(2)  Paresthesias and sensory loss. Paresthesias are spontaneous sensations originating from nerve fibers, which patients describe as “tingling” or “pins and needles.” Sensory loss indicates absence of normal sensation, which patients may describe as “numbness” or “like Novocain.” Paresthesias and sensory loss may occur together or independently, and either suggests PNS disease is more likely than an MSK disorder. The distribution of paresthesias or sensory loss can help to localize a nerve disorder. However, patients may report a distribution of sensory symptoms that varies from the precise anatomic distribution of an affected nerve or nerve root. Patients with CTS may complain of sensory symptoms in any of the first three hand digits and often report the entire hand is numb. Thus, failure of sensory symptoms to localize precisely to a specific nerve or nerve-root distribution should not exclude these disorders. The differential diagnosis of paresthesias and sensory loss should include central nervous system (CNS) disease, especially when pain is absent. Intermittent paresthesias also occur in normal individuals, usually related to a specific activity or limb position resulting in nerve compression, stretch, or irritation. Thus, paresthesias in isolation do not always indicate a pathologic state.

b.  Motor symptoms. Patients complaining of weakness should be asked to describe specific activities that cause difficulty. Impaired fine motor skills—for example, buttoning buttons—indicate distal muscle weakness and suggest involvement of C8 or T1 roots, lower plexus, or nerves supplying hand muscles (median or ulnar nerves). Difficulty with arm and shoulder movements indicates proximal muscle weakness, suggesting involvement of the C5 or C6 roots, upper plexus, or nerves supplying proximal muscles (e.g., long thoracic, suprascapular, axillary nerves). Patients with pain or sensory loss may misconstrue impaired motor performance as weakness. This possibility may be clarified during the exam, or asking the patient to state which factor chiefly limits physical performance. CNS disorders can also produce weakness of either the proximal or distal musculature.

2.  Onset and precipitating factors. The history should seek to identify specific activities the patient participated with during or just preceding the onset of symptoms and whether or not physical activity exacerbates the symptoms.

a.  Physical activities. Some physical activities may predispose to specific PNS disorders. Heavy lifting may precipitate cervical disk herniation and resultant radiculopathy. Head turning often exacerbates pain or paresthesias associated with radiculopathy. Arm abduction or shoulder rotation exacerbates the pain of MSK shoulder disorders and also the pain associated with brachial plexopathy. Repetitive flexion and extension movements of the elbow or sustained elbow flexion may predispose to ulnar mononeuropathy at the elbow (cubital tunnel syndrome). Repetitive flexion and extension movements at the wrist or fingers may predispose to median mononeuropathy within the carpal tunnel. Repetitive pronation and supination may lead to hypertrophy of the pronator teres muscle and median nerve entrapment in the forearm (pronator teres syndrome). The radial nerve may be compressed in the axillary region by improper use of a crutch, or in the arm when pressure is applied by a tourniquet, a hard surface, or the body’s weight. Radial nerve compression in the arm is especially likely to occur when consciousness is reduced by anesthesia, sedatives, or alcohol intoxication. Handcuffs or other tight-fitting objects at the wrist—for example, watchbands or bracelets—may injure the median, ulnar, or superficial radial sensory nerves. The history should include review of occupation, hobbies, and recent changes in physical activity. Sporting activities, playing musical instruments, gardening, and knitting are examples of physical activities that could predispose to compressive nerve injuries.

b.  Trauma often causes UE pain and sensorimotor complaints. Even remote trauma may contribute to UE pain or sensorimotor symptoms. Examples include entrapment of a nerve by the callus of a healing fracture and development of a central cavity in the spinal cord (syringomyelia).

(1)  Motor vehicle accident (MVA). The severe trauma of a MVA may cause multiple neurologic complications including vertebral fracture with direct spinal cord injury, nerve-root avulsion, radiculopathy, brachial plexus injury, peripheral nerve injury, or late development of syringomyelia. Arm traction or stretching the arm and neck in opposite directions may cause cervical root avulsions or a stretch injury to the brachial plexus. An MVA may cause more than one PNS disorder—for example, cervical nerve-root avulsions and concomitant peripheral nerve injury. After an MVA, attention to multiple life-threatening injuries, or casting for multiple limb fractures, may preclude detection of PNS disorders until late in the course of recovery.

(2)  Fractures and dislocations may cause specific nerve injuries. Shoulder dislocation or fracture of the humerus may injure the axillary nerve. Fracture of the clavicle may injure components of the brachial plexus. Fracture of the humerus predisposes to radial nerve injury in the spiral groove, whereas fracture or dislocation of the radius may injure the posterior interosseous nerve (PIN) branch of the radial nerve. Fracture of the elbow predisposes to ulnar mononeuropathy, which may not manifest until years after the trauma, hence the name “tardy ulnar palsy.” A wrist fracture may cause either median or ulnar mononeuropathy.

(3)  Laceration. When UE pain or sensorimotor symptoms begin after a skin laceration or puncture wound, direct injury to a nerve needs to be considered. Exploration is needed to determine if the nerve requires repair.

c.  Physiologic compression sites. The median and ulnar nerves are vulnerable to injury at specific sites where normal ligamentous and bony structures predispose to physical compression. The common compression sites are the wrist for the median nerve (carpal tunnel) and the elbow for the ulnar nerve (cubital tunnel). At these locations, the nerves are particularly susceptible to compression injury, hence the term “physiologic compression sites.” A patient with UE sensorimotor symptoms, without any clear predisposing factors, is likely to have an abnormality of one of these nerves.

d.  Systemic illnesses. Systemic illness may predispose to development of PNS disorders that manifest as UE sensorimotor symptoms. A complete listing of systemic illnesses with PNS complications exceeds the scope of this chapter, but several common examples are given.

