Peripheral Neuropathies 2

Question 1

Conditions that increase the risk of carpal tunnel

Answer 1

• Female sex
• Genetic predesposition
• diabetes mellitus
• hypothyroidism
• pregnancy
• rheumatoid arthritis
• obesity
• aromatase inhibitors
• amyloidosis (less commonly)
• acromegaly (less commonly)

Question 2

Carpal tunnel syndrome: symptoms and clinical findings

Answer 2

Symptoms:

• Pain, paresthesias, or numbness in the first three digits (initially intermittent).
  Symptoms are usually worse with repetitive or sustained wrist flexion or extension (eg, typing, driving) but are also often exacerbated during sleep due to unconscious sustained wrist flexion.
  In some patients, pain may radiate up the medial forearm.
• Hand weakness, manifested by difficulties with fine manual coordination, particularly in tasks involving the thumb (more severe, long-standing disease and may be accompanied by thenar flattening)

Clinical examination:
- Sensation may or may not be abnormal in the median territory at rest.
Tinel sign is elicited by lightly percussing the median nerve at the wrist with a reflex hammer.
Phalen sign is performed by flexing and holding the wrist with some pressure at 90 degrees for 1 minute. With active nerve compression, paresthesias in the median nerve territory may be elicited with either maneuver.
- Detectable clinical weakness is usually limited to the abductor pollicis brevis, because the other muscles of the thumb (flexor pollicis brevis and adductor pollicis) receive dual innervation by both the ulnar and median nerves.
Weakness of thumb opposition can appear as the disease advances.
- Thenar atrophy may be evident

Question 3

Carpal tunnel syndrome evaluation

Answer 3

EMG/ NCS:
Patients with mild nerve compression demonstrate only sensory
slowing, whereas those with more severe compression demonstrate motor abnormalities

Loss of motor amplitudes –> motor axonal injury
might not improve with decompression, arguing for early surgical intervention

Question 4

Carpal tunnel syndrome differential diagnosis

Answer 4

● cervical radiculopathy
● Median neuropathy in the forearm (eg anterior interosseous)
● Cervical spondylotic myelopathy and cervical polyradiculopathy
● Brachial plexopathy
●Ischemic stroke
●Motor neuron disease
●Forearm or hand compartment syndrome
●Fibromyalgia
●Arthritis
●Raynaud phenomenon
●Pain from a ligamentous disruption

Question 5

Carpal tunnel syndrome treatment

Answer 5

Conservative therapy should be attempted first.
Conservative therapy consists of wrist splinting in the neutral
position at night and during activities that encourage wrist flexion and extension. Splinting can provide relief of pain and numbness within days in some patients.
Short courses of prednisone injections may also be useful for symptomatic improvement.

Surgery in patients with progressive motor injury, intractable and severe pain, or in those for whom median nerve–associated
numbness is disabling (eg, diamond cutters, microsurgeons).
The traditional or “open” approach involves transection of the transverse carpal ligament.

Question 6

Median nerve: brachial plexus contributions

Answer 6

The nerve fibers that are destined to comprise the median nerve travel in the upper, middle, and lower trunks of the brachial plexus.
These fibers will then pass through the lateral and medial cords of the brachial plexus and combine to form the median nerve.

Question 7

Median nerve function
1) in the forearm
2) after exiting carpal tunnel

Answer 7

1) In the upper portion of the forearm, the median nerve innervates four muscles (the pronator teres, flexor carpi radialis, palmaris longus, and the flexor digitorum superficialis).

The anterior interosseous nerve arises in the forearm as a peripheral nerve branch of the median nerve.
The anterior interosseous nerve innervates pronator quadratus, flexor pollicis longus, and medial heads of the flexor digitorum profundus I and II muscles.

The median nerve proper runs parallel to the anterior interosseous nerve in the forearm. In the region proximal to the wrist, the palmar cutaneous sensory branch of the median nerve provides sensation to the lateral half of the palm.

2) Upon exiting the carpal tunnel, the median nerve provides motor and sensory innervation to the hand. The muscles of the hand that are innervated by the median nerve are the abductor pollicis brevis, the flexor pollicis brevis (superficial head), the opponens pollicis, and the first and second lumbricals. Weakness of these muscles may occur in patients with severe or longstanding CTS, but the lumbricals are sometimes spared.

