INTRODUCTION — Peripheral nerve damage affecting the upper extremities can vary widely in cause and extent. Many disorders, ranging from mild carpal tunnel syndrome to severe brachial plexopathy, need to be considered in a patient presenting with pain, sensory loss, or weakness involving the shoulder, arm, or hand. Causes and specific sites of peripheral nerve impairments affecting the upper extremity will be reviewed here.
Peripheral nerve syndromes involving the lower extremities are discussed separately. (See "Overview of lower extremity peripheral nerve syndromes".)
ANATOMY — Nerve roots emerge from the spinal cord from the C2 level and below, each exiting through its own individual foramen. The C2 through C4 roots merge close to the spinal column into a conglomeration known as the cervical plexus. Nerves emerging from this group include the phrenic and greater auricular. Although generally uninvolved in neurologic disease, lesions can occasionally affect this region and cause head extensor weakness or diaphragm paralysis.
The C5 through T1 roots also emerge from the spinal column and give off small branches proximally that contribute to form the long thoracic nerve, which innervates the serratus anterior muscle. The roots then merge in a complex region known as the brachial plexus. A number of regions within the plexus have been defined by anatomists, including trunks, divisions, cords, branches, and proximal nerve; however, for practical purposes an understanding of the individual trunks, cords, and nerves is all that is necessary to correctly classify a problem affecting this region (figure 1):
●The C5 and C6 roots merge to form the upper trunk; the C7 root alone makes up the middle trunk; the C8 and T1 roots form the lower trunk.
●The upper trunk becomes the lateral cord after giving off branches that contribute to the posterior cord; the lower trunk becomes the medial cord after giving off branches that contribute to the posterior cord; the middle trunk becomes the posterior cord after giving off branches that contribute to the lateral cord.
●A number of nerves emerge from the lateral region of the plexus, including, from proximal to distal, the dorsal scapular nerve, the suprascapular nerve, the musculocutaneous nerve, and, in part, the median nerve. The ulnar nerve is the major nerve from the medial region of the plexus, while the posterior cord gives off a number of significant nerves including the axillary, subscapular, thoracodorsal, and, most importantly, the radial nerve.
●As the major nerves descend down the arm, the radial and median give off two important branches, the posterior and anterior interosseous nerves, respectively. All of the nerves give off multiple branches even more distally, although most are not clinically relevant except in very specific situations. These smaller branches will be discussed where clinically distinct syndromes exist.
ETIOLOGIES — A number of different processes may affect normal nerve function in a focal fashion, as compared with a disorder such as polyneuropathy in which more diffuse neuronal dysfunction occurs. (See "Overview of polyneuropathy".)
Compression — Compression of nerve segments (including neurapraxia and axonotmesis) is the most common problem that affects neuronal structures in the upper extremity. Compression can affect distal nerve segments, usually related to entrapment as a nerve courses through a ligamentous canal (eg, median nerve in the carpal tunnel, suprascapular nerve at the superior scapular notch), but may also occur very proximally at the root level (eg, when a herniated cervical disc compresses the spinal root).
The pathologic processes at any site of entrapment are relatively similar. A degree of direct compression against the nerve with associated nerve ischemia plays a role.
●In its mildest form, the problem may be intermittent due to positioning; a common situation is that of paresthesias in the hand in a patient with carpal tunnel syndrome when the wrist is flexed, most likely secondary to temporary nerve ischemia.
●Demyelination occurs as compression becomes more consistent and chronic. Symptoms are usually persistent at this point, although often are worsened with certain movement or positions. Pain and weakness, generally minimally noticeable early on, now may become more prominent.
●Distal nerve segments will no longer function as compression progresses and Wallerian degeneration occurs. In severe cases, the entire distal segment of nerve can degenerate, similar to what would be seen in a nerve transection. (See 'Transection' below.)
From a physiologic standpoint, the patient will remain asymptomatic as long as all nerve impulses are transmitted through a region of compression. As ischemia or demyelination occurs, nerve conduction will first be slowed, and then eventually blocked completely. Slowing of nerve conduction has minimal physiologic correlate; only complete conduction block of neuronal impulses produces functional sensory loss or weakness. Conduction block of more and more nerve fibers occurs as compression worsens. Eventually almost no impulses make it through the compressed area, while distal neuronal degeneration simultaneously begins to take place.
Transection — Acute nerve transection (neurotmesis) is much less common than chronic nerve compression. It can occur with severe trauma to the arm (eg, a knife wound) as the distal nerve is completely separated from the proximal portion. Unlike even severe cases of nerve compression, the basement membrane of each individual nerve cell no longer remains intact following transection; without intervention (ie, surgical reattachment), regrowth of the nerve is impossible. Complete loss of sensory and motor responses occurs.
Nerve ischemia/infarct — Nerve infarction typically only occurs with vasculitis and atherosclerotic disease. Nerve infarction in patients with vasculitis causes an axonal injury pattern, typically at specific regions. Certain nerves tend to be most affected in the upper extremity: the median nerve in the upper arm and ulnar nerve just proximal to the elbow segment. (See "Clinical manifestations and diagnosis of vasculitic neuropathies".)
Unlike the case of compressive neuropathy, conduction velocity slowing does not occur. The entire distal segment of the nerve degenerates within a few days of focal nerve infarction. However, since the basement membrane remains intact, regrowth of the nerve may occur with control of the underlying disease. Severe atherosclerotic disease can occasionally produce similar findings.