(1)  Endocrine disorders. Patients with diabetic polyneuropathy are more vulnerable to development of mononeuropathies at physiologic compression sites. Patients with hypothyroidism are prone to developing CTS.

(2)  Rheumatologic disorders. Several rheumatologic disorders predispose to UE nerve or nerve-root injury. Rheumatoid arthritis causes joint and degenerative bone disease, which may lead to cervical radiculopathy, CTS, and PIN injury. Systemic vasculitis may involve individual peripheral nerves in either the upper or lower extremities. Abrupt onset of a mononeuropathy is occasionally the presenting manifestation of systemic vasculitis. Primary amyloidosis and some hereditary forms are associated with CTS.

(3)  Renal failure and dialysis. Patients receiving chronic hemodialysis are particularly likely to develop CTS, owing to deposition of amyloid material (b ₂ microglobulin) within the carpal tunnel. Placement of arteriovenous fistulas for hemodialysis may cause median or ulnar neuropathies and, less often, a severe distal ischemic injury to all UE nerves, called ischemic monomelic neuropathy. Diabetic patients seem particularly prone to this severe nerve injury.

(4)  Malignancy. A patient with a history of cancer—particularly of the breast or lung—who develops UE sensorimotor complaints needs to be evaluated for metastases to the brachial plexus. Patients with radiation therapy to the brachial plexus region can develop radiation-induced brachial plexopathy, which may begin many years after radiation therapy.

3.  Other history. The medical history should also inquire about symptoms of depression and a review of the social situation for factors that might influence the patient’s symptoms. Specific questions should be asked regarding employment, accidents, work injuries, and possible litigation. Evidence of CNS disease should be sought, which might include seizures, disturbed consciousness, personality change, or problems with cognition, language, or vision.

B.  Physical examination.

1.  Motor examination.

a.  Muscle inspection. Muscles are inspected for atrophy and spontaneous muscle contractions. Muscle atrophy is present when reduction of the normal muscle bulk is revealed by visual inspection or direct measurement of limb circumference. Atrophy of specific muscles helps localize the disorder. Atrophy of the thenar eminence alone suggests a disorder of the median nerve or the deep terminal branch of the ulnar nerve. Atrophy of the thenar and hypothenar areas and the interossei muscles should raise considerations of combined median and ulnar mononeuropathies, lower trunk brachial plexopathy, C8–T1 radiculopathy, or C8–T1 spinal cord disease. Winging or elevation of one scapula suggests a long thoracic nerve mononeuropathy. Muscle inspection also involves a careful search for fasciculations, which are fine muscle twitches visible through the skin. Fasciculations may occur infrequently as an isolated finding in asymptomatic individuals. However, when present in conjunction with muscle weakness and atrophy, fasciculations are a sign of a lower motor neuron process. The exam should include inspection for fasciculations in all four limbs, as well as in the back and abdomen. Fasciculations occur most commonly with anterior horn cell diseases—for example, amyotrophic lateral sclerosis—but can also occur with diseases affecting the motor root, plexus, or peripheral nerve.

b.  Muscle strength ratings. Muscle strength is assessed with manual muscle testing using the Medical Research Council strength rating scale (Table 22.1). Muscle strength should be tested in proximal and distal muscles in all four limbs. This allows quantification of weakness and may reveal weakness the patient was not aware of. Muscles that should be tested bilaterally in the UE include muscles for arm abduction (deltoid and supraspinatus), arm external rotation (infraspinatus), elbow flexion (biceps), elbow extension (triceps), wrist flexion (flexor carpi radialis and flexor carpi ulnaris), wrist extension (extensor carpi radialis), finger flexion (flexor digitorum superficialis and flexor digitorum profundis), finger extension (extensor digitorum communis), finger spreading (interossei), thumb abduction (abductor pollicis brevis), and grip strength.

Patients with MSK disorders and patients with depression, psychological disturbances, or malingering may exhibit a type of weakness known as “breakaway” weakness, in which incomplete effort gives the appearance of weakness. Features suggesting breakaway weakness include pain complaints during muscle strength testing, reasonable initial strength that decreases, variability in motor performance on serial exams, improved strength with encouragement, and absence of other objective signs of motor impairment. Patients with breakaway weakness due to a psychological disturbance or malingering often make facial expressions or body contortions to convey that great effort is being made.

c.  Muscle tone is assessed by noting how easily the patient’s limbs can be passively moved while the patient is asked to relax the limb tested. The tone is rated according to the Ashworth scale, in which normal tone is assigned a value of 1, and values 2 to 5 represent increasing degrees of abnormal stiffness. Muscle tone should be normal with all of the common PNS disorders causing UE pain and sensorimotor symptoms. Increased muscle tone raises the question of a CNS disorder. When increased muscle tone occurs with UE weakness and atrophy, the possibility of upper motor neuron disease needs to be considered. Considerations should include a compressive lesion of the cervical spine such as spinal stenosis, metabolic disorders such as B₁₂ deficiency or copper deficiency, or amyotrophic lateral sclerosis.

