal to the of nerve stimulation may be proximal to the lesion's locationlesion's location

FOCAL DEMYELINATIONFOCAL DEMYELINATION

Demyelination(Demyelination(↓NCV↓NCV):):

1.1.Differential slowingDifferential slowing{{TD vs CBTD vs CB

The alteration in the CMAP is the important finding The alteration in the CMAP is the important finding suggestingsuggesting

that there is a differential slowing of neural impulse that there is a differential slowing of neural impulse propagation crossing the affected portion of nerve. propagation crossing the affected portion of nerve.

2. 2. synchronized impulse slowingsynchronized impulse slowing. The CMAP appears . The CMAP appears quite similar above and below the damaged portion quite similar above and below the damaged portion of nerve with respect to its general morphology of nerve with respect to its general morphology regarding duration and phases.regarding duration and phases.

CBCB::↓↓NCV-no same morphology above NCV-no same morphology above & below-& below-above Duration =below above Duration =below Duration Duration

TDTD:: ↓ ↓NCV-no same morphology above NCV-no same morphology above & below-& below-above Duration >below above Duration >below Duration Duration

synchronized impulse synchronized impulse slowingslowing::↓↓NCV,same morphology NCV,same morphology above & belowabove & below

HISTORYHISTORY

acute or insidiousacute or insidious disease process.disease process. All compressive nerve lesions All compressive nerve lesions that that

develop develop acutelyacutely should be treated should be treated conservatively, even if severeconservatively, even if severe

work history,Dm,CTDwork history,Dm,CTD

PHYSICAL EXAMINATIONPHYSICAL EXAMINATION

pin prick, touch, vibration, and pin prick, touch, vibration, and proprioceptionproprioception

muscle tone and deep tendon reflexesmuscle tone and deep tendon reflexes

NERVE CONDUCTION NERVE CONDUCTION STUDIESSTUDIES

Nerve conduction studies are Nerve conduction studies are extremely important in evaluating extremely important in evaluating focal peripheral neuropathies.focal peripheral neuropathies.

In addition to documenting segmental In addition to documenting segmental nerve nerve conduction velocitiesconduction velocities, it is also , it is also necessary to determine the necessary to determine the response's response's magnitude magnitude at various stimulation sites at various stimulation sites and and distal latenciesdistal latencies..

SNAP amplitude across long body SNAP amplitude across long body segments (elbow to wrist): segments (elbow to wrist): phase phase cancellation cancellation secondary to temporal secondary to temporal dispersive effects over long distances dispersive effects over long distances normally results in significant normally results in significant amplitude reductions. amplitude reductions.

Side-to-side SNAP amplitude Side-to-side SNAP amplitude comparisons over similar distancescomparisons over similar distances

Sensory Nerve Conduction Sensory Nerve Conduction Studies.Studies.

The sensory fibers are usually, though not The sensory fibers are usually, though not always, affected always, affected first and to a more first and to a more significant degree(PNP).significant degree(PNP).

SNAPs from the SNAPs from the lower limbs lower limbs even with even with exclusively exclusively upper limb upper limb complaints whenever complaints whenever there is a clinical suspicion of a possible there is a clinical suspicion of a possible concomitant peripheral neuropathy.concomitant peripheral neuropathy.

comparing a proximal and distal amplitude in comparing a proximal and distal amplitude in the same limb is of less value because of the the same limb is of less value because of the previously noted previously noted phase cancellation phase cancellation effectseffects

Motor Nerve Conduction Motor Nerve Conduction StudiesStudies

The CMAP The CMAP amp and nerve conduction amp and nerve conduction velocity are perhaps the two most useful velocity are perhaps the two most useful parametersparameters

The CMAP amplitude provides information The CMAP amplitude provides information regarding the regarding the number of functional axons number of functional axons especially when compared with the especially when compared with the comparable response on the unaffected sidecomparable response on the unaffected side

The The minor limitation minor limitation of using velocities is of using velocities is the potential for the potential for inaccurate measurement of inaccurate measurement of the distancesthe distances required for the calculation.required for the calculation.