Radiation-induced injury — Radiation therapy that includes the brachial plexus in the treatment field can result in a transient, acute brachial plexopathy that is self-limited. Symptoms include numbness in the thumb and first finger of the affected side, and weakness in the shoulder and biceps muscle.
Brachial plexus irradiation also can cause a more serious late-delayed brachial plexopathy, manifested by paresthesia, hypesthesia, weakness, and impaired reflexes, with symptoms progressing to chronic pain and progressive arm paralysis. This entity occurs after a variable latent period that can span many years and is generally irreversible. The primary diagnostic difficulty is distinguishing radiation-induced, late-delayed brachial plexopathy from recurrent tumor. (See "Brachial plexus syndromes", section on 'Neoplastic and radiation-induced brachial plexopathy'.)
Inflammation — Inflammatory processes of the nerve or roots also can cause significant problems affecting the arm. Infectious disorders such as herpes simplex, Epstein-Barr virus, and most commonly herpes zoster virus can produce syndromes of sensory loss and motor dysfunction. An idiopathic inflammatory response is also responsible for the syndrome of brachial neuritis (neuralgic amyotrophy).
Degeneration — Focal degeneration of neurons may occur in certain disorders. Most concerning is Hirayama disease, which is a focal form of motor neuron cell loss associated with progressive weakness of one or both upper limbs over a period of months. It may also be an early manifestation of amyotrophic lateral sclerosis. (See "Diagnosis of amyotrophic lateral sclerosis and other forms of motor neuron disease", section on 'Monomelic amyotrophy'.)
Metabolic — Metabolic problems generally do not produce focal nerve lesions, except indirectly as can occur in patients with diabetes mellitus or hypothyroidism. Compression neuropathies (such as carpal tunnel syndrome) are much more common in these disorders for unclear reasons.
Occasionally, diabetes mellitus has also been associated with a vasculitic-like picture (diabetic mononeuropathy multiplex). (See "Epidemiology and classification of diabetic neuropathy".)
EPIDEMIOLOGY — Carpal tunnel syndrome is the most common mononeuropathy, although the prevalence varies with the population studied. In one population-based study in the Netherlands, clinical carpal tunnel syndrome was present in 3.4 percent of all people, and was likely present, although undiagnosed, in an additional 5.8 percent . The disorder was much more common in females; the overall prevalence was only 0.6 percent in men. In another study from the Mayo Clinic, the annual incidence rate was only 99 per 100,000 (0.1 percent) with a female-to-male ratio of 3:1 .
Cervical radiculopathy is also common. At the Mayo Clinic, the average incidence of this disorder between 1976 and 1990 was 83 per 100,000, with higher rates in males than females . The incidence was highest in people 50 to 54 years of age, with C6 and C7 root lesions making up 64 percent of all cases.
The incidence of brachial plexitis has also been studied through the Mayo Clinic records. Over a 12-year period, the annual incidence of this disorder was only 1.6 per 100,000 population .
It is likely that these numbers are underestimations of the true incidence. Mild cases of radiculopathy or brachial neuritis may never reach medical attention or may be misdiagnosed as a musculoskeletal injury.
OVERVIEW OF DIAGNOSTIC TESTING
Electrodiagnostic studies — Electromyography (EMG) and nerve conduction studies (NCS) remain the most effective means of identifying and classifying a disorder affecting the upper extremity. (See "Overview of electromyography" and "Overview of nerve conduction studies".)
Focal entrapments of the median, radial, or ulnar nerves are generally straightforward to determine using EMG/NCS. The electromyographer looks for evidence of demyelination (conduction velocity slowing and conduction block) across likely affected segments of nerve, such as the median nerve at the wrist in carpal tunnel syndrome. Similar findings may be found across the elbow segment in ulnar neuropathy and across the spiral groove in radial neuropathy. EMG tends to be mainly confirmatory and will give some insight into lesion severity.
In plexopathies, abnormalities are usually found in several nerves emanating from one region of the plexus, such as the upper trunk. Studying conduction across the plexus is generally not performed for technical reasons; thus, the usual findings of demyelination cannot be sought. Instead, testing is confined to distal segments and a search for axon loss is pursued. As an example, in a patient with an upper trunk lesion, reductions in the amplitude of the median, radial, and musculocutaneous sensory responses are typical. Since both standard median and ulnar motor testing are confined to lower trunk muscles, these studies are usually normal. However, on needle EMG, muscles innervated by upper trunk fibers can be studied; in these, fibrillation potentials, positive sharp waves, and chronic reinnervation may be identified. In lower trunk problems, ulnar and medial antebrachial cutaneous sensory responses are reduced while ulnar and median motor studies can both show abnormalities. On EMG, evidence of denervation and chronic reinnervation may be found in C8 to T1 muscles.
In radiculopathy, sensory responses are spared since the lesion is proximal to the dorsal root ganglion. Motor studies are usually also normal, unless the C8 to T1 roots are affected. Abnormalities typically are identified only on needle examination and affect the muscles derived from the involved roots.