2.  Reflexes are tested bilaterally in all four limbs, including the brachioradialis (C5–C6), biceps (C5–C6), triceps (C7–C8), quadriceps (L2–L4), and soleus (S1) tendons. Reflexes are rated as normal, decreased, or increased. A significant reflex asymmetry suggests an abnormality of the nervous system. Radiculopathy involving a cervical root typically depresses the corresponding UE reflex on the affected side. Brachial plexopathy causes decreased reflexes corresponding to the part of the plexus involved. Patients with C8–T1 radiculopathy or lower trunk brachial plexopathy may exhibit normal UE reflexes. Mononeuropathies of the UE do not usually influence the UE reflexes, unless the nerve involved supplies the muscle tested in the reflex arc—for example, musculocutaneous nerve mononeuropathy may cause a reduced biceps reflex. Reflexes are preserved in MSK disorders and increased in CNS disorders.

3.  Sensory examination. The sensory examination involves testing of light touch, pain (pinprick), vibration, and joint position sensations in the upper and lower extremities. Particular attention is paid to cutaneous areas where there are sensory complaints.

4.  Maneuvers. Several maneuvers may aid in the evaluation of UE sensorimotor complaints. Tinel’s sign, originally described for assessment of regenerating nerve fibers, is now commonly employed to elicit paresthesias radiating in a nerve’s cutaneous distribution. It is elicited by gentle tapping over a nerve. It may be observed in association with regenerating nerve fibers, neuroma, focal demyelination, and even in normal individuals. Tinel’s sign is easier to elicit from a diseased nerve than from a normal nerve, and thus it may help to localize an abnormal nerve. It is commonly used to assess for CTS by tapping over the median nerve on the volar surface of the wrist. With Phalen’s maneuver, the wrist is flexed for up to 1 minute to elicit paresthesias in the median nerve distribution. A positive Phalen’s maneuver provides supportive evidence for CTS. Adson’s maneuver refers to assessing the radial pulse when the arm is abducted and extended. Loss of the radial pulse with this maneuver is alleged to indicate compression of the subclavian artery by a cervical rib or a hypertrophied scalenus muscle. However, it is not a useful test because it is subjective and may cause normal individuals to lose their radial pulse.

C.  Diagnostic studies.

1.  EDS consist of nerve conduction studies (NCS) and electromyography (EMG). These tests permit an objective and quantitative assessment of individual peripheral nerves and muscles. They can substantiate a clinically suspected diagnosis or reveal unsuspected abnormalities. With rare exceptions, all patients with symptoms of UE pain and sensorimotor symptoms should have EDS as part of the initial diagnostic evaluation. When performed in the first few days after onset of nerve injury, EDS do not reveal as many abnormalities as when performed 7 to 10 days later. However, performing EDS early after injury allows the opportunity to document preexisting abnormalities. This may be important for complicated diagnostic cases or when medicolegal issues occur. Detailed discussion of EDS is found in Chapter 36.

2.  Radiologic studies.

a.  Plain films. After head or neck trauma, cervical spine films are necessary to evaluate for fractures. When cervical radiculopathy is suspected, cervical spine films may reveal narrowing of specific neural foramina. Cervical spine films may also be useful in detecting a cervical rib, which should be investigated when clinical and EDS evidence suggests a neurogenic thoracic outlet syndrome (TOS). The patient with brachial plexopathy should have a chest film to evaluate for malignancy. If clinical evidence suggests Pancoast’s syndrome, apical chest film views should be included to search for an apical tumor. Plain films may also be useful in evaluation of MSK disorders, by revealing evidence of degenerative arthritis or tendon calcifications.

b.  Magnetic resonance imaging (MRI). Cervical spine MRI studies are usually performed to evaluate cervical radiculopathy. Myelography combined with computerized tomography may be used when MRI is not an option. MRI of the brachial plexus is often used to search for evidence of tumor as the cause of brachial plexopathy. MRI can also demonstrate enlargement or increased signal within the brachial plexus.

c.  Ultrasound can be used to evaluate focal peripheral nerve abnormalities. It has been particularly helpful for evaluating the median nerve at the wrist in patients with suspected CTS. The typical ultrasound finding in patients with CTS is enlargement of the median nerve cross-sectional area (CSA) at the wrist. Ultrasound can also demonstrate focal enlargement of other nerves, for example, ulnar nerve enlargement in the elbow region. Video 24.1 demonstrates ultrasound of the median nerve at the wrist in a normal individual. The CSA is measured by tracing the outline of the median nerve with the ultrasound machine. The upper limit of normal CSA for the median nerve at the wrist is 10 mm² (or 0.1 cm²).

3.  Laboratory studies for investigation of systemic illnesses are obtained for patients with UE sensorimotor complaints, depending on individual case circumstances. Tests that may be useful include complete blood count (CBC) with differential, chemistry panel, blood sugar, erythrocyte sedimentation rate, antinuclear antibody, urinalysis, serum immunofixation electrophoresis, thyroid function, and, occasionally, spinal fluid tests.

