Thoracic outlet syndrome: a review for the primary care provider

Etiology of thoracic outlet syndrome

TOS is a global term utilized to describe a variety of symptoms associated with compression of the neurovascular bundle that traverses the space defined by the cervical column, upper ribs, and clavicle. The compression of these structures can lead to a multitude of clinical symptoms affecting the shoulder girdle, neck, and upper extremity (Figure 2) [4]. Anatomically, compression of the neurovascular bundle traditionally occurs at three specific areas with distinct landmarks:

1. Scalene triangle: compression occurs as the brachial plexus and traverses the space between the middle and anterior scalene muscles and the first rib.

2. Costoclavicular space: compression occurs in the space between the clavicle and the first rib.

3. Pectoralis minor space: the area formed from the pectoralis minor muscle anteriorly and the rib cage posteriorly. This area is not considered to be part of the thoracic outlet proper; however, entrapment of the neurovascular bundle within this space is included in the etiologies of the clinical syndromes associated with TOS and may be as common as entrapment at the scalene triangle [5].

Figure 2:

An illustration of the relevant neurovascular anatomy in the anterior supraclavicular neurosurgical approach to the brachial plexus and subclavian vessels for thoracic outlet syndrome. This file is licensed under the creative commons Attribution-ShareAlike 3.0 Unported license. Source: Nicholas Zaorsky, MD. Zaorsky, M. Thoracic outlet. https://commons.wikimedia.org/wiki/File:Wikipedia_medical_illustration_thoracic_outlet_syndrome_brachial_plexus_anatomy_with_labels.jpg.

Figure 3:

(A) Upper limb tension test (ULTT) position 1. The patient may be seated or standing with arms abducted to 90° and elbows extended. (B) ULTT position 2. While in position 1, the patient is asked to extend their wrists. (C) ULTT position 3. The patient is shown with his head tilted to the right; repeat with head tilted to left to complete exam. (D) Elevated arm stress test (EAST) position 1. The patient may be seated or standing with arms abducted to 90° and elbows flexed. The shoulders should be externally rotated. (E) EAST position 2. Instruct the patient to continuously open and close their fists. (F) Adson’s test. While seated, the patient’s arm is abducted and externally rotated with the elbow extended. The examiner monitors the patient’s radial pulse as the patient is instructed to take a deep breath while rotating and slightly extending the head toward the side being tested.

The common etiologies of TOS have been classified as being either congenital, traumatic, or functionally acquired with the following being the most encountered:

1. Congenital: cervical or first rib.

2. Traumatic: whiplash injuries, motor vehicle accidents.

3. Functional: vigorous, repetitive upper-extremity activity [6].

Clinical presentation

Patients present with a constellation of symptoms that may manifest as pure neurological symptoms or vascular symptoms or a combination of both. Of the three forms of TOS, nTOS has been reported to represent up to 95.0% of cases [7, 8]. As such, early recognition of the signs and symptoms of nTOS is an important step in preventing disease progression and developing a proper treatment plan. Arriving at a diagnosis of nTOS begins with a proper history and physical examination, followed by special tests to confirm the diagnosis. Patients presenting with nTOS often have a history of neck trauma preceding their symptoms, with automobile accidents, postural decompensation, and repetitive work stress being the most common [11, 12].

Biomechanical factors should be taken into consideration and can serve as diagnostic tools, particularly those of the shoulder joint and pelvis. Muscle imbalance, such as hypertrophied pectoralis minor or hypertrophied scalene and sternocleidomastoid muscles, can directly contribute to the entrapment of the brachial plexus, subclavian artery, and vein. Pelvic alignment affects posture, including head, neck, and upper thoracic spine alignment, thus indirectly contributing to the function of the thoracic outlet. For example, an anterior pelvic tilt due to tight hip flexors may cause an increased lordosis of the lumbar spine and a compensatory kyphosis of the thoracic spine. This may contribute to the shoulders being rolled forward with shortening of the pectoralis minor muscles and tightening of the cervical muscles, ultimately entrapping the cervical brachial plexus and vasculature [12, 13]. Evaluating and treating overall posture and addressing muscle imbalances may help minimize entrapment and ease the symptoms of TOS. A trauma history can help focus the examination. For example, in patients who have undergone whiplash injury, abrupt flexion-extension motion may lead to instability of the atlantoaxial joint, causing the surrounding sternocleidomastoid and scalene muscles to shorten to compensate for the instability. Such a muscle imbalance could potentially lead to entrapment of the thoracic outlet structures [12].