Imaging — Imaging is the best first study to obtain in some patients. As an example, magnetic resonance imaging (MRI) of the cervical spine is probably the best first test in a patient with radiating neck pain, sensory loss over digits 2 to 4, and weakness in C7 muscles. However, in some situations, a patient's complaints are more nondescript. Pain may be nonfocal, weakness minimally present, and no fixed sensory loss identified. In these situations, EMG is probably the first test to pursue and, depending upon the results, imaging of the appropriate area can be performed subsequently if needed. In one study, although imaging with MRI was found to be in agreement with EMG findings in 60 percent of cases, it provided different information in 40 percent, suggesting that the two modalities often provide complementary information .
The utility of plain films generally is limited, with a few exceptions.
●Cervical spine films with extension and flexion may be helpful in sorting out cervical instability and will give a sense of the degree of degeneration. Loss of disc space at one level may suggest a herniated nucleus pulposus. Straightening of the normal cervical lordosis may suggest paraspinal muscle spasm. Osteolytic lesions can be identified.
●Chest x-ray may be helpful in determining the cause of a lower trunk plexopathy when lesions in the apex of the lung are responsible. The presence or absence of a cervical rib also can be determined. (See "Brachial plexus syndromes".)
●Plain films of the distal arm are rarely indicated, except in cases of trauma or when a palpable mass lesion is present.
MRI can be valuable in diagnosis. In cervical spine disease, specifics of disc herniation, degeneration, and degree of compression of a certain root have made this tool very helpful, especially when considering a surgical option. In patients with idiopathic plexopathies, one-time imaging, via MR neurography , is warranted as well to exclude the possibility of a mass lesion in the region. MRI of peripheral nerves is occasionally performed but has generally taken a reduced role as ultrasound has become increasingly utilized.
Ultrasound is now being employed as an important ancillary tool in the assessment of many upper extremity neurologic disorders. High-resolution ultrasound is particularly informative with respect to nerve compression syndromes, such as carpal tunnel syndrome, and focal enlargement of the nerve appears to be a robust indicator of local pathology. Ultrasound may be useful for the study of inflammatory and traumatic neuropathies and can identify neoplastic changes in nerves as well. It can be useful to assess any unusual mononeuropathy to help assess for mass or localized compressed. (See "Diagnostic ultrasound in neuromuscular disease", section on 'Findings in neuropathy'.)
Computed tomography (CT) is relatively rarely used but does have value in cervical spine assessment in patients with non-MRI-compatible implanted devices. CT also provides helpful information regarding osseous structures.
Laboratory testing — Serologic testing is usually of limited value in patients presenting with focal symptoms affecting the arm. However, some tests are worth considering:
●Thyroid function tests in patients with carpal tunnel syndrome
●Fasting glucose and hemoglobin A1C in patients with carpal tunnel syndrome, especially if a mild polyneuropathy may also be present
●Lyme titers in patients with polyradiculopathy, especially in endemic areas
●Hereditary neuropathy with predisposition to pressure palsy gene test in patients with multiple mononeuropathies (affecting at least two extremities)
In patients with mononeuropathy multiplex, many other laboratory studies are warranted in an attempt to identify the underlying disorder. (See "Treatment and prognosis of nonsystemic vasculitic neuropathy".)
Lumbar puncture — Lumbar puncture is warranted in patients with unusual presentations of radiculopathy. The cerebrospinal fluid (CSF) should be examined for evidence of inflammation (including elevated CSF protein and mononuclear cells) and serologic testing for Lyme disease and syphilis.
MEDIAN NERVE SYNDROMES
Carpal tunnel syndrome — The carpal tunnel is formed by the transverse carpal ligament (flexor retinaculum) superiorly and the carpal bones inferiorly (figure 2). The median nerve, accompanied by the nine flexor tendons of the forearm musculature, must pass through this anatomic tunnel (figure 3). The pathophysiology of carpal tunnel syndrome is multifactorial. Increased pressure in the intracarpal canal is thought to play a key role in the development of clinical carpal tunnel syndrome. (See "Carpal tunnel syndrome: Pathophysiology and risk factors".)
Carpal tunnel syndrome is the most common upper extremity mononeuropathy. Symptoms usually include painful paresthesias in a distribution that includes the median nerve territory, with involvement of the first three digits and the radial half of the fourth digit (figure 4). The symptoms are typically worse at night and characteristically awaken affected patients from sleep. However, there is a wide range of variability. The pain and paresthesia may be localized to the wrist or involve the entire hand. It is not uncommon for sensory symptoms to radiate proximally into the forearm, and less frequently to radiate above the elbow to the shoulder. Fixed sensory loss and weakness may develop as entrapment of the median nerve grows more severe. (See "Carpal tunnel syndrome: Clinical manifestations and diagnosis".)
Treatment of carpal tunnel syndrome consists of conservative therapy with wrist splinting, especially at night or while performing activities that exacerbate symptoms. If this fails, steroid injection into the wrist is often helpful in relieving symptoms (at least temporarily in a majority of cases). Surgical release of the flexor retinaculum is indicated for patients with persistent symptoms that do not respond to conservative therapy; results are usually excellent. (See "Carpal tunnel syndrome: Treatment and prognosis".)
Pronator teres syndrome — Entrapment of the median nerve occasionally occurs in the proximal forearm at the site where the nerve passes through the pronator teres muscle. This syndrome generally occurs in physically active people, such as professional bicycle riders, and is rare. Patients may present with forearm pain and sensory loss involving the entire lateral palm. Sensory loss over the thenar eminence is also typical, differentiating this disorder from carpal tunnel syndrome, in which sensation in that area is spared.
