RENEW OR SUBSCRIBE TO PPM
Subscription is FREE for qualified healthcare professionals in the US.
9 Articles in Volume 14, Issue #8
New Perspectives on Neurogenic Thoracic Outlet Syndrome
Dialysis, Opioids, and Pain Management: Where’s the Evidence?
Difficult to Treat Chronic Migraine: Outpatient Medication Approaches
Difficult to Treat Chronic Migraine: The Bipolar Spectrum and Personality Disorders
Arachnoiditis Part 2—Case Reports
Editor's Memo: The Conundrum of Epidural Corticosteroid Injections
Ask the Expert: Central Sensitization
Ask the Expert: NSAIDs After Bariatric Surgery
Letters To the Editor: September 2014

New Perspectives on Neurogenic Thoracic Outlet Syndrome

The quality of life for patients with neurogenic thoracic outlet syndrome is profoundly diminished. Emerging evidence supports minimally invasive chemodenervation of the cervicothoracic musculature with onobotulinum toxin as a treatment option.

The definition, incidence, diagnosis, and treatment of thoracic outlet syndrome (TOS) are somewhat controversial. Originally coined in 1956, the term TOS indicated a “compression of the neurovascular structures in the interscalene triangle corresponding to the possible etiology of the symptoms.”1 The controversy is centered on the fact that TOS refers to the anatomy or location of the problem without identifying the cause—either vascular or neurogenic.

Therefore, TOS generally is defined as a group of disorders caused by compression of the brachial plexus, subclavian artery, or subclavian vein in the thoracic outlet, the area between the clavicle (collarbone) at the base of the neck and the first rib, including the front of the shoulders and chest. TOS is a progressive condition marked by the impingement of the nerves and blood vessels that feed the thoracic outlet. Compression of the subclavian muscle, which is known to compress the subclavian artery, reduces bloodflow to the carotid arteries and the vertebral arteries. This may lead to intractable migraine, one of the first symptoms of TOS.

Neurogenic TOS (NTOS), the most common form of TOC, can result from inadequate space caused by scalene hypertrophy, fibrosis, or congenital abnormalities, such as the occurrence of a cervical rib. Other causes include repetitive motions that can enlarge or change the tissue in or near the thoracic outlet (similar to carpel tunnel syndrome). These repetitive activities include assembly line work, typing, and other movements; hyperextension-flexion injuries; neck injuries from motor vehicle accidents (whiplash); and sports-related injuries, particularly from swimming, baseball (pitching), weightlifting, and volleyball.

Frequent symptoms of NTOS include numbness; tingling in the fingers; pain in the neck, shoulder or arm; muscle spasms around the scapula; headaches; and weakness in the upper extremities (Table 1).2

Pathophysiology

In many patients, the etiology of NTOS involves a combination of a “double hit” of a congenital predisposition and an injury to the area that compromises the outlet. The narrowed space affects the scalene muscles, the brachial plexus, the long thoracic and suprascapular nerves, and the stellate ganglion (Figure 1).

Although the notion of NTOS as a complex spectrum disorder provokes some controversy in the field, its impact on patients is beyond dispute. Data indicate that the quality of life for a patient with untreated TOS is as impaired as that of someone with chronic heart failure.3

TOS has been divided into 3 forms:

  • Neurogenic TOS (brachial plexus compression)
  1. True neurogenic TOS
  2. Common neurogenic TOS
  • Arterial (subclavian artery compression)
  • Venous (subclavian vein compression)

As noted, nearly all cases of TOS (95%) are neurogenic in origin. NTOS is an underappreciated and often overlooked cause of shoulder and neck pain and numbness. Like patients with other chronic pain conditions, patients with untreated neurogenic TOS experience a diminished quality of life, reduced financial well-being, functional limitations, and an increased risk for depression and anxiety.4-6

True NTOS, which is confirmed with objective findings, accounts for only 1% of cases, whereas common NTOS, which has symptoms suggestive of brachial plexus compromise but no objective findings, makes up 99% of neurogenic cases of TOS.7,8 The remaining cases of TOS are arterial (1%) and venous (3%-5%).1

Neurogenic TOS occurs in an estimated 3 to 80 per 1,000 individuals, the wide range reflecting the lack of confirmation in many patients with signs and symptoms indicative of the condition. Women with NTOS outnumber men by 3 to 4:1. The syndrome is particularly common in people who perform repetitive tasks with their upper extremities, such as violinists, data entry personnel, and workers on assembly lines. Athletes with repetitive overhead arm motion, including volleyball players, swimmers, baseball pitchers, and weightlifters, also are at increased risk, as are people who have experienced neck trauma.9

Histologic studies suggest that injury to either the anterior scalene muscle (ASM) or the middle scalene muscle are the main causative factors of NTOS. Muscle fibrosis is a prime finding on examination of excised scalene muscles, with NTOS patients having 3 times as much scar tissue as unaffected subjects.8-10

The ASM derives from the transverse processes of the C3-C6 vertebrae. The muscle, which attaches to the first rib, serves as an accessory muscle of respiration, and also rotates the neck slightly. Spasm of the ASM puts traction on the brachial plexus and causes edema of the muscle and nerves, which, in turn, limits the space of the outlet. Development of scar tissue and fibrosis of the ASM further worsen neural compromise and perpetuate pain.8,11

Targeting treatment to relieve tension and spasm of the ASM can interrupt the chain of events that leads to NTOS.