Sensory change (pain or numbness) involving the thenar eminence is typically not reported in CTS because the palmar cutaneous branch of the median nerve passes over, rather than through, the carpal tunnel

Question 8

Electromyography in the evaluation of carpal tunnel syndrome

Answer 8

EMG is a useful component of electrodiagnostic testing in CTS to exclude other conditions, such as polyneuropathy, plexopathy, and radiculopathy, and to assess severity of CTS if surgical decompression is being considered.
EMG is not necessary for patients who have classic signs and symptoms of CTS and confirmatory findings on NCS when there is no suspicion for other etiologies and surgery is not contemplated.

EMG assesses for evidence of pathologic changes in the muscles innervated by the median nerve. When secondary axonal loss is present, EMG may reveal either active denervation (eg, spontaneous activity such as fibrillation potentials, positive sharp waves, and fasciculation potentials) or chronic changes that indicate denervation with subsequent reinnervation (eg, changes in motor unit action potential amplitudes, durations, and recruitment).
Such findings are supportive of the diagnosis of CTS in the context of normal findings in both nonmedian-innervated muscles and proximal median nerve-innervated muscles.

Specific components of EMG to evaluate CTS include:

● Abductor pollicis brevis

● Two or more C6–C7 innervated muscles (eg, pronator teres, triceps brachii, extensor digitorum communis) to look for evidence of cervical radiculopathy

● Additional muscles are typically evaluated if the abductor pollicis brevis is abnormal. This includes median-innervated muscles proximal to the carpal tunnel (eg, flexor carpi radialis, pronator teres, flexor pollicis longus) to exclude a proximal median neuropathy and nonmedian-innervated muscles (eg, first dorsal interosseous, extensor indicis proprius) to rule out brachial plexopathy, polyneuropathy, and C8 to T1 radiculopathy.

Question 9

Electrodiagnostic grading of carpal tunnel syndrome severity

Answer 9

Question 10

Carpal tunnel syndrome and cervical radiculpathy differential

Answer 10

The most common disorder than can mimic CTS is cervical radiculopathy, particularly with C6 or C7 nerve root involvement. The symptoms may include arm pain and paresthesia that resemble those of CTS.
Features that favor cervical radiculopathy include:

*The presence of neck pain that radiates into the shoulder and arm
*Exacerbation of symptoms with neck movement
*Reduced reflexes (ie, biceps, brachioradialis, and triceps)
*Weakness of proximal arm muscles involving elbow flexion, extension, and arm pronation
*Sensory loss in the forearm or medial palm

C8 and T1 root lesions may also mimic the symptoms or signs of CTS, predominantly involving motor dysfunction.

Question 11

Anterior interosseous neuropathy

Answer 11

The anterior interosseous nerve branches off from the median nerve in the region of the elbow. It then descends the anterior forearm, innervating several muscles including the flexor pollicis longus, the deep flexors of digits 2 and 3, and pronator quadratus.
It does not subserve cutaneous sensation; thus, nerve dysfunction is characterized by weakness of this group of muscles only.
On examination, the patient cannot make a standard “O” (as in “okay”) with the thumb and forefinger.

Isolated injury to the anterior interosseous nerve is distinctly rare, although it may occur with significant trauma to the forearm.
More commonly, anterior interosseous neuropathy develops in patients who present with neuralgic amyotrophy (brachial neuritis)

Question 12

Clinical differential between ulnar neuropathy at the elbow and at the wrist

Answer 12

The extent of CLAWING of digits four and five can be worse with lesions at the wrist than at the elbow, as a result of sparing of the flexor digitorum profundus and weakness of the third and fourth lumbricals, resulting in greater MUSCLE IMBALANCE.

Question 13

Electrodiagnostic evaluation of ulnar neuropathy at the elbow

Answer 13

Typically, motor nerve conduction studies are obtained, recording from either the hypothenar eminence or first dorsal interosseous muscles, with stimulation at the wrist, below the elbow, and above the elbow.
The amplitude of the maximum compound muscle action potential in response to the distal site of stimulation at the wrist is a reasonable indication of the number of functioning motor axons, at least with acute or subacute presentations prior to reinnervation via collateral reinnervation.

Focal slowing or conduction block across the elbow provides the most compelling evidence of a localized lesion.

The presence of a normal or absent dorsal ulnar cutaneous sensory response is helpful in localizing lesions to the elbow or wrist, especially when the response is normal on the unaffected side.

Question 14

Electrodiagnostic evaluation of ulnar neuropathy at the wrist

Answer 14

The electrodiagnostic localization of ulnar neuropathy at the wrist is based upon the detection of focal motor or sensory nerve conduction slowing or block with stimulation at the wrist and no evidence of more proximal block or slowing.

