We reviewed the most common entrapment neuropathies that practicing neurologists are likely to see in clinical practice. A good history, physical examination, and neurological examination are essential to guiding one's diagnostic evaluation, and ultimately, in assessing each patient's prognosis and treatment options.
Electrodiagnostic Protocol to Evaluate for Tarsal Tunnel Syndrome
1. Peroneal nerve
A. Peroneal motor study stimulating at the ankle, below recording from the extensor digitorum brevis muscle
B. Peroneal F-responses
2. Tibial nerve
A. Tibial motor study stimulating at the ankle and popliteal hallucis muscle.
B. Tibial F-responses
C. Medial and lateral plantar motor and sensory studies
3. Sural nerve sensory study
4. H-reflex (bilateral studies are necessary)
1. One peroneal-innervated muscle (e.g., tibialis anterior and extensor hallucis longus)
2. At least two tibial-innervated muscles distal to the tarsal tunnel (e.g., abductor hallucis and abductor digiti minimi)
3. At least two tibial-innervated muscles proximal to the tarsal tunnel (e.g., tibialis posterior and medial gastrocnemius)
4. If any muscle proximal to the tarsal tunnel is abnormal, additional muscles may need to be sampled to exclude more proximal causes (e.g., sciatic neuropathy, polyneuropathy, or lumbosacral plexopathy)
fibular neck, and popliteal fossa;
fossa; recording from the abductor
1. Which of the following would not be an expected clinical finding in a patient with median mononeuropathy at the wrist?
A. Paresthesias involving the first three fingers (and possible the lateral fourth) of the hand.
B. Numbness involving the first three fingers of the hand and thenar eminence.
C. Weakness of thumb abduction.
D. Worsening of symptoms at night.
E. Reproduction of pain and paresthesias with forced flexion of the wrist.
2. Which of the following is not a potential site of entrapment of the median nerve?
B. Ligament of Struthers.
C. Guyon's canal.
D. Sublimis bridge.
E. Lacertus fibrosus.
3. Common clinical findings suggesting ulnar nerve entrapment at the elbow include all of the following EXCEPT:
A. Numbness involving the fourth and fifth fingers of the hand.
B. Weakness of the hand.
C. Pain at the elbow that radiates along the medial aspect of the forearm.
D. Loss of deep tendon reflexes in the arm.
E. Pain with percussion of the area over the cubital tunnel.
4. One easy clinical finding that can help to exclude ulnar nerve compression at the wrist as compared to a more proximal lesion (elbow, brachial plexus, or nerve roots) would be:
A. Sensory deficits involving the palmar aspect of the fourth and fifth fingers.
B. Atrophy of the hypothenar and intrinsic hand muscles.
C. Sensory deficit involving the dorsomedial aspect of the hand.
D. Weakness of wrist flexion.
5. Which of the following would not be an expected finding with a radial neuropathy at the spiral groove?
A. Wrist drop.
B. Weakness of finger extension.
C. Weakness of elbow flexion.
D. Numbness over the dorsolateral hand.
E. Weakness of elbow extension.
6. A lesion of the posterior interosseous nerve would cause all of the following EXCEPT:
A. Weakness of wrist extension (possibly with radial deviation).
B. Numbness of the dorsolateral hand.
C. Forearm pain.
D. Weakness of finger extension.
7. Compression of the peroneal nerve at the fibular head is the most common entrapment neuropathy of the lower extremity. Clinical findings that would suggest this diagnosis include all of the following EXCEPT:
A. Weakness of foot dorsiflexion.
B. Weakness of foot inversion.
C. Weakness of foot eversion.
D. Numbness over the lateral calf and dorsum of the foot.
E. Tinel's sign at the fibular head.
8. In localizing a peroneal lesion to the fibular head, EMG study of which muscle is essential?
A. Peroneus longus.
B. Tibialis anterior.
C. Short head of biceps femoris.
D. Extensor hallucis longus.
9. Compression of the femoral nerve at the inguinal ligament can result in which of the following:
A. Weakness of knee flexion.
B. Weakness of hip adduction.
C. Weakness of hip flexion.
D. Sensory disturbance over the anteromedial thigh and medial calf.
10. Which of the following is consistent with tarsal tunnel syndrome (TTS)?
A. Sensory loss over the dorsum of the foot.
B. A Tinel's sign in the region of the medial malleolus.
C. Weakness of foot plantar flexion.
D. Ankle jerk loss on the affected side.
E. All of the above.
1. The correct answer is B. Patients presenting with symptoms suggestive of a median mononeu-ropathy at the wrist often describe paresthesias involving the first three fingers and lateral fourth finger, with numbness that is often worse at night. In fact, patients may report being awakened from sleep by wrist/hand pain, requiring them to "shake-out" their hands or run them under water. Because the median nerve innervates the APB muscle, weakness of thumb opposition may be present, as well as atrophy of the thenar eminence, in more advanced cases. Asking the patient to hold the wrists in a flexed position for approx 1 min is known as Phalen's maneuver, and although not 100% sensitive and specific, may be a useful test to confirm one's clinical suspicion of CTS. One would not expect numbness to extend to the thenar eminence in CTS, because the palmar cutaneous sensory branch, which arises proximal to the carpal tunnel and would be spared in an entrapment neuropathy at the wrist, innervates this area. Involvement of the thenar eminence or extending proximal to the wrist would suggest a more proximal median nerve injury.