Diagnosis

There is no one standard for the diagnosis of TOS. The diagnosis of NTOS can be difficult because it often has a nonspecific clinical presentation. In a classic case, the patient will complain of pain originating in the area of the shoulder and radiating along the inner aspect of the arm. Other common symptoms involve pain in the neck; the trapezius, mastoid, and anterior chest wall muscles—all from upper plexus compression (C5-C7). Physical examination will reveal tenderness in the scalene muscles, trapezius, and chest wall. Patients may have a positive Tinel sign over the brachial plexus in the neck, reduced sensation in the fingers to light touch, and positive provocative maneuvers.9

Complicating the differential diagnosis, however, is that the entire arm often is involved without dermatomal preference. The clinician must distinguish cervical radiculopathy from disk herniation or stenosis and rule out carpal tunnel syndrome.

A thorough history and physical examination are key to accurate diagnosis of NTOS. Testing for NTOS is unreliable. Ancillary testing lacks sensitivity and specificity. Similarly, provocative testing, including the Adson maneuver,12 has unknown reliability and specificity. The Adson maneuver, in particular, produces many false positive results and no longer is considered useful for identifying patients with NTOS.13

Provocative maneuvers, nerve tension tests, and thumb pressure over the brachial plexus can assist in the determination of NTOS, but the elevated arm stress test, or Roos stress test, is perhaps the most reliable indicator.13 Another potentially useful diagnostic test includes the Spurling test to identify cervical disk disease.8,14,15

Imaging Studies

Patients with NTOS often have normal results on electromyelography (EMG) and nerve conduction tests. However, these studies can be used to exclude other causes of neuropathic symptoms, such as radiculopathy, carpal tunnel syndrome, cubital tunnel syndrome, and polyneuropathy.

A chest x-ray may be warranted to identify cases of cervical rib. Magnetic resonance imaging and computed tomography (CT) also can help to rule out conditions that mimic NTOS.

Some evidence suggests that a medial antebrachial cutaneous nerve conduction study can detect milder cases of NTOS. This test measures sensory function of the lower trunk of the brachial plexus and often yields positive results in patients with negative findings on an EMG or nerve conduction tests. However, additional studies are required to validate the utility of the test.9,16

Anterior Scalene Block

First described in 1939, the anterior scalene block (ASB) is an intramuscular confirmatory test for NTOS. The block paralyzes the muscle in spasm, allowing the first rib to descend and decompresses the thoracic outlet.17 A positive response to an ASB test correlates well with good surgical outcomes, whereas temporary muscle relaxation helps predict benefit from decompression. In one study, EMG-guided block provided relief in 94% of patients who underwent surgery.18

A variety of imaging techniques can improve the success of ASB. CT guidance for scalene injections, in particular, has been shown to minimize Horner’s sign, dysphonia, brachial plexus block, and dysphagia.17

Treatment

Conservative

Conservative treatment for NTOS involves steps to minimize pressure on the brachial plexus, restoring muscle balance in the neck, and improving neural mobility. Correcting ergonomic issues and poor posture can help, as can nerve glides, stretching exercises, and biofeedback. A 14-month course of postural correction and strengthening of the shoulder girdle led to significant reductions in pain and high patient satisfaction in one study.19

Physical Therapy

Some data support the use of heat packs, exercise programs, and cervical traction for the treatment of NTOS.20,21 A course of inpatient rehabilitation, followed by a home exercise program, appears to have a high rate of satisfaction among patients who have undergone this regimen. However, data suggest that, in general, no single approach to physical therapy is sufficient on its own. Indeed, without other interventions, physical therapy may lead to worse outcomes for some patients. In one study, 42 patients (37 women, 5 men) diagnosed with NTOS who had participated in physical therapy at least 6 months prior to the study were selected.22 At the end of the follow-up period, 25 patients reported symptomatic improvement, 10 reported that they were the same, and 7 patients had worse symptoms. Poor overall outcome was related to obesity (P<0.04), workers’ compensation claims (P<0.04), and associated carpal or cubital tunnel syndrome (P<0.04). Neck and shoulder symptoms were improved in 38 patients. Improvement in hand and arm pain was significantly better in those without concomitant distal nerve compression (P<0.06).22

Cognitive behavioral therapy is an important adjunct to treatment, helping patients modify their perception of pain, reframe their experience in positive terms, and minimize catastrophizing about their condition.