The H-reflex is of The H-reflex is of little use little use in attempting in attempting to localize focal peripheral nerve lesions to localize focal peripheral nerve lesions distal to the root level:distal to the root level:

1. The long pathway of impulse 1. The long pathway of impulse conduction renders it susceptible to conduction renders it susceptible to compromise at any location along the compromise at any location along the afferent or efferent conduction course.afferent or efferent conduction course.

2. the H-reflex is its limited distribution 2. the H-reflex is its limited distribution to primarily the to primarily the tibial and median nervestibial and median nerves..

F-Wave. F-Wave. The most useful aspect The most useful aspect of the F-wave of the F-wave is its long neural pathway in that it is capable is its long neural pathway in that it is capable of alerting one to the fact that a lesion is of alerting one to the fact that a lesion is present at some locationpresent at some location

1. The very nature of its long pathway renders 1. The very nature of its long pathway renders this procedure nonspecific with respect to this procedure nonspecific with respect to locationlocation

2. Also, most techniques use the 2. Also, most techniques use the shortest F-shortest F-wave wave of multiple trials.of multiple trials.

This tends to This tends to predispose the results to a predispose the results to a normal studynormal study, potentially missing subtle , potentially missing subtle abnormalities early in the disease courseabnormalities early in the disease course

Somatosensory Evoked Somatosensory Evoked Potentials (SEPs).Potentials (SEPs).

In the lower limb, the In the lower limb, the lateral femoral lateral femoral cutaneous and saphenous nerves cutaneous and saphenous nerves may may be more amenable to evaluation with be more amenable to evaluation with SEPs, while the SEPs, while the lower lateral lower lateral cutaneouscutaneousor or posterior cutaneous posterior cutaneous nerve nerve of the forearm in the upper limbof the forearm in the upper limb

LATENCY LATENCY ≥≥ AMPLITUDE AMPLITUDE

Mixed Nerve Stimulation.Mixed Nerve Stimulation.

The exact fiber population contributing The exact fiber population contributing to the potential's onset, to the potential's onset, fastest fastest conducting conducting fibers, is unclear and may fibers, is unclear and may be a mixture of be a mixture of motor and sensory motor and sensory axonsaxons, or , or pure sensory axons.pure sensory axons.

NEEDLE NEEDLE ELECTROMYOGRAPHYELECTROMYOGRAPHY

The The most reliable most reliable finding : finding : positive sharp waves and positive sharp waves and fibrillation potentialsfibrillation potentials in a distribution compatible in a distribution compatible with an individual peripheral nerve as opposedto a with an individual peripheral nerve as opposedto a root or plexus pattern.root or plexus pattern.

NL EMGNL EMG::

1.peripheral nerve trunks contain multiple funiculi1.peripheral nerve trunks contain multiple funiculi

2.Membrane instability also tends to be 2.Membrane instability also tends to be self-inhibitingself-inhibiting

3.The needle electrode is placed in a 3.The needle electrode is placed in a partially partially denervateddenervated muscle and not located in the portion muscle and not located in the portion of this muscle containing the denervated fibersof this muscle containing the denervated fibers

44.Anomalous innervation.Anomalous innervation

MUAP morphologic MUAP morphologic changes and changes and alterations in alterations in recruitmentrecruitment may also be may also be of assistance in diagnosing focal of assistance in diagnosing focal peripheral neuropathies.peripheral neuropathies.