2. The correct answer is C. The median nerve can potentially be entrapped at six different sites along its course through the arm. The ligament of Struthers refers to a fibrous band that may arise from the medial humerus and inserts on the medial epicondyle. The lacertus fibrosus arises from the biceps tendon and inserts on the forearm flexor muscles. The median nerve can also be compressed as it pierces the pronator teres muscle, and as it passes under the fibrous sublimis bridge of the flexor digitorum sublimis muscle. In addition, a branch of the median nerve, the AIN, can be compromised as it travels through the forearm. Isolated involvement of the AIN may occur in cases of brachial plexitis (Parsonage-Turner syndrome). Finally, the median nerve can be compressed at the wrist for a variety of reasons. Guyon's canal is a small anatomic tunnel through which the ulnar nerve passes through the wrist to innervate the hand and is not a site of median nerve entrapment.
3. The correct answer is D. Compromise of the ulnar nerve as it passes through the cubital tunnel is the second most common type of entrapment neuropathy after CTS. Patients may report pain that radiates into the ulnar forearm and hand. In some cases, only sensory symptoms may be present, manifesting as sensory loss primarily involving the fourth and fifth fingers. An early motor sign may be an inability to adduct the fifth finger (Wartenberg's sign) causing patients to report frequently "catching" of the finger when placing their hands in their pockets. Patients may develop atrophy and weakness of intrinsic hand muscle strength. Various provocative maneuvers, such as percussion (Tinel's sign) or sustained manual pressure over the cubital tunnel, can be helpful in confirming one's clinical suspicion. Because the ulnar nerve arises from the C8-T1 nerve roots and travels through the lower trunk and medial cord of the brachial plexus, none of the deep tendon reflexes commonly tested in the arm (biceps, triceps, or brachioradialis) should be affected.
4. The correct answer is E. Ulnar nerve entrapment at the wrist can present in a variety of ways. Commonly, some combination of sensory deficit involving the fourth and fifth fingers with weakness of the hypothenar and intrinsic hand muscles is present. Sensory loss over the dorsal aspect of the hand would not be a finding consistent with ulnar neuropathy at the wrist. The dorsomedial aspect of the hand is primarily innervated by the dorsal ulnar sensory cutaneous nerve, which is a sensory component of the ulnar nerve, but arises 6 to 8 cm proximal to the wrist and would not be involved in an entrapment neuropathy at the wrist. Similarly, weakness of the wrist flexors would indicate a more proximal lesion.
5. The correct answer is E. Radial neuropathy at the spiral groove commonly results from trauma to the proximal arm or from prolonged compression of the nerve that can occur when a patient falls asleep with the arm draped over the edge of a chair or bathtub. Weakness of wrist and finger extension, as well as elbow flexion, are all findings consistent with a lesion of the radial nerve at the spiral groove because these muscles are all innervated distal to the groove. A lesion at the spiral groove would also be expected to affect the function of the radial sensory nerve of the forearm, leading to numbness over the dorsal aspect of the lateral hand. Because the triceps are innervated proximal to the groove, elbow extension would be spared.
6. The correct answer is B. The posterior interosseous nerve is primarily a motor branch of the radial nerve that innervates most of the wrist and finger extensors. Because the extensor carpi radialis (long head) arises proximal to the PIN, the wrist may deviate radially with attempted extension. Elbow flexion and extension (brachioradialis and triceps) are both innervated proxi-mally to the takeoff of the PIN and are, thus, spared. Forearm pain is common because the PIN provides some sensation to the deep interosseous membrane of the forearm; however, no cutaneous sensory branches arise from it. One should reconsider the diagnosis of PIN entrapment if cutaneous sensation is impaired.
7. The correct answer is B. Weakness of foot inversion would not be an expected finding because this action is primarily mediated by the tibialis posterior muscle, which is innervated by the tibial nerve. This muscle is critical in determining whether foot drop is solely a peroneal nerve problem or a more proximal sciatic neuropathy or L5 root lesion. The other signs are all consistent with a peroneal neuropathy localizing to the fibular head involving both the superficial and deep branches.
8. The correct answer is C. The short head of the biceps femoris is the only muscle that is innervated by the peroneal nerve proximal to the fibular head and is, thus, critical to localizing a peroneal lesion to the fibular neck. The short head of biceps femoris should be normal in a compressive lesion of the peroneal nerve at the fibular head. The peroneus longus, tibialis anterior, and extensor hallucis longus are all peroneal innervated muscles distal to the fibular head and would be expected to be abnormal on EMG examination.
9. The correct answer is D. Weakness of knee flexion is a sciatic nerve mediated movement. Likewise, weakness of hip adduction, although also suggesting involvement of the L2-L4 nerve roots, is mediated by the obturator nerve. Hip flexion is mediated by the iliopsoas muscle group; however, this muscle group arises proximal to the inguinal ligament and would be expected to be spared. The medial and intermediate cutaneous nerve of the thigh and the saphenous nerves, all of which arise from the femoral nerve and would be affected in compression at the level of the inguinal ligament, mediate sensory disturbance over the anterior and medial aspect of the distal thigh as well as the medial calf. Weight gain, preexisting obesity, pregnancy, and the wearing of tight work belts may predispose to this type of injury.
10. The correct answer is B. A Tinel's sign over the tibial nerve in the region of the medial malleolus is relatively common. In TTS, sensory loss is relatively confined to the plantar aspect of the foot, not the dorsum. There is no associated weakness of foot plantar flexion, and the ankle jerk should be preserved.
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