D.  Unexplained Symptoms. When thorough evaluation of UE pain or sensorimotor symptoms does not reveal a specific PNS or MSK disorder, alternative explanations must be considered. Possibilities include positional nerve compression, CNS disease, depression, psychological factors, or malingering. The symptoms and signs of CNS and PNS diseases may overlap, particularly for slowly progressive conditions—for example, brain tumor or multiple sclerosis. Clues suggesting CNS disease include painless weakness or sensory disturbance, upper motor neuron signs, altered consciousness or personality, or problems with cognition, language, or vision. Depression may present with unexplained UE pain or sensorimotor symptoms. Some patients may not have frank depression but unhappiness or conflict in the psychosocial realm, which manifests as neurologic symptoms. Often patients with this cause of symptoms are unable to identify a relationship between their psychological state and neurologic symptoms. Others have onset of symptoms after accidents or injuries, and either the process of litigation or the power of suggestion from inquisitive physicians distorts the usual concept of wellness and perpetuates the symptoms. Patients with unexplained symptoms should have neurologic consultation, and may need to be followed and observed over time.

DIAGNOSTIC APPROACH

The history provides initial hypotheses about the cause of the symptoms, and these hypotheses are tested during the physical examination. Knowledge of PNS anatomy is essential for interpreting UE sensorimotor symptoms and signs. In almost all cases, EDS are performed to help localize or exclude a suspected PNS disorder. When a PNS disorder is present, EDS help determine the severity and type of pathologic process. Additional diagnostic assessments may include radiologic studies or laboratory tests, depending on individual patient circumstances.

SELECTED DISORDERS AND CRITERIA FOR DIAGNOSIS

A.  PNS disorders.

1.  Mononeuropathy.

a.  Median nerve.

(1)  CTS

(a)  Anatomy and etiology. CTS is a very common disorder caused by compression of the median nerve at the wrist within the unyielding space known as the carpal tunnel. Many disorders compromise this space, resulting in median nerve compression. The most common cause is flexor tenosynovitis, which may be associated with excessive physical use of the hands. Patients with primary carpal stenosis—that is, a narrow carpal tunnel—may be especially prone to CTS. Other local factors causing CTS include vascular lesions, abnormal tendons, ganglion cysts, tumoral calcinosis, pseudoarthrosis, and infection. Systemic disorders associated with CTS include endocrine disorders such as hyperparathyroidism, acromegaly, and hypothyroidism, and rheumatologic disorders such as rheumatoid arthritis, systemic lupus erythematosus, polymyalgia rheumatica, temporal arteritis, scleroderma, and gout. Other conditions predisposing to CTS include diabetic and other polyneuropathies, chronic hemodialysis, shunts for hemodialysis, and pregnancy.

(b)  Clinical features of CTS include numbness or tingling involving one or more of the first four digits (thumb through ring finger), although occasionally the entire hand is involved. There may be pain in the fingers or wrist, and occasionally in the forearm or shoulder. Patients are often awakened at night by these symptoms, and physical activity with the hands may exacerbate symptoms. Advanced cases can develop weakness and atrophy of the thenar muscle. Physical examination reveals decreased sensation in the volar aspect of the first four digits. Because the median nerve innervation frequently supplies only the lateral half of the ring finger, sparing of sensation on the medial half of the ring finger is a helpful sign. CTS typically spares sensation over the thenar eminence. Advanced cases show weakness and atrophy of the abductor pollicis brevis. Tinel’s and Phalen’s signs may be present.

(c)  Diagnosis of CTS is established by clinical history, physical findings, and EDS. The EDS findings vary with the severity of the disorder. In mild cases, the amplitude of the median compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) are normal, and the wrist latency values are prolonged. The median NCS reveals focal slowing across the wrist. Slowing of NCS in proximal median nerve segments should not exclude the diagnosis of CTS. In some cases, there may be conduction block at the wrist level. In more advanced cases, the median CMAP and SNAP amplitude values are reduced, and fibrillation potentials may occur in the abductor pollicis brevis muscle. The ulnar nerve studies in the same hand are normal. Ultrasound can also be used to diagnose CTS. The typical ultrasound finding in patients with CTS is enlargement of the median nerve CSA at the wrist. Most studies indicate median nerve CSA at the wrist greater than 10 mm² is abnormal. Comparison of the wrist and forearm median nerve CSA is considered the most sensitive ultrasound measurement for CTS with a wrist-to-forearm ratio greater than 1.4 being abnormal. Additional ultrasound abnormalities in CTS include increased hypoechoic signal in the median nerve, disproportionate flattening of the median nerve, bowing of the flexor retinaculum, and reduced excursion of the median nerve with digit movement. Some patients with typical symptoms of CTS have normal EDS. Within this group of “EMG negative CTS patients,” some will have enlarged CSA by ultrasound. In patients with positive EDS studies, the degree of enlargement of median nerve CSA by ultrasound correlates with the severity of the EDS abnormalities. Some patients may have multiple entrapment neuropathies, such as bilateral median neuropathies at the wrist and bilateral ulnar neuropathies at the elbows. In this circumstance, it is necessary to evaluate lower extremity nerves for the possibility of an underlying polyneuropathy.

(2)  Pronator teres syndrome

(a)  Anatomy and etiology. The pronator teres syndrome refers to compression of the median nerve in the forearm where it passes between the heads of the pronator teres muscle. This uncommon disorder is usually related to an occupation involving repetitive pronation of the forearm, which leads to hypertrophy of the pronator teres muscle. Other causes include a fibrous band from pronator teres to flexor digitorum superficialis, or local trauma.

(b)  Clinical features. The predominant symptom is pain in the volar forearm. Median innervated muscles, including the pronator teres, remain strong. Median sensory function is typically normal. Examination may show tenderness in the region of the pronator teres muscle, and there may be a Tinel’s sign over the pronator muscle.