ANATOMY of median nerveANATOMY of median nerve

lateral and medial cordslateral and medial cords→→each give off each give off a major terminal branch, lateral and a major terminal branch, lateral and medial root of the median nerve, medial root of the median nerve, respectively, which fuse about the respectively, which fuse about the axillary artery to form the median axillary artery to form the median nervenerve (C5, C6, and C7,C8 and T I) (C5, C6, and C7,C8 and T I)

5 cm proximal to flex.retinaculom : Medial 5 cm proximal to flex.retinaculom : Medial to FCR & LATERAL to P.longto FCR & LATERAL to P.long

carpal tunnelcarpal tunnel:: EightEight tendons of the tendons of the superficial and superficial and

deep deep finger flexors, and the the finger flexors, and the the flexor flexor pollicis longuspollicis longus tendon and tendon and median median nervenerve

Neural BranchingNeural Branching The The first muscular first muscular branch to arise from the branch to arise from the

median nerve is to the median nerve is to the pronator teres pronator teres 40-58%40-58%,the branch to the pronator teres muscle ,the branch to the pronator teres muscle

originates originates proximal to the medial epicondyleproximal to the medial epicondyle.. The next muscular branch off the median nerve The next muscular branch off the median nerve

is to the is to the flexor carpi radialisflexor carpi radialis Palmaris logusPalmaris logus The The flexor digitorum superficialis flexor digitorum superficialis muscle is then muscle is then

innervated by either a separate branch from the innervated by either a separate branch from the main median nerve main median nerve trunk,or from trunk,or from multiple multiple branches supplying the flexor carpi radialis branches supplying the flexor carpi radialis and and occasionally the occasionally the pronator teres pronator teres musclesmuscles

Approximately Approximately 2-8 (mean 5.1) cm 2-8 (mean 5.1) cm distal to distal to the medial epicondyle,the relatively large the medial epicondyle,the relatively large anterior interosseous nerve originates anterior interosseous nerve originates from the median nerve trunk to course from the median nerve trunk to course distally and distally and superficial to superficial to the FDPthe FDP

The The first muscle first muscle supplied by the A. I.O is supplied by the A. I.O is the flexor digitorum profundusthe flexor digitorum profundus

Flexor pollicis longus Flexor pollicis longus And And pronator pronator quadratus quadratus

The last branch The last branch given off by the main trunk of given off by the main trunk of the median nervein the forearm is the the median nervein the forearm is the palmar palmar cutaneous branch of the median nerve.cutaneous branch of the median nerve.

cutaneous sensation to the cutaneous sensation to the bases of the thenar bases of the thenar and and hypothenar eminencies hypothenar eminencies as well as a small as well as a small area of skin in the area of skin in the mid-palmmid-palm region. region.

It may also be completely absent, in which It may also be completely absent, in which case case lateral antebrachial cutaneous lateral antebrachial cutaneous (musculocutaneous) and superficial radial (musculocutaneous) and superficial radial nervesnerves and occasionally with the and occasionally with the palmar palmar cutaneous branch of the ulnar cutaneous branch of the ulnar provide provide sensibility to sensibility to bases of the thenar bases of the thenar ..

the carpal tunnel is bounded by the carpal tunnel is bounded by four carpal four carpal bonesbones and a and a tough transverse carpal tough transverse carpal ligamentligament

Before entering the carpal tunnel, the Before entering the carpal tunnel, the median nerve is roughly cylindrical to oval median nerve is roughly cylindrical to oval in shape.in shape.

Just prior to reaching the distal edge of the Just prior to reaching the distal edge of the transverse carpal ligament, the median transverse carpal ligament, the median nerve splits into nerve splits into laterallateral and and medial limbs medial limbs a a thenar or recurrent (motor) branchthenar or recurrent (motor) branch

lateral limblateral limb:: →→first common palmar digital nerve first common palmar digital nerve → three proper → three proper

digital nerves with two branches supplying the volar digital nerves with two branches supplying the volar aspect of the first digit and thenar eminence, and a aspect of the first digit and thenar eminence, and a third innervating the radial portion of the second digit third innervating the radial portion of the second digit and first lumbrical muscle.and first lumbrical muscle.

medial limbmedial limb:: → → second common palmar digital second common palmar digital → 2nd lumbrical → 2nd lumbrical

muscle → proper digital n → cutaneous sensation to muscle → proper digital n → cutaneous sensation to the adjacent sides of the second and third digits.the adjacent sides of the second and third digits.