Data on the incidence of specific symptoms was variable and often limited by small sample sizes; however, Sanders, Hammond, and Rao [8] reported the following incidence of symptoms with regard to the patients studied (n=50): paresthesias (98.0%), trapezius pain (92.0%), supraclavicular pain (76.0%), chest pain (72.0%), shoulder and arm pain (88.0%), and occipital headaches (76.0%). Balderman et al. [14] reported that the most common symptoms were upper-extremity pain (99.0%), the exacerbation of symptoms by arm elevation (97.0%), localized supraclavicular or subcoracoid tenderness to palpation (96.0%), and upper-extremity and/or hand paresthesias (94.0%) in new patient referrals (n=183, mean age 37.1). In their study, 107 (71.0%) of the patients were women [14].

Although the presenting symptoms associated with nTOS are highly variable and depend on the underlying etiology, the most common principal symptom is pain in the neck, upper back, shoulder, arm, and/or hand [8, 14]. This pain should be nonradicular in nature and be present during activities, as well as at rest [15]. Lastly, the pain should be reproducible by provocative testing, which is discussed below.

The presenting pain pattern can be utilized to further identify nTOS as that occurring due to compression of the upper (C5-C7) or lower (C8-T1) trunks of the brachial plexus. While patients can present with both upper and lower plexus involvement, Atasoy [16] noted that the lower and combined types comprised 85–90% of all TOS cases (n=750) presenting for surgical intervention of the same.

In patients presenting with upper plexus compression, symptoms are often supraclavicular with radiation to the ipsilateral face, head, upper chest, periscapular region, or radial nerve distribution [17]. Additionally, these patients may complain of hemicranial headaches and “stuffy” ears despite a negative otologic examination [18].

Patients with compression of the lower plexus, which is more common, will often present with complaints of pain along the ulnar side of the arm and hand accompanied by symptoms in the anterior shoulder and axilla [17]. Additionally, lower plexus injury may cause pain radiation into the anterior chest that can mimic cardiac angina, occipital headaches, and a sleeve-like numbness that awakens patients during the night [18].

Numbness and/or paresthesia are common findings in patients with nTOS. Sanders et al. [8] found paresthesia to be present in 98.0% of the patients studied (n=50), with 58.0% of those involving all five fingers, 26.0% involving the fourth and fifth fingers, and 14.0% involving the first to third fingers. Patients will often describe this as a feeling of “numbness” or “tingling.”

Although isolated nTOS is not associated with compression of the subclavian artery, patients still may present with Raynaud’s phenomenon, which presents as a coolness of the hand with associated color changes. In contrast to aTOS, in which color changes and other symptoms are caused by arterial ischemia, Raynaud’s in the setting of nTOS is thought to be caused by an overactive sympathetic nervous system response triggered by irritation of sympathetic nerve fibers that run along the nerve roots of C8 and/or T1 and the lower trunk of the brachial plexus [8]. This anatomical relationship provides an opportunity for the use of manipulative treatment modalities that aim to decrease sympathetic tone to the upper limb.

Special tests

Within the physical examination, numerous special tests have been utilized to arrive at a diagnosis of nTOS. Of these, the most commonly utilized are the elevated arm stress test (EAST), upper limb tension test (ULTT), and Adson’s test [19]. It is important to note that although a single positive provocative test is not enough to diagnose nTOS, a negative ULTT provides strong evidence against the diagnosis of brachial plexus compression [20]. Supporting this are the results from Sanders et al. (n=50) [8], showing that of those patients with positive physical findings consistent with nTOS, 98.0% had a positive ULTT. Recommendations set forth by the Journal of Vascular Surgery in 2016, which set to standardize the diagnosis of nTOS, state that arriving at a diagnosis of nTOS is best achieved through the use of ULTT and EAST tests [9]. Although the Adson’s test when utilized alone has been shown to have a low specificity, Gillard et al. [21] showed a rise of the diagnostic specificity to 82.0% (n=48) when utilized in combination with the EAST test. A positive EAST test and Adson’s test may indicate vascular compression within the scalene triangle but should be interpreted with caution. Each of these tests are described in more detail in Table 2.