(c)  Diagnosis is established primarily by clinical features. EDS are often normal, but occasionally slow median NCS may be observed in the forearm segment.

(3)  Anterior interosseous syndrome

(a)  Anatomy and etiology. This relatively uncommon median nerve disorder involves compression of the anterior interosseous branch of the median nerve in the forearm, usually by a fibrous band from the pronator teres or the flexor digitorum superficialis muscles. Other forearm anomalies or forearm trauma may also cause the disorder. The anterior interosseous nerve (AIN) is a purely motor nerve that supplies the flexor pollicis longus (FPL), flexor digitorum (FD) I and II, and pronator quadratus muscles.

(b)  Clinical features include forearm or elbow pain combined with weakness of flexion of the distal phalanx of the thumb (FPL) and the index and middle fingers (FD). Patients note inability to pinch the thumb and index finger together. Pronation strength is preserved as the pronator teres muscle is unaffected.

(c)  Diagnosis is established by the abovementioned clinical features and EDS. The median NCS are normal. The EMG shows fibrillation potentials confined to one or more of the above muscles supplied by the AIN. When AIN causes weakness confined to the FPL, EMG is extremely helpful for differentiating a partial AIN syndrome from rupture of the FPL tendon.

b.  Ulnar nerve.

(1)  Cubital tunnel syndrome

(a)  Anatomy and etiology. The ulnar nerve may become compressed in the elbow region either in the condylar groove or the cubital tunnel. The cubital tunnel is formed on the sides by the two heads of the flexor carpi ulnaris muscle with a floor (medial ligament of the elbow), and roof (aponeurosis of the flexor carpi ulnaris muscle) completing the boundaries. The ulnar nerve runs through this space, and then underneath the flexor carpi ulnaris muscle. Remote elbow trauma, with or without fracture, predisposes to later development of entrapment neuropathy in the elbow region (tardy ulnar palsy). However, many patients develop ulnar neuropathy without antecedent trauma. Repetitive movement at the elbow or prolonged flexion of the elbow may be predisposing factors.

(b)  Clinical features include sensory complaints in the ulnar division of the hand (the fifth digit and the medial half of the fourth) and the ulnar-innervated portion of the hand and wrist. Sensory complaints may include decreased sensation, paresthesias, and pain. Pain may involve the medial forearm and elbow. Weakness involves the interossei, abductor digiti minimi, adductor pollicis, and flexor pollicis brevis. When weakness is chronic, atrophy may occur, and a claw hand deformity may develop. Most often, the flexor carpi ulnaris muscle remains strong. A diagnosis of ulnar neuropathy requires normal strength in C8–T1 muscles innervated by the median and radial nerves.

(c)  Diagnosis is established by the characteristic history and physical findings, and EDS. Ulnar neuropathy at the elbow may show reduction of the ulnar CMAP and SNAP. There may be evidence of conduction block in motor fibers that can be localized to the elbow region. Ulnar NCS may be focally slow across the elbow. The EMG may show fibrillation potentials and/or abnormal motor unit potentials (MUPs) in ulnar-innervated hand muscles. Usually the flexor carpi ulnaris does not show fibrillation potentials, although it may if its motor branch is also compressed.

(2)  Compression at the wrist (Guyon’s canal)

(a)  Anatomy and etiology. Guyon’s canal is a fibro-osseous tunnel connecting the pisiform and hamate wrist bones through which the ulnar nerve travels. As the ulnar nerve emerges from Guyon’s canal, it divides into motor and sensory branches. The deep terminal branch is purely motor and supplies all of the ulnar-innervated hand muscles. The superficial terminal branch supplies sensation to the medial distal half of the palm and the palmar surfaces of the fourth and fifth digits. Sensation to the medial proximal half of the palm is supplied by the palmar cutaneous branch of the ulnar nerve, which arises in the mid-forearm and does not pass through Guyon’s canal. Sensation to the medial dorsal half of the hand is supplied by the dorsal cutaneous branch of the ulnar nerve, which arises above the wrist and does not pass through Guyon’s canal. Factors predisposing to ulnar neuropathy at the wrist include chronic compression, which may occur in cyclists and local trauma—for example, wrist fracture.

(b)  Clinical features vary depending on the precise level of abnormality. Compression of the entire ulnar nerve within Guyon’s canal or of the two branches as they leave the canal causes weakness of all ulnar-innervated hand muscles and sensory loss in the superficial terminal branch distribution. Sensation of the dorsal medial hand and the proximal half of the medial palm is spared because sensation is supplied by other branches. Compression of the deep terminal motor branch may occur in isolation either before or after it supplies the hypothenar muscles, producing ulnar-innervated hand muscle weakness with no sensory loss. Finally, compression of only the superficial terminal branch causes sensory loss in its palmar distribution with normal hand strength.

(c)  Diagnosis is established by clinical examination and EDS. The EDS findings vary depending on which of the abovementioned ulnar nerve branches is involved. If the superficial terminal sensory branch is involved, NCS will show a reduced or absent ulnar SNAP recorded from the fifth digit, but the SNAP from the dorsal ulnar cutaneous nerve remains normal. If the abnormality involves the deep terminal branch, ulnar CMAP amplitude may be reduced and there may be fibrillation potentials or abnormal MUPs in ulnar-innervated hand muscles.

c.  Radial nerve.