→ → third common palmar digital third common palmar digital → skin between the → skin between the third and fourth digits supplying the radial half of the third and fourth digits supplying the radial half of the fourth digit and third lumbrical.fourth digit and third lumbrical.

Arm RegionArm Region humeral fractures, lacerations, bullet wounds, brachial artery-humeral fractures, lacerations, bullet wounds, brachial artery-

cephalic vein fistulas, and compression from: prolonged cephalic vein fistulas, and compression from: prolonged tourniquet application, rifle slings, anomalous muscles, tourniquet application, rifle slings, anomalous muscles, hanging over chair backs (hanging over chair backs (sleep/Saturday night palsiessleep/Saturday night palsies),and a ),and a person's head (person's head (honeymoon palsies)honeymoon palsies)

complete median nerve injury in the arm results in loss of complete median nerve injury in the arm results in loss of median innervation to muscles distal to the lesion site median innervation to muscles distal to the lesion site beginning with the pronator teres beginning with the pronator teres

hand weakly flexing, hand weakly flexing, deviating in the ulnar direction deviating in the ulnar direction ssecondary to the unopposed action of the econdary to the unopposed action of the flexor carpiulnarisflexor carpiulnaris

trick" movementstrick" movements:pronate the forearm:pronate the forearm benediction signbenediction sign

Thenar atrophy: Thenar atrophy: hollowed outhollowed out Palmar abduction of the thumb Palmar abduction of the thumb

((movement of the thumb at right movement of the thumb at right angles to the palmangles to the palm) is severely limited) is severely limited

Thumb opposition to the fifth digit is Thumb opposition to the fifth digit is impossible,impossible,

Sensory lossSensory loss

Electrophysiologic Evaluation Electrophysiologic Evaluation and Findingsand Findings..

Median SNAP from Median SNAP from digits 1-4digits 1-4.. most focal median neuropathies proximal to most focal median neuropathies proximal to

the wrist:the wrist:second or third second or third the most commonly the most commonly Antidromic techniques Antidromic techniques usually yield more usually yield more easily obtained responseseasily obtained responses

Amplitude reductions with mild Amplitude reductions with mild prolongations in latencyprolongations in latency

Side-to-side comparisons Side-to-side comparisons of both amplitude of both amplitude and latency (conduction velocity) are the and latency (conduction velocity) are the two important parameters evaluated.two important parameters evaluated.

median SNAP from the second or third median SNAP from the second or third digit displaying a digit displaying a reduced amplitude reduced amplitude and possibly prolonged latency.and possibly prolonged latency.

ulnar and sup radial SNAPulnar and sup radial SNAP

CMAP from the APB is the most common CMAP from the APB is the most common median median motor nerve technique.motor nerve technique.

A lesion in the arm would be expected to result in a A lesion in the arm would be expected to result in a CMAP reduction when obtained from wrist CMAP reduction when obtained from wrist stimulation and as compared with the contralateral stimulation and as compared with the contralateral side.side.

In arm lesions, stimulate in In arm lesions, stimulate in the axilla the axilla as well as in as well as in the the antecubital fossa antecubital fossa or just or just proximal to this proximal to this site, site, i.e., the distal armi.e., the distal arm

CMAP obtained with axilla stimulation is CMAP obtained with axilla stimulation is significantly less than 80% of that with elbow significantly less than 80% of that with elbow excitation,excitation,→→ conduction block→good prognosisconduction block→good prognosis

A reduced amplitude at all stimulation sites, but no A reduced amplitude at all stimulation sites, but no drop in NCV across the arm, is suggestive of an drop in NCV across the arm, is suggestive of an injury producing primarily axonal lossinjury producing primarily axonal loss

wait wait about 2-4 weeks about 2-4 weeks prior to performing the needle prior to performing the needle electromyographic examination depending upon the distance electromyographic examination depending upon the distance between the lesion and muscle tissue.between the lesion and muscle tissue.