Osteopathic structural exam

An osteopathic structural evaluation can reveal direct and indirect myofascial contributors to the TOS symptoms. A common component of postural decompensation that contributes to TOS begins with shoulder protraction in the anterior/inferior direction, which shortens the sternocleidomastoid and the scalene and pectoral muscles, and elevates the upper ribs, narrowing the costoclavicular space [22]. Cervical spine somatic dysfunctions can create facilitation of the nerve roots and affect the tone of the cervicobrachial musculature [23]. Kyphoscoliosis will increase the lordosis of the cervical spine and compress the thoracic outlet space. Thoracic vertebral somatic dysfunctions can create facilitation of the sympathetic innervation of the upper extremities, leading to increased muscular tone and vasoconstriction. Extension somatic dysfunctions of the upper thoracic spine are often associated with TOS symptoms of upper-extremity numbness. Sacral base dysfunction can cause compensatory lumbar scoliosis, which can increase the thoracic kyphosis. Like most structural diagnoses, thoracic outlet symptom etiology is often multifactorial [23]. Tissue texture changes and restrictions in the cervical spine from C2-C7, thoracic T1, rib 1, thoracic inlet, clavicle, and scalene muscle should be evaluated based on patient presentation.

Diagnostic testing for clinically suspected TOS

The diagnosis of TOS begins with a thorough history and physical exam. Imaging and electromyographic (EMG) studies are helpful to confirm the diagnosis, delineate between neurogenic and vascular TOS (arterial and venous), identify the site of compression, and rule out bony anatomical anomalies [6].

Radiographic studies

Initially, plain radiographs of the chest and cervical region may be performed to rule out anatomical abnormalities and structural variants such as cervical ribs, malunion of clavicular fractures, elongated transverse processes, or tumors within the thoracic cavity [15, 19, 24].

Further investigation requires the use of ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI). Per the 2015 American College of Radiology Appropriateness Criteria for imaging in the diagnosis of TOS, ultrasound is a cost-effective tool and visualization of the vessels is a strength, but the sonographic diagnosis of compressive effects upon the brachial plexus is challenging and may miss regional pathology, such as a Pancoast tumor or cervical spondylopathy [25]. Noncontrast MRI can be sufficient to diagnose nTOS, whereas magnetic resonance (MR) or CT angiography are the best modalities to confirm venous or arterial TOS [25].

To diagnose a vascular form of TOS with magnetic resonance angiography (MRA), there must be evidence of endothelial damage such as thrombi in the subclavian or axillary vein, fixed stenosis at a site of compression, or engorged collateral veins for vTOS. For aTOS, there is usually an aneurysm in the subclavian artery, fixed stenosis at the compression site, thrombi, signs of emboli in the corresponding extremity, or larger than normal collateral arteries. A major indicator of both vTOS and aTOS is vessel narrowing with abduction of the affected arm [26].

It is important to note that images should be taken in both the neutral position (supine with arms to the side) and in a hyperabducted position (arms above head and externally rotated) for the diagnosis of TOS. Narrowing of the subclavian vein diameter by 50% and subclavian artery by 30% during abduction is diagnostic of vTOS and aTOS, respectively [27].

nTOS is mostly a clinical diagnosis, although edema and the loss of fat surrounding the brachial plexus with arm abduction is usually evident on MRI [26].

Electrodiagnostic studies

Patients presenting with TOS can present with upper and lower trunk or mixed findings, and the importance of a complete clinical history and physical examination cannot be overstated. Once anatomical variants, structural abnormalities, and direct compression of the brachial plexus have been ruled out as the source of symptoms, EMG can be useful in differentiating the source of upper and lower trunk symptoms and confirming the diagnosis.