(1)  Axilla or spiral groove compression

(a)  Anatomy and etiology. The radial nerve may be compressed against the humerus by external pressure in the axilla or the spiral groove. Compression in the axilla can be caused by improper use of crutches. Compression in the spiral groove is likely to occur when an individual falls asleep with the arm hanging over a chair, or with a partner’s head against the arm. Radial nerve compression is especially likely if use of alcohol or sedatives prevents the patient from normal turning during sleep. The term “Saturday night palsy” has been used for such a radial nerve palsy. A similar outcome may follow use of an arm tourniquet during surgery. The radial nerve may also be injured in the spiral groove by blunt trauma, fractures of the humerus, and rarely by vigorous arm exercise.

(b)  Clinical features are weakness of radial-innervated muscles and sensory loss on the dorsal aspects of the hand, thumb, and index and middle fingers. Radial-innervated muscles include triceps, brachioradialis, supinator, and the wrist and finger extensors. The triceps is affected by radial nerve compression in the axilla but spared with spiral groove compression. Weakness of wrist extensors causes wrist drop. Inability to stabilize the wrist prevents normal hand interossei muscle function giving the false impression that ulnar-innervated hand muscles are weak.

(c)  Diagnosis of radial mononeuropathy is confirmed by clinical features and EDS. Nerve conduction studies show a reduced-amplitude radial CMAP and reduced or absent SNAP. The presence or absence of fibrillation potentials in triceps helps to localize the compression site (axilla or spiral groove).

(2)  PIN

(a)  Anatomy and etiology. The PIN is the purely motor termination of the radial nerve in the forearm. The PIN supplies the supinator muscle and the wrist and finger extensors. Entrapment of the PIN is relatively uncommon. When this occurs, it is usually at the level of the supinator muscle. Predisposing factors include vigorous use of the arm, fracture of the head of the radius, and other local traumas. Hypertrophied synovia of the elbow joint in patients with rheumatoid arthritis may compress the PIN.

(b)  Clinical features are weakness of the wrist and finger extensors. Some patients have pain in the elbow or dorsal forearm. There are no sensory abnormalities apart from pain, because the PIN is purely motor.

(c)  Diagnosis is established by the abovementioned clinical features and EDS. NCS show a reduced-amplitude radial CMAP and normal radial SNAP. The EMG exam shows fibrillation potentials and abnormal MUPs in the aforementioned radial-innervated muscles.

(3)  The superficial sensory branch

(a)  Anatomy and etiology. The superficial sensory branch of the radial nerve arises in the vicinity of the elbow and supplies sensation to the dorsolateral hand and the dorsal aspects of the first three digits. It may be injured at the wrist level by local trauma or compression from tight objects around the wrist, such as watchbands or handcuffs.

(b)  Clinical features are purely sensory, with paresthesias and sensory loss in the radial sensory distribution.

(c)  Diagnosis is made by the history, physical findings, and NCS evidence of a reduced or absent superficial radial SNAP.

d.  Axillary nerve.

(1)  Anatomy and etiology. The posterior cord of the brachial plexus divides into the radial and axillary nerves. The axillary nerve travels below the shoulder joint and supplies the teres minor muscle, which externally rotates the arm. The axillary nerve then courses behind and lateral to the humerus before dividing into anterior and posterior branches, which supply corresponding portions of the deltoid muscle. The posterior branch gives a cutaneous nerve that supplies the skin over the lateral deltoid. The axillary nerve may be injured by shoulder dislocation or fractures of the humerus. It may be the only nerve affected by idiopathic brachial plexopathy (see Section A.2.a under Selected Disorders and Criteria for Diagnosis).

(2)  Clinical features. The main clinical manifestation is impaired shoulder abduction resulting from deltoid weakness. The supraspinatus initiates arm abduction, so patients may retain limited arm abduction. Weakness of the teres minor muscle may be difficult to demonstrate on physical examination because of normal infraspinatus muscle function. Sensory loss may be demonstrated over the lateral portion of the deltoid muscle.

(3)  Diagnosis is confirmed by weakness limited to the deltoid muscle and EMG abnormalities restricted to the deltoid and teres minor muscles. An axillary NCS study with surface recording from the deltoid muscle may show delay or reduced amplitude of the axillary nerve CMAP.

e.  Musculocutaneous nerve.

(1)  Anatomy and etiology. The musculocutaneous nerve arises from the lateral cord of the brachial plexus and supplies the coracobrachialis, biceps, and brachialis muscles. It continues in the forearm as the purely sensory lateral antebrachial cutaneous nerve. Mononeuropathy of the musculocutaneous nerve is uncommon, but it may occur with shoulder dislocation, direct trauma or compression, or sudden extension of the forearm.

(2)  Clinical features include impaired arm flexion resulting from weakness of the biceps and the other musculocutaneous-innervated muscles. The biceps reflex may be normal or reduced, depending on the severity of the biceps weakness. Sensory loss is present over the lateral forearm.

(3)  Diagnosis. The clinical features of musculocutaneous neuropathy closely parallel those of C5 radiculopathy. Diagnosis is established by the abovementioned clinical features and EDS results that differentiate C5 radiculopathy from musculocutaneous nerve mononeuropathy. The lateral antebrachial SNAP is reduced or absent in musculocutaneous neuropathy but normal in C5 radiculopathy. EMG shows involvement of only muscles supplied by the musculocutaneous nerve.

f.  Long thoracic nerve.