membrane instability membrane instability can be expected in all muscles innervated can be expected in all muscles innervated by the median nerve beginning with the pronator teresby the median nerve beginning with the pronator teres

Performing the needle examination prior to the development of Performing the needle examination prior to the development of membrane instability only membrane instability only reveals recruitment abnormalities reveals recruitment abnormalities provided the lesion has affected a sufficient number of axons.provided the lesion has affected a sufficient number of axons.

motor conduction studies and needle electromyographic motor conduction studies and needle electromyographic evaluation should be performed on more than just median-evaluation should be performed on more than just median-innervated musclesinnervated muscles

It is entirely possible to It is entirely possible to find positive sharp waves and find positive sharp waves and fibrillation potentials in radial and ulnar innervated musclesfibrillation potentials in radial and ulnar innervated muscles despite corresponding "normal”CMAPs and SNAPsdespite corresponding "normal”CMAPs and SNAPs

Distal Arm/Proximal Forearm Distal Arm/Proximal Forearm RegionRegion

Fractures and DislocationsFractures and Dislocations:: Supracondylar fractures of the humerus Supracondylar fractures of the humerus → → axonal loss axonal loss

and reduced conduction and reduced conduction →→primarily the primarily the radial nerveradial nerve, , less commonly the median nerve, and only occasionally less commonly the median nerve, and only occasionally the ulnar nervethe ulnar nerve

axonal loss or conduction blockaxonal loss or conduction block Obtainable responses and voluntary motor units defines Obtainable responses and voluntary motor units defines

a nerve lesion as a nerve lesion as incomplete.incomplete. Absent clinical function Absent clinical function but obtainable but obtainable SNAPs and SNAPs and

CMAPs greater than 10 days CMAPs greater than 10 days after the injury→some after the injury→some component of conduction blockcomponent of conduction block

Membrane instability Membrane instability in muscles innervated by the in muscles innervated by the different major nerves of the affected limbdifferent major nerves of the affected limb

Disappearance of membrane instability Disappearance of membrane instability combined with combined with increases in muscle strength →increases in muscle strength →reinnervationreinnervation

SupracondylarSupracondylar Spur and Spur and Ligament of Ligament of StruthersStruthers

3-6 cm proximal 3-6 cm proximal to the humerus' medial epicondyle, a bony to the humerus' medial epicondyle, a bony spurspur less than 2 cm in length can arise from the anteromedial less than 2 cm in length can arise from the anteromedial aspect of the humerus in 0.7-2.7% of the populationaspect of the humerus in 0.7-2.7% of the population

fibrous or fibro-osseous ligament fibrous or fibro-osseous ligament (ligament of Struthers) (ligament of Struthers) usually extends distally from the spur to attach to the medial usually extends distally from the spur to attach to the medial epicondyleepicondyle

insidious onset of weakness insidious onset of weakness primarily :hand's ability to hold primarily :hand's ability to hold onto objects as well as difficulty flexing the wrist against onto objects as well as difficulty flexing the wrist against resistance.resistance.

DTR:DTR: preserved except for hand pronation and finger flexion preserved except for hand pronation and finger flexion to the to the second and third digitsecond and third digit →→profound nerve damageprofound nerve damage

Tinel's signTinel's sign Muscle testing Muscle testing reveals mild to moderate weaknessreveals mild to moderate weakness Test the flexor pollicis longus :Test the flexor pollicis longus : innervated by the A.I.N and innervated by the A.I.N and

when affected in combination with the hand intrinsic/extrinsic when affected in combination with the hand intrinsic/extrinsic muscles implies a muscles implies a lesion proximal to the formation of this lesion proximal to the formation of this nerve, i.e., arm or proximal forearmnerve, i.e., arm or proximal forearm..

Treatment:Treatment: conservativeconservative surgical →surgical → 1.From time to time, there may be an ssociated 1.From time to time, there may be an ssociated

fracture of the supracondylar spur from trauma fracture of the supracondylar spur from trauma or muscular forces, and if associated with neural or muscular forces, and if associated with neural injury, again operative intervention should be injury, again operative intervention should be considered.considered.

