Transcript Focal Peripheral Neuropathies

Focal Peripheral
Neuropathies
Chapter 24
Alireza Ashraf, M.D.
Professor of Physical Medicine & Rehabilitation
Shiraz Medical school
Entrapment within a compartment of
relatively fixed size, compression by an
internal or external source, repetitive
trauma and
overuse, or some other etiology affecting a
nerve over a finite segment is one of the
most common lesions evaluated by an
electrodiagnostic medicine consultant.
AXONAL LOSS
SNAP for approximately 9-10 days
 compound muscle action potential (CMAP)
disappears by day 7-8 because of
neuromuscular junction transmission failure
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SNAP
Preserved SNAP:
 1.PREGANGLIONIC LESION
 2.WITHIN FIRST 9-10 DAYS
 3.PARTIAL LESION
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MILD TO MODERATE lesions:side to side
amplitude
CMAP
CMAP may require about 7-8 days to
disappear following complete axonal
Partial nerve injuries should stabilize
within this time frame regarding a
sequential decline in the CMAP amplitude.
This implies the focal lesion is a static and
not progressive type of disorder
disruption.
collateral sprouting limits this parameter as a
completely accurate predictor of axonal loss
after several weeks.
EMG
Helpful in delineating the lesion's extent when
performed about 3-4 weeks after the
presumed neural insult.
This 3-4 week time frame is rather variable
and depends upon the distance between
the lesion site and muscle tissue voluntary
motor units (reduced recruitment) within
this short time frame may also be useful
prior to the detectionof membrane
instability.
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the presence of voluntary motor units is
also important to document because it
signifies that the lesion is incomplete and
neural integrity is at least partially
preserved
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A complete nerve transection is assumed
when there is an:
1.absent CMAP to stimulation distal to the
lesion site
2. membrane instability to varying degrees
depending upon the duration of injury,
3. no detectable voluntary motor units
distal to the site of injury.
4.The corresponding SNAP, when available,
may be present orabsent depending upon a
preganglionic or postganglionic lesion,
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In the case of a very proximal lesion where no
CMAP can be elicited, for example, it should
be realized that signs of membrane instability
combined with absence of voluntary recruited
motor units do not necessarily indicate a
complete axonal lesion is present. The
absence of voluntary motor units can also be
due to a complete conduction block.
This situation may occur because the site of
neural activation can be problematic in so far
as the site of nerve stimulation may be
FOCAL DEMYELINATION
Demyelination(↓NCV):
1.Differential slowing{TD vs CB
The alteration in the CMAP is the important
finding suggesting
that there is a differential slowing of neural
impulse propagation crossing the affected
portion of nerve.
2. synchronized impulse slowing. The CMAP
appears quite similar above and below the
damaged portion of nerve with respect to
CB:↓NCV-no same morphology above &
below-above Duration =below
Duration
 TD: ↓NCV-no same morphology above &
below-above Duration >below
Duration
 synchronized impulse
slowing:↓NCV,same morphology above &
below
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HISTORY
acute or insidious
 disease process.
 All compressive nerve lesions that
develop acutely should be treated
conservatively, even if severe
 work history,Dm,CTD
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PHYSICAL EXAMINATION
pin prick, touch, vibration, and
proprioception
 muscle tone and deep tendon reflexes
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NERVE CONDUCTION STUDIES
Nerve conduction studies are extremely
important in evaluating focal peripheral
neuropathies.
 In addition to documenting segmental
nerve conduction velocities, it is also
necessary to determine the response's
magnitude at various stimulation sites
and distal latencies.
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SNAP amplitude across long body segments
(elbow to wrist): phase cancellation
secondary to temporal dispersive effects
over long distances normally results in
significant amplitude reductions.
 Side-to-side SNAP amplitude
comparisons over similar distances
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Sensory Nerve Conduction
Studies.
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The sensory fibers are usually, though not
always, affected first and to a more
significant degree(PNP).
SNAPs from the lower limbs even with
exclusively upper limb complaints
whenever there is a clinical suspicion of a
possible concomitant peripheral
neuropathy.
comparing a proximal and distal amplitude
in the same limb is of less value because of
Motor Nerve Conduction Studies
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The CMAP amp and nerve conduction
velocity are perhaps the two most useful
parameters
The CMAP amplitude provides information
regarding the number of functional
axons especially when compared with the
comparable response on the unaffected
side
The minor limitation of using velocities
is the potential for inaccurate
The H-reflex is of little use in attempting
to localize focal peripheral nerve lesions
distal to the root level:
 1. The long pathway of impulse conduction
renders it susceptible to compromise at any
location along the afferent or efferent
conduction course.