A normal dorsal ulnar cutaneous sensory potential is helpful in ruling out more proximal lesions, as is the presence of normal needle EMG findings in the flexor carpi ulnaris and flexor digitorum profundus muscles.

Question 15

Ulnar nerve compression sites

Answer 15

Question 16

Radial nerve injury sites

Answer 16

Question 17

Radial neuropathy at the spiral groove clinical findings

Answer 17

Compression of the nerve in this area often occurs after prolonged pressure on the nerve. (“Saturday night palsy”)

• The triceps retains full strength but there is weakness of the wrist extensors (ie, “wrist drop”), finger extensors, and brachioradialis.
• Sensory loss over the dorsum of the hand, possibly extending up the posterior forearm, may also be present.

Associated weakness in ulnar-innervated hand muscles and in thumb abduction is also often present, the former likely related to difficulties in performing the action in the absence of the stabilizing influence of the finger extensors. Thumb abduction is affected as abductor pollicis longus is a radial-innervated muscle.

Question 18

Posterior interosseous neuropathy clinical findings

Answer 18

The posterior interosseous nerve supplies all the muscles of the posterior compartment of the forearm, except anconeus muscle (αγκωνιαίος μυς), brachioradialis muscle, and extensor carpi radialis longus muscle. In other words, it supplies the following muscles:

Extensor carpi radialis brevis muscle — deep branch of radial nerve
Extensor digitorum muscle
Extensor digiti minimi muscle
Extensor carpi ulnaris muscle
Supinator muscle — deep branch of radial nerve
Abductor pollicis longus muscle
Extensor pollicis brevis muscle
Extensor pollicis longus muscle
Extensor indicis muscle

A posterior interosseous neuropathy should be considered in patients with weakness of the finger extensors that spares the more proximal muscles including brachioradialis and extensor carpi radialis.

In severe cases, detailed examination may reveal radial deviation of the wrist with wrist extension secondary to involvement of extensor carpi ulnaris and sparing of extensor carpi radialis.
Forearm supination is also weak.

No sensory symptoms

Question 19

How to differentiate a central lesion from radial palsy

Answer 19

Relative preservation of triceps strength and sensory loss isolated to the dorsum of the hand are helpful findings indicative of radial neuropathy at the spiral groove.

The brachioradialis should also be weak in a radial nerve lesion, but is typically less affected in a central disorder.

++ Radialis sign of Strümpell

Question 20

Femoral nerve palsy clinical findings

Answer 20

• Weakness involving the quadriceps muscle group with sparing of adduction, which is mediated by the obturator nerve.
• Some patients with what appear to be isolated femoral neuropathies also have prominent iliopsoas weakness.
• Sensory loss over the anterior thigh and most of the medial thigh is typical. The sensory loss extends down the medial shin to the region of the arch of the foot due to saphenous nerve dysfunction.
• The knee jerk generally decreases or becomes unobtainable.

Question 21

Gonyalgia paresthetica

Answer 21

The infrapatellar (υποεπιγονατιδικός) branch of the saphenous nerve is damaged due to mild trauma or knee operations.
This produces the syndrome which includes sensory loss in a several centimeter diameter patch below the knee with intermittent lancinating pains.

Question 22

Femoral nerve palsy causes

Answer 22

• hip or pelvic fractures or masses within the iliacus (such as hematoma)
• iatrogenic femoral nerve injury (childbirth, procedures such as hip replacement, abdominal and pelvic surgery or laparoscopy, inguinal lymph node biopsy, femoral nerve block, and femoral artery puncture)
• diabetes mellitus

Question 23

Sciatic nerve palsy clinical findings

Answer 23

• Pain
• Weakness affecting most of the lower leg musculature, including the hamstrings.
  (Hip flexion, extension, abduction and adduction, and knee extension are normal)
• Sensory loss involves the entire fibular (peroneal), tibial, and sural territories. In the lower leg, however, the medial calf and arch of the foot may be spared secondary to innervation by the preserved saphenous nerve (a branch of the femoral nerve). Sensation is also spared above the knee both anteriorly and posteriorly.
• The knee jerk is normal, but the ankle jerk is unobtainable.

Question 24

Sciatic nerve palsy electrodiagnostic evaluation

Answer 24

Compression of the sciatic nerve may not produce significant abnormalities on EMG unless it is relatively severe.

Reduced fibular (peroneal) and sural sensory responses and a normal saphenous sensory response are identified in more severe cases.
Tibial and fibular (peroneal) motor response amplitudes also are reduced.