Pharmacologic Approaches

A variety of pharmacologic agents can provide relief of symptoms, if not improvement in the physiologic underpinnings of NTOS. These include non-steroidal anti-inflammatory drugs (eg, ibuprofen [Advil, Motrin, others]), muscle relaxants (eg, tizanidine [Zanaflex, others]), tricyclic antidepressants (eg, nortriptyline [Pamelor, others]), serotonin-norepinephrine reuptake inhibitors (eg, duloxetine [Cymbalta, others]), and membrane stablizers (eg, gabapentin [Neurontin, Horizant, others]). If the patient’s quality of life deteriorates during pharmacologic treatment and other therapies fail, sustained-release opioids are an option.9

Chemodenervation

Injection of onobotulinum toxin Type A (Botox) is a relatively new and promising approach to the treatment of NTOS.23 Studies indicate that onobotulinum toxin is safe and effective for an increasing number of neuromuscular ailments. Approved indications for onobotulinum toxin injections include hemifacial spasm, blepharospasm, strabismus, and chronic migraine, among others. Successful off-label use also has been described for lumbosacral myofascial pain, piriformis syndrome, and lateral epicondylitis.

Administration of onobotulinum toxin for NTOS involves a single, low-dose injection (20 units) into the ASM under CT-guidance. In one study, 27 patients with NTOS experienced substantial pain relief for up to 3 months following low-dose injections of onobotulinum toxin under CT guidance.23 The primary outcome was pain and sensation on a visual analog scale (VAS) at 1, 2, and 3 months after therapy. Short Form McGill Pain Questionnaire scores were evaluated before treatment and at 1, 2, and 3 months after therapy. Patients reported substantial relief from treatment at both 1 and 2 months, and statistically and clinically significant relief in both sensory and VAS scores at the 3-month point (29% and 15%, respectively).23

Onobotulinum toxin reduces muscle overactivity in the area of the injection by blocking the release of acetylcholine, weakening the muscle for as long as 3 to 4 months. The toxin also may reduce pain and inflammation in some patients, perhaps by inhibiting the release of neuropeptides—particularly substance P and glutamate—that are implicated in nociceptive transmission and central sensitization.24,25 Some evidence suggests that onobotulinum toxin can improve wound healing and reduce scarring in injured muscles.5,26

Injections of onobotulinum toxin represent a minimally invasive approach for patients hoping to avoid surgery, or a bridge to surgery for those seeking to delay the procedure. Successful injections may obviate the need for surgery—and the potential complications from surgery—and limit the time patients must take off from work, home duties, and other activities of daily living. This benefit can be substantial because the common course for surgical patients involves 8 weeks of physical therapy starting 2 weeks after the procedure, necessitating 2 to 3 months leave from work, as well as no heavy lifting (>10 pounds) for 6 months.5

Although chemodenervation can be performed using multiple imaging modalities, the evidence for CT guidance is strong (Table 2). CT allows clinicians to visualize nearby anatomy (in real-time in the case of CT fluoroscopy), and, unlike ultrasound, it is not vulnerable to obscuring by adiposity or osseous structures. CT imaging is fast, accurate, reliable, and safe, leading to a higher percentage of successful anesthetic blocks compared to other modalities: 82% versus 38% for ultrasound, 18% for EMG + fluoroscopy, and 72% for EMG alone.17,27,28 This advantage is borne out by the high rate of improvement after surgery associated with CT-guided blocks (70%) to confirm true cases of neurogenic TOS.5,23

Keeping exposure time to 60 seconds or less limits the amount of ionizing radiation patients receive.

Surgical Decompression

Multiple approaches to surgical decompression for NTOS are available, although comparative efficacy data for the techniques do not exist. Studies suggest that initial rates of success are high, approaching 90%; however, complications occur in more than 30% of patients and longitudinal data show a 60% recurrence of symptoms within the first year after surgery and 80% within the second year. In addition, 60% of patients report persistent disability within the first year after surgery.29

Conclusion

Neurologic TOS is the most common type of TOS, as well as the most often overlooked and misdiagnosed form of the condition. It causes persistent pain, impaired function, and emotional distress. If untreated, the quality of life for patients with NTOS is profoundly diminished. Emerging evidence supports minimally invasive chemodenervation of the cervicothoracic musculature with onobotulinum toxin. Clinicians and patients should consider this approach before attempting surgical decompression.

Last updated on: July 21, 2015
close X
SHOW MAIN MENU
SHOW SUB MENU