Electrodiagnostic data obtained in patients with surgically verified nTOS noted evidence of axonal loss and diminished nerve conduction amplitude in the distribution of the medial antebrachial cutaneous (MABC) nerve, which relies almost solely on fibers from T1. Abnormalities were also seen in nerve conduction of the median motor nerve, particularly the motor innervation to the thenar muscles, which rely mostly on T1 fibers and less on those from C8 [28].

Given these findings, electrodiagnostic testing appears useful in confirming the clinical findings consistent with lower trunk involvement. A comprehensive electrodiagnostic examination of the involved limb with contralateral comparison studies is imperative to diagnose this disorder accurately [28]. For example, in a patient presenting with numbness and paresthesia over the ulnar portion of the forearm, the expectation would be to find a diminished amplitude in MABC nerve conduction and abnormalities in the median motor distribution. Similarly, abnormalities in the median motor nerve supply are often seen on nerve conduction studies in patients with thenar atrophy because the thenar muscles rely primarily on T1 fibers [29].

Treatment options for TOS

Treatment for TOS may begin with conservative measures; however, arterial and venous forms often require more aggressive treatments, because they often present with signs of venous obstruction and/or limb ischemia [30]. The authors would like to point out that due to the relative rarity of TOS, reported data regarding conservative treatment options for TOS, specifically nTOS, is based primarily on retrospective clinical observations and case reports. No randomized controlled studies were noted within our search parameters.

Physical therapy

Physical therapy (PT) is one of the more popular, nonsurgical treatment choices. PT treatments begin by frequent, daily stretching of the muscles that could contribute to TOS, like the pectoralis minor, scalenes, and the other muscles of the neck and shoulder [6, 12, 20, 24, 31], [32], [33], [34], [35], [36], [37], [38], [39]. PT also consists of modifications to daily activities to keep symptom exacerbation at a minimum [24]. Some suggest avoiding provocative activities and arm positions, instead proposing PT programs that strengthen muscles of the pectoral girdle and help restore normal posture [40]. Postural correction and nerve glides are also utilized to provide some relief to patients [31, 35, 41, 42].

PT to strengthen weakened shoulder girdle muscles can be incorporated into the treatment plan [12, 32, 37, 39, 41], [42], [43], but is not always found to be effective, as muscle hypertrophy can contribute to further compression of the structures causing TOS symptoms [20]. In athletes, Warrick and Davis note that PT is a core component of conservative treatment for nTOS [44]. They report that activity modification is needed to limit repetitive overhead movement, with the evaluation of posture, biomechanics, and individual patterns of muscle use and tendon shortening as the focus of therapy [44].

Osteopathic manipulative medicine

OMT is another option for patients presenting with TOS; however, the literature search for TOS and OMT or osteopathic manipulation was limited, resulting in just four manuscripts and two case studies. Techniques such as high-velocity/low-amplitude, muscle energy, counterstrain, myofascial release, and the Still technique can all correct dysfunctions that are present and contributing to the TOS symptoms [45, 46].

Injections

Several articles describe the use of local anesthetics injected directly into the scalene or pectoralis minor muscles as both a diagnostic and therapeutic modality utilized specifically for nTOS [9, 15, 44]. The theory behind these injections is that these areas are common sites for compression of the brachial plexus, and the alleviation of pain utilizing these injections identifies the site of compression while potentially relieving symptoms [15].

Trigger point injections

Trigger point injections may offer relief to patients presenting with trigger point pain patterns or hypertonic muscles contributing to the compression of thoracic outlet neurovascular structures [31, 47].

Botulism injections

Botulism injections can be utilized to treat nTOS due to muscle hypertonicity. Patients whose compression is due to other causes, such as cervical rib or fibrous bands, are unlikely to respond to botulinum toxin (BoNT [Botox]) injections [48]. Botulinum injections into the scalenes may be recommended [30, 39]; however, Povlsen and Povlsen [49] concluded that there is moderate evidence to suggest that Botox injections into the scalene muscles have no benefit over placebo for improvement in pain or disability, although they may improve paresthesias in the long term in people with TOS of any type.