Electrophysiologic testing reveals slowed conduction velocity in the forearm and, in severe cases, conduction block. Needle examination may demonstrate abnormalities in median innervated forearm muscles, including the flexor carpi radialis.
Treatment of the pronator teres syndrome usually requires a reduction in the symptom promoting activity. Nonsteroidal antiinflammatory drugs may provide some pain relief; injection into the tender sites of the pronator teres muscle with a corticosteroid and local anesthetic agent (10 to 20 mg of methylprednisolone acetate, and 1 mL of 1 percent lidocaine hydrochloride using a #23 or #25 needle) is useful if pain continues. Surgery aimed at decompressing the nerve within the pronator teres muscle is helpful if the disability persists for several months despite these measures.
Anterior interosseous neuropathy — 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). (See 'Brachial plexopathy' below.)
Other disorders — More proximal median nerve compression rarely can occur in the region just above the elbow in some adults who have a small band attached to the distal humerus (the ligament of Struthers). The median nerve is most prone to infarction in a similar region just proximal to the elbow in patients with a vasculitic process. In both of these disorders, the clinical finding of weakness in multiple median and anterior interosseous innervated muscles is helpful. Electrophysiologically, fibrillation potentials and positive waves may also be identified in these muscles. Sensory loss remains confined to the lateral aspect of the hand.
ULNAR NERVE SYNDROMES
Ulnar neuropathy at the elbow and wrist — Ulnar neuropathy at the elbow and wrist is reviewed here briefly and discussed in detail elsewhere. (See "Ulnar neuropathy at the elbow and wrist".)
Ulnar neuropathy at the elbow (figure 5) is the second most common compression neuropathy affecting the upper extremities. In mild cases, symptoms include sensory loss and paresthesias over digits 4 and 5 (figure 6). In more severe cases, weakness of the interosseous muscles of the hand becomes apparent and the patient may complain of worsened grip and clumsiness. Pain in the region of the elbow also is common, although not universal. Involvement of ulnar-innervated forearm muscles leads to weakness in finger and wrist flexion. (See "Ulnar neuropathy at the elbow and wrist", section on 'Clinical features' and "Ulnar neuropathy at the elbow and wrist", section on 'Ulnar neuropathy at the elbow'.)
Compression of the ulnar nerve occasionally occurs in the wrist (figure 7). Like the median nerve, the ulnar nerve travels through its own tunnel into the wrist, known as Guyon's canal. Compression of the nerve can occur in the canal itself or distal, in the proximal hand. Compression at the wrist may appear clinically similar to that at the elbow: weakness in the interossei muscles and sensory loss and paresthesias affecting digits 4 and 5. However, the ulnar-innervated finger flexors are spared in this syndrome, and in some individuals the hypothenar muscles are less affected than some of the other hand muscles, such as the first dorsal interosseous. (See "Ulnar neuropathy at the elbow and wrist", section on 'Ulnar neuropathy at the wrist'.)
In most cases, the diagnosis of ulnar neuropathy can be confirmed by electrodiagnostic testing or imaging when suspected on the basis of clinical symptoms or signs. There are a number of provocative maneuvers for ulnar neuropathy, but the sensitivity and specificity of these maneuvers appears to be suboptimal. (See "Ulnar neuropathy at the elbow and wrist", section on 'Diagnosis'.)
Patients with mild ulnar neuropathy who typically present with intermittent sensory symptoms and electrodiagnostic features of conduction slowing across the elbow often improve with conservative measures or remain stable over years. Those with persistent sensory loss and weakness without wasting often present acutely (sometimes with a milder preexisting history of intermittent symptoms) and commonly have features of both conduction block and slowing on electrodiagnostic testing. This group often improves over the course of three to six months, based upon clinical and electrodiagnostic measures. Those with persistent symptoms of weakness and numbness beyond six months should be referred for consideration of surgical intervention. (See "Ulnar neuropathy at the elbow and wrist", section on 'Management' and "Ulnar neuropathy at the elbow and wrist", section on 'Initial conservative treatment'.)
The management of ulnar neuropathy at the wrist is directed by the results of the clinical scenario and imaging. Patients with traumatic causes or with evidence of extrinsic or intrinsic neural compression should be referred for consideration of surgical treatment.
Patients with severe weakness, wasting, and persistent sensory loss due to ulnar neuropathy at the elbow or wrist will show evidence of axonal injury on electrodiagnostic testing. In younger patients, or when the presentation is acute (less than six months), consideration should be given to surgical referral. However, for older adult or medically unwell patients, and for patients with chronic (two years or longer) severe involvement, the benefit of surgical intervention is doubtful. (See "Ulnar neuropathy at the elbow and wrist", section on 'Surgery for refractory or severe symptoms'.)
Miscellaneous syndromes — Ulnar neuropathy rarely may occur as the nerve exits the cubital tunnel. In diabetic patients, ulnar neuropathy can occur in the forearm. In vasculitic processes, infarction of the nerve generally occurs just proximal to the elbow.
RADIAL NERVE SYNDROMES
Radial neuropathy at the spiral groove — The radial nerve descends down the medial upper arm before wrapping around the mid-humerus and taking a more posterior course. The nerve is particularly predisposed to compression in the region where it runs adjacent to the humerus, known as the spiral groove. Compression of the nerve in this area often occurs after prolonged pressure on the nerve. The term "Saturday night palsy" has been applied to this disorder since inebriated individuals frequently develop the problem.