 2. the H-reflex is its limited distribution to
primarily the tibial and median nerves.
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F-Wave. The most useful aspect of
the F-wave is its long neural pathway in
that it is capable of alerting one to the fact
that a lesion is present at some location
1. The very nature of its long pathway
renders this procedure nonspecific with
respect to location
2. Also, most techniques use the shortest
F-wave of multiple trials.
This tends to predispose the results to a
normal study, potentially missing subtle
Somatosensory Evoked
Potentials (SEPs).
In the lower limb, the lateral femoral
cutaneous and saphenous nerves may be
more amenable to evaluation with SEPs,
while the lower lateral cutaneousor
posterior cutaneous nerve of the forearm in
the upper limb
 LATENCY ≥ AMPLITUDE
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Mixed Nerve Stimulation.
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The exact fiber population contributing to
the potential's onset, fastest
conducting fibers, is unclear and may be
a mixture of motor and sensory
axons, or pure sensory axons.
NEEDLE ELECTROMYOGRAPHY
The most reliable finding : positive sharp waves and
fibrillation potentials in a distribution compatible with an
individual peripheral nerve as opposedto a root or plexus
pattern.
NL EMG:
1.peripheral nerve trunks contain multiple funiculi
2.Membrane instability also tends to be self-inhibiting
3.The needle electrode is placed in a partially
denervated muscle and not located in the portion of this
muscle containing the denervated fibers
4.Anomalous innervation
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MUAP morphologic changes and
alterations in recruitment may also be of
assistance in diagnosing focal peripheral
neuropathies.
ANATOMY of median
nerve
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lateral and medial cords→each give off a
major terminal branch, lateral and medial
root of the median nerve, respectively,
which fuse about the axillary artery to form
the median nerve (C5, C6, and C7,C8 and T
I)
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5 cm proximal to flex.retinaculom :
Medial to FCR & LATERAL to P.long
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carpal tunnel:
Eight tendons of the superficial and
deep finger flexors, and the the flexor
pollicis longus tendon and median
nerve
Neural Branching
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The first muscular branch to arise from the
median nerve is to the pronator teres
40-58%,the branch to the pronator teres
muscle originates proximal to the medial
epicondyle.
The next muscular branch off the median
nerve is to the flexor carpi radialis
Palmaris logus
The flexor digitorum superficialis
muscle is then innervated by either a separate
branch from the main median nerve trunk,or
from multiple branches supplying the flexor
Approximately 2-8 (mean 5.1) cm distal to
the medial epicondyle,the relatively large
anterior interosseous nerve originates from
the median nerve trunk to course distally
and superficial to the FDP
 The first muscle supplied by the A. I.O
is the flexor digitorum profundus
 Flexor pollicis longus And pronator
quadratus
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The last branch given off by the main trunk
of the median nervein the forearm is the
palmar cutaneous branch of the median
nerve.
cutaneous sensation to the bases of the
thenar and hypothenar eminencies
as well as a small area of skin in the midpalm region.
It may also be completely absent, in which
case lateral antebrachial cutaneous
(musculocutaneous) and superficial radial
the carpal tunnel is bounded by four carpal
bones and a tough transverse carpal
ligament
 Before entering the carpal tunnel, the
median nerve is roughly cylindrical to oval
in shape.
 Just prior to reaching the distal edge of the
transverse carpal ligament, the median
nerve splits into lateral and medial
limbs a thenar or recurrent (motor)
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lateral limb:
→first common palmar digital nerve → three proper
digital nerves with two branches supplying the volar
aspect of the first digit and thenar eminence, and a
third innervating the radial portion of the second
digit and first lumbrical muscle.
medial limb:
→ second common palmar digital → 2nd lumbrical
muscle → proper digital n → cutaneous sensation
to the adjacent sides of the second and third digits.
 → third common palmar digital → skin between
the third and fourth digits supplying the radial half
of the fourth digit and third lumbrical.
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Arm Region
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humeral fractures, lacerations, bullet wounds, brachial artery-cephalic
vein fistulas, and compression from: prolonged tourniquet application,
rifle slings, anomalous muscles, hanging over chair backs
(sleep/Saturday night palsies),and a person's head
(honeymoon palsies)
complete median nerve injury in the arm results in loss of median
innervation to muscles distal to the lesion site beginning with the
pronator teres
hand weakly flexing, deviating in the ulnar direction secondary
to the unopposed action of the flexor carpiulnaris
trick" movements:pronate the forearm
benediction sign
Thenar atrophy: hollowed out
 Palmar abduction of the thumb
(movement of the thumb at right
angles to the palm) is severely limited
 Thumb opposition to the fifth digit is
impossible,
 Sensory loss
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Electrophysiologic
Evaluation and Findings.