2.Most chronic compressions with 2.Most chronic compressions with electrodiagnostic medicine evidence of axonal electrodiagnostic medicine evidence of axonal loss or profound clinical symptomsloss or profound clinical symptoms

Bicipital Aponeurosis (Lacertus Bicipital Aponeurosis (Lacertus Fibrosus)Fibrosus)

thickening of the thickening of the antebrachial fascia antebrachial fascia that serves to that serves to attach the biceps brachii muscle to the ulnaattach the biceps brachii muscle to the ulna

Median nerve SNAPs Median nerve SNAPs →→reduced amplitude (reduced amplitude (absent in absent in long-standing disease )long-standing disease )

The thenar CMAP amplitude: is reducedThe thenar CMAP amplitude: is reduced Stimulating both above and below the elbow region Stimulating both above and below the elbow region

demonstrates a slowing of conduction in chronic demonstrates a slowing of conduction in chronic cases where there has been cases where there has been demyelination/remyelination changes.(Nl forearm demyelination/remyelination changes.(Nl forearm NCV)NCV)

membrane instability membrane instability →→ not only the main trunk of not only the main trunk of the median nerve but also the anterior interosseous the median nerve but also the anterior interosseous nervenerve

pronator terespronator teres surgical explorationsurgical exploration

Pronator Teres SyndromePronator Teres Syndrome sublimis bridge sublimis bridge or or fibrous arch fibrous arch of the FDSof the FDS The median nerve :compromised as it passes The median nerve :compromised as it passes through the through the

pronator teres muscle, or about the sublimis pronator teres muscle, or about the sublimis bridgebridge→→"kinking”on passage through this region or by "kinking”on passage through this region or by constricting anomalous fibrous bands crossing the two constricting anomalous fibrous bands crossing the two heads of the FDSheads of the FDS

DDx: Grocery-bag neuropathyDDx: Grocery-bag neuropathy insidious onset of a diffuse type of dull, aching pain about insidious onset of a diffuse type of dull, aching pain about

the proximal forearm exacerbated by forced forearm the proximal forearm exacerbated by forced forearm pronation.pronation.

Unlike carpal tunnel syndrome, Unlike carpal tunnel syndrome, nocturnal awakening nocturnal awakening secondary to pain and paresthesias is absent or secondary to pain and paresthesias is absent or occasionaloccasional..

Tinel's sign Tinel's sign about the elbow is a rather common findingabout the elbow is a rather common finding

Diminution or absence of median Diminution or absence of median evoked evoked SNAPs SNAPs from the first through fourth digits.from the first through fourth digits.

axonal loss→axonal loss→decreased CMAP ampdecreased CMAP amp Median NCV over the forearm Median NCV over the forearm segment can segment can

be abnormal; however, this is not a be abnormal; however, this is not a consistent finding, particularly in less than consistent finding, particularly in less than severe casessevere cases

Active isometric forearm pronation is used Active isometric forearm pronation is used to produce abnormal neural conduction to produce abnormal neural conduction supposedly through a mechanism of supposedly through a mechanism of reversible conduction blockreversible conduction block

Membrane instability can be anticipated in Membrane instability can be anticipated in all median-innervated muscles all median-innervated muscles distal to the distal to the pronator teres pronator teres

Treatment consists of initially Treatment consists of initially attempting a conservative regimen attempting a conservative regimen of avoiding the offending repetitive of avoiding the offending repetitive trauma, rest, and corticosteroid trauma, rest, and corticosteroid infiltration of the pronator teres infiltration of the pronator teres musclemuscle

surgical release of the pronator surgical release of the pronator teres muscleteres muscle