On examination, 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. The best way to determine subtle brachioradialis weakness is to have the patient keep the forearm midway between pronation and supination (in a "banging the table" position), asking the patient to flex the forearm against resistance and then assessing the bulk of the muscle by palpation, comparing it with the unaffected side.
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.
Acute radial neuropathies at the spiral groove are sometimes difficult to distinguish from a central nervous system lesion producing arm weakness. Most central disorders that cause arm weakness tend to affect the extensors greater than the flexors. Thus, weakness in extension of the wrist (ie, wrist drop) and fingers may be an ambiguous finding. 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. Most importantly, the brachioradialis should also be weak in a radial nerve lesion, but is typically less affected in a central disorder.
Posterior interosseous neuropathy — The posterior interosseous nerve branches off from the radial nerve just proximal to the elbow and innervates the extensor muscles of the forearm. The radial nerve descends down the forearm as the superficial radial nerve with no motor component, providing cutaneous sensation to the dorsum of the hand.
In most cases, pain is the only significant problem associated with a posterior interosseous neuropathy. Provocative pain with extension of the middle finger and relief of pain with nerve block may help identify mild problems . Persistent pain in cases of severe lateral epicondylitis (tennis elbow) has been attributed to compression of the nerve in this region. (See "Elbow tendinopathy (tennis and golf elbow)".)
Like anterior interosseous neuropathy, posterior interosseous neuropathy can also occur as part of brachial neuritis. (See 'Brachial plexopathy' below.)
A posterior interosseous neuropathy also 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.
Treatment — Conservative treatment is generally the rule for patients with a one-time compression injury to the radial nerve (such as a radial Saturday night palsy). Physical therapy, wrist splinting (to maintain function), and pain management are most important. Prognosis for full recovery is generally good. In a retrospective study of 51 patients with compressive radial neuropathy, follow-up was available for 23, and all experienced complete clinical recovery over a mean of 3.4 months (range 0.5 to 6 months) .
In patients with severe injury secondary to trauma, follow-up examinations and electromyography (EMG) may be warranted. Severe ongoing nerve compression or transection may be difficult to distinguish from a single episode of injury that occurred at the time of trauma. Lack of any improvement, either clinically or electrophysiologically, warrants further imaging or surgical exploration.
In patients with posterior interosseous neuropathy in the forearm, surgical intervention aimed at decompressing the nerve can be helpful if the diagnosis is reasonably secure . However, the possibility that it is a manifestation of neuralgic amyotrophy should be considered. (See "Brachial plexus syndromes", section on 'Neuralgic amyotrophy'.)
PROXIMAL NEUROPATHIES — A number of other isolated focal neuropathies may affect the upper extremity, including suprascapular neuropathy, long thoracic neuropathy, and axillary neuropathy. These disorders are uncommon. Suprascapular neuropathy and axillary neuropathies may present with weakness in arm abduction and external rotation; long thoracic neuropathy usually produces winging of the scapula (picture 1). Sensory loss and paresthesias occur only with axillary neuropathies. Pain is usually present in all of these disorders. Electromyography (EMG) and nerve conduction studies (NCS) identify abnormalities confined to muscles of the affected nerve.
Suprascapular neuropathy — The suprascapular nerve originates from the upper trunk of the brachial plexus (figure 1). It carries sensory fibers from the glenohumeral and acromioclavicular joints, and provides motor supply to the supraspinatus and infraspinatus muscles. Injury most often occurs due to entrapment at the suprascapular notch and less often at the spinoglenoid notch (figure 8) . Shoulder pain is prominent in most patients with impingement at the suprascapular notch, along with weakness of the supraspinatus (shoulder abduction) and infraspinatus (external shoulder rotation) muscles. Atrophy may be evident as well. By contrast, suprascapular nerve injury at the level of the spinoglenoid notch results in painless weakness of external shoulder rotation and atrophy of the infraspinatus.
Direct trauma is a common cause of suprascapular neuropathy, such as can occur from a football tackle, a fall, a motor vehicle accident, or a rotator cuff tear [9,10]. The nerve can also be injured by activities involving stretch, traction, or repetitive movement, as has been reported in weight lifters, volleyball players, baseball players, and gymnasts [11-13]. A concurrent axillary neuropathy may be present, particularly with traumatic etiologies . Rarely, the suprascapular nerve is injured by compression from masses such as a ganglion cyst or tumor. In one study of 27 patients with entrapment of the suprascapular nerve who had perineural masses identified by magnetic resonance imaging (MRI), 21 were ganglion cysts and 5 were malignant tumors .
The diagnosis of suprascapular nerve entrapment may be suspected on the basis of clinical findings including pain, muscle weakness and atrophy, and limited scapulothoracic movement. More severe limitation of shoulder range of motion is seen with concurrent axillary involvement . While electrodiagnostic testing and imaging studies may help confirm a clinical disorder, many cases of suspected suprascapular nerve entrapment have negative studies. In a series of 87 cases of suprascapular neuropathy, approximately 50 percent of patients had no relevant abnormality on shoulder MRI or ultrasound . Thus, continued clinical observation is needed.