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Median SNAP from digits 1-4.
most focal median neuropathies proximal to
the wrist:second or third the most
commonly Antidromic techniques
usually yield more easily obtained
responses
Amplitude reductions with mild
prolongations in latency
Side-to-side comparisons of both
amplitude and latency (conduction velocity)
median SNAP from the second or third digit
displaying a reduced amplitude and
possibly prolonged latency.
 ulnar and sup radial SNAP
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CMAP from the APB is the most common
median motor nerve technique.
A lesion in the arm would be expected to result in a
CMAP reduction when obtained from wrist
stimulation and as compared with the contralateral
side.
In arm lesions, stimulate in the axilla as well as
in the antecubital fossa or just proximal to
this site, i.e., the distal arm
CMAP obtained with axilla stimulation is significantly
less than 80% of that with elbow excitation,→
conduction block→good prognosis
A reduced amplitude at all stimulation sites, but no
drop in NCV across the arm, is suggestive of an
injury producing primarily axonal loss
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wait about 2-4 weeks prior to performing the needle
electromyographic examination depending upon the distance between
the lesion and muscle tissue.
membrane instability can be expected in all muscles innervated
by the median nerve beginning with the pronator teres
Performing the needle examination prior to the development of
membrane instability only reveals recruitment abnormalities
provided the lesion has affected a sufficient number of axons.
motor conduction studies and needle electromyographic evaluation
should be performed on more than just median-innervated muscles
It is entirely possible to find positive sharp waves and
fibrillation potentials in radial and ulnar innervated
muscles despite corresponding "normal”CMAPs and SNAPs
Distal Arm/Proximal Forearm
Region
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Fractures and Dislocations:
Supracondylar fractures of the humerus → axonal loss and
reduced conduction →primarily the radial nerve, less
commonly the median nerve, and only occasionally the ulnar
nerve
axonal loss or conduction block
Obtainable responses and voluntary motor units defines a
nerve lesion as incomplete.
Absent clinical function but obtainable SNAPs and
CMAPs greater than 10 days after the injury→some
component of conduction block
Membrane instability in muscles innervated by the
different major nerves of the affected limb
Disappearance of membrane instability combined with
increases in muscle strength →reinnervation
Supracondylar Spur and
Ligament of Struthers
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3-6 cm proximal to the humerus' medial epicondyle, a bony
spur less than 2 cm in length can arise from the anteromedial aspect
of the humerus in 0.7-2.7% of the population
fibrous or fibro-osseous ligament (ligament of Struthers)
usually extends distally from the spur to attach to the medial
epicondyle
insidious onset of weakness primarily :hand's ability to hold
onto objects as well as difficulty flexing the wrist against resistance.
DTR: preserved except for hand pronation and finger flexion to the
second and third digit →profound nerve damage
Tinel's sign
Muscle testing reveals mild to moderate weakness
Test the flexor pollicis longus : innervated by the A.I.N and
when affected in combination with the hand intrinsic/extrinsic muscles
implies a lesion proximal to the formation of this nerve,
i.e., arm or proximal forearm.
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Treatment:
conservative
 surgical →
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1.From time to time, there may be an
ssociated fracture of the supracondylar spur
from trauma or muscular forces, and if
associated with neural injury, again operative
intervention should be considered.
2.Most chronic compressions with
electrodiagnostic medicine evidence of axonal
Bicipital Aponeurosis
(Lacertus Fibrosus)
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thickening of the antebrachial fascia that
serves to attach the biceps brachii muscle to the
ulna
Median nerve SNAPs →reduced amplitude
(absent in long-standing disease )
The thenar CMAP amplitude: is reduced
Stimulating both above and below the elbow region
demonstrates a slowing of conduction in chronic
cases where there has been
demyelination/remyelination changes.(Nl forearm
NCV)
membrane instability → not only the main
trunk of the median nerve but also the anterior
interosseous nerve
pronator teres
Pronator Teres Syndrome
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sublimis bridge or fibrous arch of the FDS
The median nerve :compromised as it passes
through the pronator teres muscle, or
about the sublimis bridge→"kinking”on
passage through this region or by constricting
anomalous fibrous bands crossing the two heads of
the FDS
DDx: Grocery-bag neuropathy
insidious onset of a diffuse type of dull, aching pain
about the proximal forearm exacerbated by forced
forearm pronation.