(1)  Anatomy and etiology. The long thoracic nerve is a purely motor nerve arising from the ventral rami of the C5, C6, and C7 spinal nerves. It courses along with other brachial plexus components underneath the clavicle, and then travels down the chest wall anterolaterally to supply the serratus anterior muscle. This large muscle fixes the scapula to the chest wall, providing general stability for the shoulder during arm movements. Injury of the long thoracic nerve may occur with trauma or with vigorous physical activities involving shoulder girdle movements. Long thoracic neuropathy may be caused by idiopathic brachial plexopathy.

(2)  Clinical features of long thoracic mononeuropathy include pain and weakness in the shoulder. Patients have difficulty abducting the arm or raising it above the head. Winging of the scapula is demonstrated by having the patient extend the arms forward and push against a wall. The scapula elevates from the chest wall because the weak serratus muscle cannot hold it.

(3)  Diagnosis is established by the abovementioned clinical features and EMG showing fibrillation potentials involving only the serratus anterior muscle. Long thoracic nerve NCS are technically difficult and other NCS are normal.

g.  Suprascapular nerve.

(1)  Anatomy and etiology. The suprascapular nerve is a purely motor nerve arising from the upper trunk of the brachial plexus and passing through the suprascapular notch on the upper border of the scapula to supply the supraspinatus and infraspinatus muscles. The suprascapular nerve is most often injured by trauma in which there is excessive forward flexion of the shoulder. It may be involved in idiopathic brachial plexopathy.

(2)  Clinical features are pain in the posterior shoulder and weakness of the spinati muscles. The supraspinatus initiates arm abduction, whereas the infraspinatus externally rotates the arm.

(3)  Diagnosis is established by clinical history, physical findings, and EDS. Routine NCS are normal, but motor NCS with recording from the supraspinatus muscle may show reduced amplitude or prolonged latency relative to the unaffected side. The EMG exam shows abnormalities confined to the spinati muscles on the affected side.

h.  Dorsal scapular nerve.

(1)  Anatomy and etiology. The DSN is a purely motor nerve arising from the upper trunk of the brachial plexus and passing through the scalenus medius muscle to supply the rhomboid and levator scapulae muscles. Injury to the DSN is uncommon.

(2)  Clinical features include pain in the scapular region and weakness of the rhomboid and levator scapulae muscles.

(3)  Diagnosis is established by clinical features and EMG showing fibrillation potentials restricted to the muscles supplied by the DSN. There is no satisfactory NCS for the DSN.

2.  Brachial plexopathy.

a.  Idiopathic brachial plexopathy.

(1)  Anatomy and etiology. Idiopathic brachial plexopathy, also known as Parsonage–Turner syndrome or neuralgic amyotrophy, is an uncommon condition believed to represent an immune-mediated neuropathy affecting various portions of the brachial plexus. An antecedent event such as an upper respiratory infection or immunization is present in about half of the cases.

(2)  Clinical features. The main clinical features are abrupt onset of severe pain in the shoulder and proximal arm followed at a variable interval (hours to weeks) by shoulder and arm muscle weakness. The pain is exacerbated by movement of the arm, shoulder, or neck, which may give the false impression of an MSK disorder. Any combination of muscles innervated by nerves arising from the brachial plexus may be involved, but there is a predilection for proximal muscles. Muscles supplied by the axillary, suprascapular, long thoracic, radial, musculocutaneous, and AINs are commonly involved. The nerve involvement may be extensive or restricted to a single nerve. Asymmetric contralateral involvement occurs in one-third of patients. Sensory loss or paresthesias may be present, but these features are relatively minor.

(3)  Diagnosis is established by the characteristic clinical history, physical findings, and EDS. Patients with this disorder typically present early for evaluation and treatment of the severe pain. If EDS are performed early, abnormalities of MUP recruitment may be observed, but the studies may be otherwise normal. If EDS are repeated 7 to 10 days after weakness begins, the NCS show evidence of axonal injury, with the distribution varying according to the specific nerves involved. EMG shows fibrillation potentials in clinically weak muscles, and often in muscles that were not judged weak by physical examination. For this reason, EMG is essential for determining the extent of injury.

b.  Neurogenic TOS.

(1)  Anatomy and etiology. The “true” neurogenic TOS is a very rare disorder in which the lower trunk of the brachial plexus is compressed by an elongated transverse process of C7, a rudimentary cervical rib, or a fibrous band running from either of these to the first rib.

(2)  Clinical features are weakness and wasting of the intrinsic hand muscles, most markedly affecting the abductor pollicis brevis muscle; pain involving the medial forearm or hand; and sensory loss involving the fourth and fifth fingers and the medial hand and distal forearm.

(3)  Diagnosis is established by clinical features and characteristic EDS results. Radiographic evidence of an elongated C7 transverse process or a rudimentary cervical rib is helpful but not mandatory for diagnosis, because the structural problem may be a fibrous band that cannot be detected on imaging studies. The nerve conduction findings include severely reduced or absent median CMAP, normal median SNAP, reduced or absent ulnar SNAP, and mildly reduced or normal ulnar CMAP. The EMG exam shows fibrillation potentials in lower trunk–innervated muscles, particularly those supplied by the median and ulnar nerves. In contrast to the rare and well-defined true neurogenic TOS is a condition commonly misdiagnosed as TOS, which has various UE sensorimotor symptoms but no consistent clinical history. Patients said to have this form of TOS have no objective neurologic abnormalities and no abnormalities on EDS. This form of TOS has been aptly referred to as “disputed” neurogenic TOS and its existence as an entity remains controversial. Patients erroneously diagnosed with this type of TOS are often subjected to first-rib resection, and, unfortunately, severe brachial plexopathy may be a complication.

c.  Brachial plexopathy in patients with malignancy.