Treatment and prognosis vary according to the type of nerve injury . For patients with repetitive trauma, avoidance of the precipitating movement is often sufficient to allow recovery, combined with physical therapy and exercise for preserving range of motion and strengthening the shoulder and rotator cuff muscles. Surgical release of the transverse scapular ligament and arthroscopic suprascapular nerve decompression are options for patients who do not improve with conservative management [16-18]. Surgical excision is indicated for those with a cyst or tumor.
Long thoracic neuropathy — The long thoracic nerve is a pure motor nerve that arises from the fifth, sixth, and seventh cervical nerve roots (figure 1). Dysfunction of the long thoracic nerve leads to paralysis of the serratus anterior muscle, which results in winging of the scapula. To demonstrate winging, the patient presses the outstretched arms against a wall; the involved scapula projects from the thorax as viewed from behind (picture 1). Importantly, winging of the scapula is not specific for a long thoracic neuropathy, as it can also be seen in spinal accessory neuropathies (with trapezius weakness), dorsal scapular neuropathies (causing rhomboid weakness), cervical radiculopathy, and primary muscle diseases.
The main causes of injury to the long thoracic nerve are the following [9,19]:
●Trauma or compression
●Stretch or traction from repetitive activities
In its classic form, neuralgic amyotrophy is characterized by the onset of severe pain followed by patchy weakness in the distribution of a trunk or cord of the brachial plexus or in the distribution of multiple nerves, usually accompanied by winging of the scapula. In some cases of neuralgic amyotrophy, the long thoracic nerve is involved in isolation. (See "Brachial plexus syndromes", section on 'Neuralgic amyotrophy'.)
Trauma to the long thoracic nerve can occur from a direct blow to the shoulder or lateral chest wall (eg, playing football), from invasive procedures (eg, first rib resection, mastectomy with axillary node dissection, scalenectomies, chest tube insertion, infraclavicular plexus anesthesia, and cardiothoracic surgery) [9,20,21]. Some cases that present postoperatively are likely caused by neurovascular compression or traction from upper arm positioning during anesthesia. Nerve compression is the presumed mechanism of injury associated with carrying heavy objects such as backpacks across the shoulder. Stretch or traction to the nerve may occur from repetitive motion related to sports or manual labor, particularly when the arm is in an overhead, outstretched position, and rarely from chiropractic manipulation .
Management and prognosis vary according to the mechanism of nerve injury . Recovery from neuralgic amyotrophy occurs slowly over one to three years (see "Brachial plexus syndromes", section on 'Neuralgic amyotrophy'). Most cases of long thoracic nerve injury caused by carrying or by repetitive activity are incomplete and resolve spontaneously within 6 to 24 months. The patient should avoid the precipitating movement and avoid carrying heavy objects across the shoulder . Physical therapy and exercise are important to maintain range of motion and strengthen trapezius and rhomboid muscles. Long thoracic nerve injury due to trauma is generally severe and recovery is often limited or does not occur.
For those who do not experience functional recovery, surgical procedures may be an option [9,23,24]. These include various combinations of muscle transfers and fascial grafts (eg, transfer of the sternal head of the pectoralis major muscle). There are also a few case reports of successful treatment with nerve transfer using the thoracodorsal nerve or medial pectoral nerve [25,26]. However, functional limitation due to isolated serratus anterior weakness most often is relatively mild and does not require surgical intervention.
Axillary neuropathy — The axillary nerve is derived from the posterior cord of the brachial plexus (figure 1). It carries cutaneous sensory fibers to an oval-shaped area over the lateral shoulder and innervates the deltoid (shoulder abduction) and teres minor (shoulder external rotation) muscles. The most common cause of axillary neuropathy is trauma, usually with shoulder dislocation or humeral fracture . Axillary neuropathy can also occur following general anesthesia or sleep in a prone position with the arms raised above the head. In addition, entrapment occurs rarely in the quadrilateral space, which is formed by the teres minor muscle superiorly, the humerus laterally, the long head of the triceps medially, and the teres major muscle inferiorly [27,28]. The axillary nerve may also be involved as part of the neuralgic amyotrophy syndrome, though seldom in isolation.
The clinical features of axillary neuropathy include a sharply defined region of sensory loss over the lateral shoulder . Weakness is variable and seldom severe, since other muscles assist with shoulder abduction and external rotation.
Conservative management includes physical therapy and exercise to preserve range of motion. Recovery is usually underway by three to four months for patients with incomplete nerve injury. Surgical intervention, including nerve grafting, is an option for patients with severe lesions and those who do not improve in the first few months with conservative measures [29,30], and for those with recurrent shoulder dislocation.
Spinal accessory neuropathy — The spinal accessory nerve is a cranial nerve that is derived from the upper cervical nerve roots and innervates the sternocleidomastoid and trapezius muscles, the latter of which primarily functions as a shoulder stabilizer.
The most common causes of isolated spinal accessory neuropathy include biopsy of the cervical lymph nodes in the posterior triangle and local surgery, such as radical neck dissection . Blunt injuries to the nerve are also common (eg, due to sports or combat). In one report, a spinal accessory neuropathy was attributed to a vigorous massage .
Clinical features of an accessory neuropathy include drooping or depression of the affected shoulder and weakness in abduction [31,33]. Atrophy and weakness of sternocleidomastoid are present in more proximal spinal accessory nerve lesions, while more distal lesions lead to atrophy and weakness of the trapezius muscle. Sensory loss is not a feature since the spinal accessory nerve is a pure motor nerve. However, pain is commonly present, perhaps caused by traction on the brachial plexus . Prominent winging of scapula is usually observed .