Anterior Interosseous Nerve Anterior Interosseous Nerve (Kiloh-Nevin Syndrome)(Kiloh-Nevin Syndrome)

spontaneous (idiopathic),neuralgic amyotrophy, spontaneous (idiopathic),neuralgic amyotrophy, forearm/humeral fractures, muscular exertion of forearm/humeral fractures, muscular exertion of the forearm muscles, injection injuries, the forearm muscles, injection injuries, gunshot,wounds, elbow arthroscopy, gunshot,wounds, elbow arthroscopy, lacerations, pregnancy, and anomalous fibrous lacerations, pregnancy, and anomalous fibrous band compression or band compression or accessory head of the accessory head of the flexor pollicis longus muscle flexor pollicis longus muscle (Gontzer's muscle).(Gontzer's muscle).

The weakness is quite characteristic in that only The weakness is quite characteristic in that only three muscles : FPL,PQ, and flexor digitorum three muscles : FPL,PQ, and flexor digitorum profundus to the profundus to the second and third digsecond and third digits.its.

Patients usually complain of Patients usually complain of difficulty in difficulty in attempting to attempting to pick up pick up small objects with the small objects with the first two digitsfirst two digits..

P/EP/E SensationSensation :intact in the affected limb. :intact in the affected limb. MMT MMT : must be properly performed to elicit : must be properly performed to elicit

weakness in the appropriate distributionweakness in the appropriate distribution For the first digit, the For the first digit, the MCP joint is braced in MCP joint is braced in

extension extension by the examiner and the patient is asked by the examiner and the patient is asked to flex just the distal phalanxto flex just the distal phalanx→→FPL(MOST RELIABLE). FPL(MOST RELIABLE).

A similar maneuver is performed for the remaining A similar maneuver is performed for the remaining digits while also digits while also stabilizing the proximal IP stabilizing the proximal IP joint. joint. This procedure eliminates the flexor digitorum This procedure eliminates the flexor digitorum superficialis muscle and isolates the flexor superficialis muscle and isolates the flexor digitorum profundus muscle's action on the terminal digitorum profundus muscle's action on the terminal phalanx. phalanx. A patient with a lesion to the anterior A patient with a lesion to the anterior interosseous nerve will be unable to exert much in interosseous nerve will be unable to exert much in the way of terminal phalanx flexion.the way of terminal phalanx flexion.

The PQ’ clinical function is The PQ’ clinical function is difficult to isolate difficult to isolate from the from the pronator teres, but this can be attempted by flexing pronator teres, but this can be attempted by flexing the forearm and asking the patient to resist supination. the forearm and asking the patient to resist supination.

A useful clinical testA useful clinical test is to ask the patient to forcefully is to ask the patient to forcefully approximate the finger pulps of the first and second approximate the finger pulps of the first and second digits in the digits in the "OK" sign"OK" sign

weakness of the flexor pollicis longus and variable weakness of the flexor pollicis longus and variable sparing of the pronator quadratus and profundi sparing of the pronator quadratus and profundi muscles suggesting a partial anterior interosseous muscles suggesting a partial anterior interosseous syndromesyndrome

long finger flexors were primarily innervated by the long finger flexors were primarily innervated by the ulnar nerveulnar nerve

pronator quadratus muscle is overwhelmed by the pronator quadratus muscle is overwhelmed by the pronator teres muscle because of poor testing pronator teres muscle because of poor testing procedures or other reasons.procedures or other reasons.

Rarely, the fascicles destined to become the Rarely, the fascicles destined to become the anterior interosseous nerve may be anterior interosseous nerve may be preferentially injured more proximally in the preferentially injured more proximally in the median nerve where they are tightly grouped.median nerve where they are tightly grouped.

These cases present exactly like a lesion more These cases present exactly like a lesion more distally affecting solely the anterior interosseous distally affecting solely the anterior interosseous nerve despite an injury to the proximal median nerve despite an injury to the proximal median nerve trunk such as in humeral fractures.→ nerve trunk such as in humeral fractures.→ (STIR) (STIR) can reveal muscle denervation in only the can reveal muscle denervation in only the anterior interosseous nerve distribution.anterior interosseous nerve distribution.