(1)  Anatomy and etiology. Metastasis to the brachial plexus needs to be considered whenever a patient with a history of malignancy (especially breast or lung cancer) develops UE pain or sensorimotor symptoms. Brachial plexopathy is usually not the presenting feature of malignancy, except in Pancoast’s syndrome, in which an apical lung carcinoma invades the lower trunk of the brachial plexus. For patients who have undergone prior chest wall radiotherapy, brachial plexopathy from radiation injury may occur as a later complication.

(2)  Clinical features of brachial plexopathy resulting from tumor invasion are pain, weakness, and sensory changes that more commonly affect the lower plexus. Unlike idiopathic brachial plexopathy, malignant brachial plexopathy has a gradual onset of symptoms, and lymphedema of the arm is common. In Pancoast’s syndrome, patients usually first have pain in the medial arm, and may develop sensorimotor abnormalities in the lower trunk distribution. Horner’s syndrome (ipsilateral ptosis, miosis, and facial anhidrosis) often results from a tumor invading the inferior cervical sympathetic ganglion. Malignant plexopathy is more likely than radiation plexopathy to be painful and involve the lower trunk.

(3)  Diagnosis. A patient with a history of malignancy and new onset UE sensorimotor symptoms or pain should have EDS to exclude common conditions such as mononeuropathy or radiculopathy, which might cause symptoms identical to those of brachial plexopathy. The EDS can determine if there is evidence of brachial plexopathy and clarify the locations of abnormalities within the plexus. This information can help in planning and interpreting MRI studies of the plexus, which should be performed to look for evidence of tumor. Patients with lower trunk plexopathy should have apical chest film views to look for an apical lung tumor. Myokymic discharges detected by EDS in patients with prior chest wall radiotherapy support a diagnosis of radiation plexopathy but do not conclusively exclude tumor metastases.

3.  Cervical radiculopathy. The clinical and electrodiagnostic features of cervical radiculopathy are mentioned above, and thoroughly reviewed in Chapter 22.

B.  MSK disorders share in common the predominant symptom of pain and an absence of other neurologic manifestations. In general, EDS are normal when MSK disorders are the cause of UE pain symptoms. However, it is common for an underlying neurologic disorder affecting the PNS to result in a secondary MSK disorder, in which case EDS may be abnormal as a result of the underlying neurologic disorder.

1.  Rotator cuff injury. The rotator cuff comprises the tendons of the supraspinatus, infraspinatus, teres minor, and subscapularis muscles, which fix the humeral head in the glenoid fossa during shoulder abduction and provide internal and external arm rotation. Rotator cuff inflammation (tendinitis) and tear are common causes of shoulder pain. Tendinitis results from repetitive minor trauma to the cuff, and tear may occur as a chronic stage of this degenerative process, or acutely from abrupt trauma. With tendinitis or tear, there is shoulder pain on arm abduction or on internal or external arm rotation. With tear, there may be weakness of rotator cuff functions, but EMG studies are negative. Plain films may reveal tendon or subacromial bursa calcifications. Ultrasound or an arthrogram of the shoulder may confirm a rotator cuff tear.

2.  Bicipital tendinitis. Inflammation of the biceps tendon causes pain and tenderness in the anterior shoulder region. The pain may be reproduced by supination of the forearm against resistance or by flexion and extension of the shoulder. There are no neurologic abnormalities, and the diagnosis is established clinically.

3.  Adhesive capsulitis (frozen shoulder). Loss of motion at the shoulder joint may result in adhesion of the joint capsule to the humerus. Shoulder pain from any cause can lead to immobility and subsequent adhesive capsulitis. Alternatively, weakness of shoulder girdle muscles from either PNS or CNS disorders may cause this problem. Whatever the cause, the joint becomes stiff, and attempted motion causes severe shoulder pain. Muscle atrophy may result from PNS disease, or secondarily from disuse. The diagnosis is usually made by the clinical features.

4.  Lateral epicondylitis (tennis elbow). Overuse of the extensor carpi radialis muscles (wrist extensors), or direct trauma to their tendinous insertion on the lateral epicondyle, may lead to inflammation, degeneration, or tear of the tendons. This produces pain localized over the lateral epicondyle, which may be exacerbated by use of the forearm-wrist extensor muscles.

REFERRAL

Patients should be referred to a reliable EMG laboratory for EDS, as these studies facilitate accurate diagnosis. Establishing the diagnosis guides subsequent diagnostic testing and treatment decisions. In addition, EDS can estimate the severity of the abnormality, which can help to estimate prognosis. Neurologic consultation for UE pain or sensorimotor symptoms is appropriate at any stage of the evaluation process if there are questions concerning diagnosis or management.

Related posts:

Approach to the Patient with Gait Disturbances and Recurrent Falls Approach to the Patient with Acute Sensory Loss Multiple Sclerosis Approach to the Patient with Sleep Disorders Approach to the Patient with Chronic and Recurrent Headache Neuroimaging of Common Neurologic Conditions

Stay updated, free articles. Join our Telegram channel

Join