Weakness of the shoulder is most easily demonstrated by having the patient abduct the arm through 180 degrees; in a patient with accessory neuropathy, the last 90 degrees of this maneuver cannot be accomplished. Importantly, the strength of other shoulder muscles such as the deltoid, rhomboids, and serratus anterior cannot be assessed accurately due to the loss of shoulder stabilization.
The prognosis will vary by cause. In more severe lesions, muscle transfers can help stabilize the scapula and improve function.
Musculocutaneous neuropathy — The musculocutaneous nerve arises from the lateral cord of the brachial plexus and contains fibers from the C5, C6, and C7 nerve roots. After piercing the coracobrachialis muscle, it courses down the front of the arm between the biceps and brachialis and continues into the forearm as the lateral antebrachial cutaneous nerve. It innervates the coracobrachialis, biceps, and brachialis muscles and supplies cutaneous sensation to the lateral forearm. Clinical features thus include weakness of elbow flexion with associated sensory loss over the lateral forearm.
Isolated lesions of the musculocutaneous nerve are rare, but the nerve can be injured with direct trauma, shoulder dislocation, strenuous exercise, or malpositioning of the arm during anesthesia [34-37].
BRACHIAL PLEXOPATHY — The brachial plexus (figure 1) is the most complex structure of the peripheral nervous system . It is vulnerable to trauma and may be affected secondarily by disorders involving adjacent structures. Most brachial plexus disorders show a regional involvement rather than involvement of the entire brachial plexus. (See "Brachial plexus syndromes".)
Localizing a problem to a specific region of the brachial plexus is usually the most important first step in patients with brachial plexopathy. Once that is achieved, it is typically relatively straightforward to identify a specific etiology.
A few simple rules can lead to accurate localization of problems to the brachial plexus:
●Weakness generally should have a "myotomal" pattern: weakness in C8 to T1 muscles suggests the possibility of a lower trunk/medial cord problem; weakness in C5 and C6 muscles raises the possibility of an upper trunk/lateral cord problem; weakness isolated to a single nerve is unlikely to be of plexus origin, except in cases of brachial neuritis.
●Involvement of muscles innervated by the radial or axillary nerves (eg, deltoid, triceps, brachioradialis, wrist extensors, wrist flexors) is consistent with involvement of the posterior cord.
●Isolated middle trunk plexopathies are almost nonexistent; usually some involvement of the lower or upper trunk is also present. A C7 radiculopathy is far more likely.
●Fixed sensory loss extending into the medial forearm is consistent with a lower trunk/medial cord plexopathy; sensory loss extending into the lateral forearm is consistent with an upper trunk/lateral cord plexopathy. The skin in these regions is innervated by nerves that branch off directly from the plexus.
●Weakness of serratus anterior (causing winging of the scapula), the infra- and supraspinatus (causing weakness of arm external rotation and initial abduction), or the rhomboids (retraction and elevation of scapula) makes a radiculopathy or component of radiculopathy more likely since all of these muscles are innervated by nerves that branch off at the very proximal plexus or from the spinal nerves themselves. Brachial neuritis is an important exception to this rule since the serratus anterior is often involved.
Specific disorders of the brachial plexus are reviewed in detail separately. (See "Brachial plexus syndromes".)
CERVICAL RADICULOPATHY — A radiculopathy is a pathologic process affecting the nerve root. Cervical radiculopathy is a common cause of both acute and chronic neck pain. This condition is reviewed briefly here, and discussed in greater detail elsewhere. (See "Clinical features and diagnosis of cervical radiculopathy".)
Most radiculopathies arise from nerve root compression. The two predominant mechanisms of compressive cervical radiculopathy are cervical spondylosis and disc herniation. Lower cervical roots, particularly C7, are more frequently affected by compression than higher cervical roots.
Some causes of noncompressive radiculopathy include infection (especially herpes zoster and Lyme disease), nerve root infarction, infiltration by tumor, infiltration by granulomatous tissue, root avulsion, and demyelination.
Pain in the neck, shoulder, or arm occurs in nearly all patients with cervical radiculopathy, but it is usually not helpful for localizing the precise level of the affected root. The pain may be atypical and present as chest pain (pseudo-angina), breast pain, or pain in the face. Head-turning, coughing, or sneezing may exacerbate symptoms.
In patients with suspected cervical radiculopathy, a major goal of the neurologic evaluation is to look for weakness and sensory disturbance in myotomal and dermatomal patterns. Typical clinical findings of solitary root lesions are summarized in the table (table 1).
Neuroimaging and electrodiagnostic testing is indicated when localizing signs and symptoms suggest a nerve root injury or when there are persistent symptoms that do not resolve with conservative therapy.
The management of patients with cervical radiculopathy is discussed separately. (See "Treatment and prognosis of cervical radiculopathy".)
Focal amyotrophy — Focal or monomelic amyotrophy (including one form known as Hirayama disease) is an unusual disorder, characterized by pure motor weakness of one extremity (or both in some cases of Hirayama disease), which represents a restricted form of motor neuron disease. (See "Diagnosis of amyotrophic lateral sclerosis and other forms of motor neuron disease", section on 'Monomelic amyotrophy'.)
Mononeuropathy multiplex — Ischemic lesions affecting multiple nerves may produce a confusing clinical picture. However, in most patients, more widespread nerve involvement (including in the legs) is present.