Ultrasound-guided deep nerve hydrodissection

Although not specific to nTOS, Lam et al. [50] reported efficacy of ultrasound-guided deep nerve hydrodissection of the stellate ganglion, brachial plexus, cervical nerve roots, and paravertebral spaces utilizing D5W as an alternative management in patients (n=26, 50% female) with complex regional pain syndrome with favorable results. Pain reduction 5 min after the last injection was 97.0% ± 6.9% in cases of acute pain and 87.7% ± 9.8% in cases of chronic pain (p=0.04) [50]. The mean improvement in the Numeric Pain Rating Scale (NPRS) at the 2-month posttreatment follow-up was 5.8 ± 1.9 points for cases of acute pain (8.0 ± 1.3 to 2.2 ± 0.7) and 6.5 ± 1.7 points for cases of chronic pain (p=0.385) [50].

Acupuncture

Hwang et al. [43] looked at traditional medicine approaches to the treatment of TOS and suggest that acupuncture has been reported to alleviate pain by the rebalancing of energy (Qi) and blood circulation in the meridians in diseases with multifactorial etiology, with positive effects on patients with TOS.

The authors would like to emphasize again that PT and OMT, as well as the other conservative therapies discussed, should not be attempted in suspected vTOS or aTOS when there are signs or symptoms of venous occlusion or limb ischemia until proper evaluation is completed.

Pharmacological treatments

Pharmacological treatments can be utilized in conjunction with the therapies described above or as standalone treatments. nTOS patients can take medications and receive nerve blocks and corticosteroids (either systemically or locally injected) to help decrease pain symptoms [6, 19, 24, 33, 37, 38, 41, 42, 51, 52]. Analgesics (nonsteroidal anti-inflammatory drugs [NSAIDs] or opioids) have been suggested for neuropathic pain, while muscle relaxants, anticonvulsants, and/or antidepressants as adjuvant have also been suggested [43].

Patients with vTOS are often treated with anticoagulation therapy and thrombolysis [34, 36, 53, 54]. Lee et al. [55] reported outcomes in 64 patients with vTOS utilizing a treatment protocol of catheter-directed thrombolysis, anticoagulation, and decompression and resection of the first rib in those patients with persistent symptoms as follows. A total of 29 patients (45.0%) required first rib resection within the first 3 months postthrombolysis; of the 35 patients (55%) treated successfully with thrombolysis and anticoagulation, 8 (23.0%) developed a recurrent thrombotic event in the same extremity (mean follow-up 13 months) and required further intervention, whereas the remaining 27 (77.0%) remained symptom-free after a mean follow-up of 55 months.

Due to symptoms of limb ischemia and the potential for significant tissue necrosis, most treatments for aTOS are surgical, with the only preoperative intervention being a catheter-directed thrombolysis [30, 56]. In general, when considering the options for all forms of vTOS, anticoagulation alone is generally not recommended and the combination of thrombolysis, decompressive surgery, and anticoagulation has a better prognosis and overall outcome for these patients [54, 55].

Surgical interventions for thoracic outlet syndrome

Surgery is the ultimate treatment recommended if conservative interventions fail to improve nTOS or if the patient presents with a vascular form of TOS requiring immediate decompression [54, 57], [58], [59]. Surgery for the decompression of TOS can be accomplished in several ways. The two main approaches are through the axillary or supraclavicular regions. If the etiology for compression is hypertrophied scalene muscles or a cervical rib, then the supraclavicular decompression is utilized, which involves exploration of the supraclavicular brachial plexus, neurolysis, removal of fibrotic bands, scalenectomy, primary first rib resection, and overlooked cervical ribs [60]. Complication rates reported for this procedure are relatively low; however, the data are limited by the sample size and a lack of randomized control studies.

If the site of compression is closer to the axilla, which happens when the pectoralis minor attachment to the coracoid process pulls down on the branches of the brachial plexus, then the transaxillary incision is preferred [20]. The transaxillary approach is also utilized to treat TOS patients with a compression at the first rib or cervical rib.

Surgery for nTOS is recommended only after more conservative measures, such as OMT and PT, have failed to improve symptoms or when the patient begins to develop significant disability [61].