Electrophysiologic Electrophysiologic Evaluation and Findings.Evaluation and Findings.

All SNAPsAll SNAPs →NL→NL CMAP→ P.QuadratusCMAP→ P.Quadratus A mean onset latency for the CMAP is 3.6 ± A mean onset latency for the CMAP is 3.6 ±

0.4 ms (2.9-4.4 ms) with a side-to-side 0.4 ms (2.9-4.4 ms) with a side-to-side difference of 0.0-0.4 msdifference of 0.0-0.4 ms

The baseline-to-peak amplitude is 3.1± 0.8 The baseline-to-peak amplitude is 3.1± 0.8 mV (2.0-5.5 mV) with a side-to-side mV (2.0-5.5 mV) with a side-to-side difference difference 0-25%0-25%

membrane instability in the three muscles membrane instability in the three muscles innervated by the anterior interosseous nerveinnervated by the anterior interosseous nerve

A.I.N LESION with Martin-GruberA.I.N LESION with Martin-Gruber

Martin-Gruber anastomosis Martin-Gruber anastomosis conveys fibers to conveys fibers to the ulnar nerve→innervate the first through the ulnar nerve→innervate the first through third dorsal interossei ,adductor pollicis and third dorsal interossei ,adductor pollicis and occasionally the abductor digiti minimi musclesoccasionally the abductor digiti minimi muscles

Associated weakness of second and fifth digit Associated weakness of second and fifth digit abduction as well as adduction of the first digit. abduction as well as adduction of the first digit. Membrane instability is observed not only in Membrane instability is observed not only in the anticipated three muscles innervated by the anticipated three muscles innervated by the anterior interosseous nerve, but also in the the anterior interosseous nerve, but also in the ulnar-innervated hand intrinsic muscles.ulnar-innervated hand intrinsic muscles.

the ulnar nerve's palmar digital and dorsal ulnar the ulnar nerve's palmar digital and dorsal ulnar cutaneous SNAPs are normal, as is conduction cutaneous SNAPs are normal, as is conduction across the elbow.across the elbow.

Rheumatoid arthritis → experience Rheumatoid arthritis → experience painless tendon ruptures of the flexor painless tendon ruptures of the flexor pollicis longus and flexor digitorum pollicis longus and flexor digitorum profundus muscles to the index finger, profundus muscles to the index finger, thus simulating an anterior thus simulating an anterior interosseous nerve injury.interosseous nerve injury.

Treatment for the anterior Treatment for the anterior interosseous entrapment syndrome is interosseous entrapment syndrome is at first conservative.at first conservative.

Forearm Nerve lesionsForearm Nerve lesions Elevated pressures Elevated pressures in the flexor forearm compartment in the flexor forearm compartment

((Volkmann‘s ischemic contractureVolkmann‘s ischemic contracture) secondary to ) secondary to hemorrhage in hemophiliacs from arterial/venous hemorrhage in hemophiliacs from arterial/venous punctures, and generalized trauma, nerve entrapment punctures, and generalized trauma, nerve entrapment in radius/ulna fracture fragments, direct needle in radius/ulna fracture fragments, direct needle injuries, and arteriovenous fistulas.injuries, and arteriovenous fistulas.

Patients mayor may not complain of painPatients mayor may not complain of pain, but the , but the motor and sensory consequences of median nerve motor and sensory consequences of median nerve insult are noted quite easily. insult are noted quite easily.

Physical examination demonstrates diminished Physical examination demonstrates diminished sensation in the hand consistent with a median nerve sensation in the hand consistent with a median nerve injury, as does weakness of the thenar muscles injury, as does weakness of the thenar muscles innervated by this nerveinnervated by this nerve

Abnormalities in the median evoked SNAPs from the Abnormalities in the median evoked SNAPs from the digits. Reduction in the APB's CMAP →lesions severe digits. Reduction in the APB's CMAP →lesions severe enough to produce axonal loss.enough to produce axonal loss.