Treatment of the underlying disease remains the rule for management of mononeuropathy multiplex. Recovery can be remarkably good in patients with forms responsive to immunosuppression despite initial severe nerve damage. Patients with varied causes of vasculitis (including Churg-Strauss disease, rheumatoid arthritis, granulomatosis with polyangiitis, among others), may have significant improvement in neurologic disability in response to immunosuppression. Mononeuropathy multiplex due to vasculitis, either systemic or localized to the nerves only, is discussed in more detail separately. (See "Clinical manifestations and diagnosis of vasculitic neuropathies".)
Multifocal motor neuropathy — Multifocal motor neuropathy (MMN), also known as multifocal motor neuropathy with conduction block, is a rare immune-mediated demyelinating neuropathy characterized by progressive asymmetric weakness and atrophy without sensory abnormalities, a presentation similar to that of motor neuron disease. (See "Multifocal motor neuropathy".)
The most common clinical presentation of MMN is one of subacute onset with asymmetric weakness and lower motor neuron signs producing arm and hand weakness without associated sensory loss. The neuronal involvement in MMN is typically patchy, with some nerves unaffected and others severely involved. Motor nerve conduction studies (NCS) usually show evidence of conduction block. Sensory conduction through the same segment of nerve is normal. Elevated titers of anti-GM1 antibodies are present in 30 to 80 percent of patients. (See "Multifocal motor neuropathy", section on 'Clinical features'.)
MMN is treatable with intravenous immune globulin and other forms of immunosuppression. (See "Multifocal motor neuropathy", section on 'Treatment'.)
Zoster radiculoganglionitis — Patients with herpes zoster may develop, in addition to a painful rash, weakness and sensory loss in a nerve distribution close to that of the rash. Inflammation involves the nerve roots and dorsal root ganglion, potentially producing prominent neurogenic injury. Occasionally an associated myelopathy is also present.
●Mechanisms of nerve injury – The major mechanisms of upper extremity peripheral nerve injury are compression, transection, ischemia, inflammation, neuronal degeneration, and radiation exposure. (See 'Etiologies' above.)
•Electromyography and nerve conduction studies are useful for identifying and classifying peripheral nerve disorders affecting the upper extremity. (See 'Overview of diagnostic testing' above.)
•Magnetic resonance imaging of the cervical spine is useful to identify disc herniation or degeneration and the degree of nerve root compression as well as to exclude the possibility of a mass lesion. (See 'Imaging' above.)
•Neuromuscular ultrasound can be helpful in assessing individual peripheral nerves in patients who present with an unusual upper extremity mononeuropathy.
•Laboratory testing and cerebrospinal fluid analysis are generally reserved for patients with conditions associated with an inflammatory, infectious, or endocrine source. (See 'Laboratory testing' above and 'Lumbar puncture' above.)
•Carpal tunnel syndrome is the most common upper extremity mononeuropathy. Typical symptoms include pain or paresthesia in a distribution that includes the median nerve territory, with involvement of the lateral portion of the hand (figure 4). The symptoms are typically worse at night and characteristically awaken affected individuals from sleep. (See 'Carpal tunnel syndrome' above.)
•Less common median nerve syndromes include entrapment where the median nerve passes through the pronator teres muscle and injury to the anterior interosseous nerve that branches at the elbow. (See 'Pronator teres syndrome' above and 'Anterior interosseous neuropathy' above.)
●Ulnar neuropathy – Ulnar neuropathy at the elbow (figure 5) is the second most common compression neuropathy affecting the upper extremities. Symptoms include sensory loss and paresthesias over digits 4 and 5 (figure 6) and weakness of the interosseous muscles of the hand in severe cases. (See 'Ulnar nerve syndromes' above.)
●Radial nerve syndromes – With compression of the radial nerve at the spiral groove, the triceps retains full strength, but there is weakness of the wrist extensors (ie, wrist drop), finger extensors, and brachioradialis. Sensory loss is present over the dorsum of the hand and may extend up the posterior forearm. With posterior interosseous neuropathy, forearm pain and weakness of finger dorsiflexion is typical. (See 'Radial nerve syndromes' above.)
●Proximal neuropathies – Several uncommon proximal focal neuropathies of the upper extremity typically present with pain and sensorimotor impairment. These include suprascapular neuropathy, long thoracic neuropathy, axillary neuropathy, spinal accessory neuropathy, and musculocutaneous neuropathy. (See 'Proximal neuropathies' above.)
●Brachial plexopathy – The brachial plexus (figure 1) is vulnerable to trauma and may be affected secondarily by disorders involving adjacent structures. Most brachial plexus disorders show a regional involvement rather than involvement of the entire brachial plexus. (See 'Brachial plexopathy' above.)
●Cervical radiculopathy – Cervical radiculopathy is a common cause of both acute and chronic neck pain. Most radiculopathies arise from nerve root compression due to cervical spondylosis and/or disc herniation. Lower cervical roots, particularly C7, are more frequently affected by compression. Typical clinical findings of solitary root lesions are summarized in the table (table 1). (See 'Cervical radiculopathy' above.)
●Other syndromes – Additional uncommon peripheral nerve syndromes affecting the upper extremities include focal amyotrophy, mononeuropathy multiplex, multifocal motor neuropathy (MMN), and zoster radiculoganglionitis. (See 'Miscellaneous' above.)
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