A denervation/reinnervation pattern in muscles supplied by the nerve, including the hamstrings, is typical.

Question 25

Common peroneal nerve palsy clinical findings

Answer 25

• Acute foot drop (difficulty dorsiflexing the foot against resistance or gravity).
• “steppage” gait.
• Paresthesias and/or sensory loss over the dorsum of the foot and lateral shin (superficial fibular (peroneal) nerve territory).

Examination typically reveals weakness in foot dorsiflexion and foot eversion (deep and superficial fibular (peroneal) nerve-innervated, respectively), with normal inversion and plantar flexion (tibial nerve).
Sensory disturbance is confined to the dorsum of the foot, including the web space between digits 1 and 2 and the lateral shin. Reflexes are normal.

Question 26

Peroneal palsy causes

Answer 26

The most frequent site of injury to the common fibular (peroneal) nerve is just below the knee as the nerve wraps around the lateral aspect of the fibula, immediately before dividing into its deep and superficial branches.
Compression at this site is frequently produced by external pressure on the nerve due to prolonged lying, such as during surgery, palmar pressure to the fibular neck during childbirth, or prolonged hospitalization.
Crossing the legs, protracted squatting, and leg casts also can cause compression at this site.

Question 27

Peroneal palsy electrodiagnostic evaluation

Answer 27

EMG and NCS are very useful for identifying fibular (peroneal) neuropathy at the fibular neck; conduction block on fibular (peroneal) motor studies may be identified at the site, even in the acute setting.
Reduction in distal motor and sensory response amplitudes can occur in severe cases, suggesting axonal injury.
Needle examination discloses abnormalities in the deep and superficial fibular (peroneal) nerve innervated muscles.

Question 28

Peroneal nerve compression sites

Answer 28

Question 29

Peroneal nerve palsy differential diagnosis

Answer 29

• L5–S1 radiculopathy (fibular mononeuropathy does not affect the deep tendon reflex at the ankle or the strength of plantar flexion)
• stroke
• motor neuron disease
• Injury to the lumbosacral plexus and sciatic nerve
• distal myopathies (eg, myotonic dystrophy)
• generalized polyneuropathies (eg, Charcot-Marie-Tooth family)

Question 30

Tarsal tunnel syndrome clinical findings

Answer 30

tibial nerve compression in the region of the ankles as the nerve passes under the transverse tarsal ligament

Aching, burning, numbness, and tingling involving the sole of the foot, the distal foot, the toes, and occasionally the heel. The pain may radiate up to the calf or higher. The discomfort is often most irritating at night, may be worse after standing, and sometimes leads to the desire to remove the shoes, even while driving.

Examination may disclose a prominent Tinel sign over the nerve posterior to the medial malleolus with sensory loss over the plantar surface of the foot, not extending onto the dorsal foot.
Atrophy of intrinsic foot musculature will be present only if the nerve injury is severe.

In general, true tarsal tunnel syndrome is most commonly diagnosed in patients with a clear history of antecedent foot trauma. Without such a history, “idiopathic” tarsal tunnel syndrome, unlike carpal tunnel syndrome, is quite rare.

Question 31

Tarsal tunnel syndrome electrodiagnostic evaluation

Answer 31

Electrodiagnostic testing may reveal prolonged tibial motor distal latencies and slowing of conduction velocities across the flexor retinaculum when recording from the medial and lateral plantar nerve territories.
Comparison studies with the unaffected extremity may be helpful in this regard.
EMG evaluation is of limited utility since the intrinsic foot muscles normally have mild degrees of denervation and chronic reinnervation. Again, comparison with the appearance of foot musculature on the contralateral limb is usually necessary.

Question 32

Meralgia paresthetica

Answer 32

Entrapment of lateral femoral cutaneous nerve as it traverses below the inguinal ligament
Some people are especially predisposed to developing meralgia paresthetica, including those with obesity, diabetes mellitus, and advanced age. Pregnant and postpartum patients are also at increased risk
Patients generally complain of paresthesias and pain that radiates down the lateral aspect of the thigh toward the knee. The pain can be quite significant. In more advanced cases, fixed sensory loss on the lateral thigh occurs.

Question 33

Meralgia paresthetica differential diagnosis

Answer 33

Femoral neuropathy and radiculopathy affecting the L2–L4 nerve roots.
Unlike meralgia paresthetica, these disorders cause motor symptoms and loss of the patellar reflex