Unlike carpal tunnel syndrome, nocturnal
awakening secondary to pain and
Diminution or absence of median
evoked SNAPs from the first through
fourth digits.
 axonal loss→decreased CMAP amp
 Median NCV over the forearm
segment can be abnormal; however, this
is not a consistent finding, particularly in
less than severe cases
 Active isometric forearm pronation is used
to produce abnormal neural conduction
supposedly through a mechanism of
reversible conduction block
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Treatment consists of initially
attempting a conservative regimen of
avoiding the offending repetitive
trauma, rest, and corticosteroid
infiltration of the pronator teres muscle
 surgical release of the pronator teres
muscle
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Anterior Interosseous Nerve (KilohNevin Syndrome)
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spontaneous (idiopathic),neuralgic
amyotrophy, forearm/humeral fractures,
muscular exertion of the forearm muscles,
injection injuries, gunshot,wounds, elbow
arthroscopy, lacerations, pregnancy, and
anomalous fibrous band compression or
accessory head of the flexor pollicis
longus muscle (Gontzer's muscle).
The weakness is quite characteristic in that
only three muscles : FPL,PQ, and flexor
digitorum profundus to the second and
third digits.
Patients usually complain of difficulty in
attempting to pick up small objects
P/E
Sensation :intact in the affected limb.
 MMT : must be properly performed to elicit
weakness in the appropriate distribution
 For the first digit, the MCP joint is braced in
extension by the examiner and the patient is asked
to flex just the distal phalanx→FPL(MOST
RELIABLE).
 A similar maneuver is performed for the remaining
digits while also stabilizing the proximal IP joint.
This procedure eliminates the flexor digitorum
superficialis muscle and isolates the flexor digitorum
profundus muscle's action on the terminal phalanx.
A patient with a lesion to the anterior
interosseous nerve will be unable to exert
much in the way of terminal phalanx
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The PQ’ clinical function is difficult to isolate from
the pronator teres, but this can be attempted by
flexing the forearm and asking the patient to resist
supination.
A useful clinical test is to ask the patient to
forcefully approximate the finger pulps of the first
and second digits in the "OK" sign
weakness of the flexor pollicis longus and variable
sparing of the pronator quadratus and profundi
muscles suggesting a partial anterior interosseous
syndrome
long finger flexors were primarily innervated by the
ulnar nerve
pronator quadratus muscle is overwhelmed by the
pronator teres muscle because of poor testing
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Rarely, the fascicles destined to become
the anterior interosseous nerve may be
preferentially injured more proximally in the
median nerve where they are tightly
grouped.
These cases present exactly like a lesion
more distally affecting solely the anterior
interosseous nerve despite an injury to the
proximal median nerve trunk such as in
humeral fractures.→ (STIR) can reveal
Electrophysiologic Evaluation
and Findings.
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All SNAPs →NL
CMAP→ P.Quadratus
A mean onset latency for the CMAP is 3.6 ±
0.4 ms (2.9-4.4 ms) with a side-to-side
difference of 0.0-0.4 ms
The baseline-to-peak amplitude is 3.1± 0.8
mV (2.0-5.5 mV) with a side-to-side
difference %25-0
membrane instability in the three muscles
innervated by the anterior interosseous
A.I.N LESION with Martin-Gruber
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Martin-Gruber anastomosis conveys
fibers to the ulnar nerve→innervate the first
through third dorsal interossei ,adductor
pollicis and occasionally the abductor digiti
minimi muscles
Associated weakness of second and fifth digit
abduction as well as adduction of the first
digit. Membrane instability is observed not
only in the anticipated three muscles
innervated by the anterior interosseous nerve,
but also in the ulnar-innervated hand intrinsic
muscles.
the ulnar nerve's palmar digital and
dorsal ulnar cutaneous SNAPs are
Rheumatoid arthritis → experience painless
tendon ruptures of the flexor pollicis longus
and flexor digitorum profundus muscles to
the index finger, thus simulating an anterior
interosseous nerve injury.
 Treatment for the anterior interosseous
entrapment syndrome is at first
conservative.
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Forearm Nerve lesions
Elevated pressures in the flexor forearm
compartment (Volkmann‘s ischemic
contracture) secondary to hemorrhage in
hemophiliacs from arterial/venous punctures, and
generalized trauma, nerve entrapment in
radius/ulna fracture fragments, direct needle
injuries, and arteriovenous fistulas.
 Patients mayor may not complain of pain,
but the motor and sensory consequences of median
nerve insult are noted quite easily.
 Physical examination demonstrates diminished
sensation in the hand consistent with a median
nerve injury, as does weakness of the thenar
muscles innervated by this nerve
 Abnormalities in the median evoked SNAPs from the
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