Thoracic Outlet Syndrome

Disease/ Disorder

Definition

Thoracic outlet syndrome (TOS) refers to a constellation of upper extremity symptoms from compression of neurovascular structures coursing through the thoracic inlet. Based on the principal site of compression or irritation, the disorder is classified as either true (classic) neurogenic TOS, vascular TOS, or nonspecific TOS.^{1,28, 29}

Etiology

TOS may result from compression or irritation of the brachial plexus, subclavian vein, subclavian artery, or a combination of the three.^1,28,29 Compression may occur from soft tissue mass or abnormal musculoligamentous and bony structures; these changes may be congenital, or they may be related to trauma, overuse, or neoplasm.^{28, 29, 33}

Epidemiology including risk factors and primary prevention

Accurate diagnosis and incidence of TOS is difficult due to the absence of consistently reproducible objective measures. Some authors propose an incidence of 3-80 cases per 1000.² Proportionately, neurogenic TOS (nTOS) is estimated to comprise over 90% of TOS. Venous TOS (vTOS) accounts for 3% and arterial TOS (aTOS) is estimated to have the lowest incidence, at less than 1%.⁴ The female/male ratio for nTOS is 3.5:1 and there is no sex predilection for aTOS or vTOS.^{5, 29} Studies indicate that vTOS affects a similar proportion of men and women.^{5, 29}

Studies indicate average range of development of nTOS is between teenage to 60 years of age.²⁸ Both vTOS and aTOS usually develop in young patients without significant comorbidities.⁵ The typical age range for the development of vTOS is between 20 to 30 years of age.²⁹

Patho-anatomy/physiology

TOS occurs secondary to compression of the subclavian artery, subclavian vein, or brachial plexus at the level of the thoracic inlet.^{1, 27-33} The thoracic inlet can be divided into three sections: the interscalene triangle, the costoclavicular triangle, and the subcoracoid/pectoralis minor space.^{2, 27-29} The neurovascular bundle can be compressed or irritated at any of these structures.  Compression most often occurs at the interscalene triangle.² Interscalene triangle surface area can be decreased by cervical ribs, fibrous bands, and kyphotic musculoskeletal anatomy.² Fibrous bands are more likely than rib anomalies to cause constrictions.^2,7,8 Cervical ribs are a rarity; most are asymptomatic.⁴ Anomalous bands may arise from cervical or rudimentary first thoracic rib, C7 vertebra, subpleural membrane, or scalene muscles.² Repetitive trauma to the neurovascular bundle at the thoracic inlet may lead to TOS, with the lower trunk or medial cord of the brachial plexus most affected.¹ Functional thoracic outlet syndrome has been associated in case reports with postural deviation, including increased kyphosis exacerbating compression at the thoracic inlet. Repetitive shoulder use and above-shoulder athletic endeavors (swimming, throwing) may increase injury risk^{6, 27-29}. Nonspecific thoracic outlet syndrome may be seen secondary to kyphotic posture, tight pectoralis muscles and latissimus dorsi.

Classic syndromes have been defined as follows:

Scalenus Anticus Syndrome: compression of subclavian artery or brachial plexus at interscalene triangle.^27,28

Costoclavicular Syndrome: compression of subclavian artery, subclavian vein, or brachial plexus between first thoracic rib and clavicle.^27,28

Hyperabduction Syndrome: compression of the subclavian or axillary artery, or brachial plexus between the pectoralis minor tendon. ^27,28

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

Natural History

nTOS can cause lasting nerve damage if left untreated, resulting in atrophy, pain and paresthesias. ^27,28

vTOS can lead to complications including arm swelling, pain, ischemic ulceration, gangrene, and thromboembolic events.^{4, 27,28}

aTOS can lead to mural thrombus formation, embolization, aneurysm degeneration of subclavian artery due to pressure build up from decreased flow, and limb-threatening ischemia.^{27, 28}

Clinical Presentation

It is important to evaluate for mimics of TOS in diagnostic phase.  Differential diagnosis includes C8-T1 radiculopathy, brachial plexopathy, carpal tunnel syndrome, ulnar neuropathy, intrinsic shoulder pathology, and myofascial pain.

Essentials of Assessment

History

Arterial TOS: Symptoms include limb coldness, pallor, arm fatigue, and claudication with exercise and arm elevation.^7,27 Thismay be accompanied by numbness, tingling, altered temperature sensation, and delayed capillary refill of the affected limb. ²⁷   

Venous TOS: Symptoms include swelling, edema, cyanosis, and exercise-induced limb pain. Patients may present with subclavian vein thrombosis; sudden onset of limb edema, dusky cyanosis, and pain.⁷

Neurogenic TOS: Symptoms include arm pain and paresthesias; cervical and shoulder symptoms. nTOS may present with painless hand muscle atrophy, weakness of grip strength due to hand intrinsic muscle wasting, and paresthesias.⁸ Occipital headaches were present in 76% of patients.²⁸ Symptoms are worse with activities that involve overloading, such as picking up an object on a high shelf or involving pronounced limb extension.²⁹ Symptoms can also be reproduced with direct palpation of the supraclavicular or infraclavicular space, depending on the site of compression of the brachial plexus.²⁷ With nTOS, symptoms are initially mild and intermittent, increasing in frequency and severity with time.⁷

Physical examination

• Perform a comprehensive exam for all patients, evaluating for motor weakness and vascular compromise.
• Examine upper extremities for differences in color, temperature, moisture, atrophy, edema, fingernails, and hirsutism.
• Test distal pulses with hands resting upon patient’s lap. Alteration of the radial pulse was thought to be pathognomonic for scalenus anticus syndrome, however, specificity is low (18-87%).^7,10,11
• Venous TOS: patient may present with cyanotic upper extremity. Superficial veins dilated in the upper arm, neck, and chest.²⁹
• Neurogenic TOS: pain on palpation above the brachial plexus, trapezius and scalene muscles, anterior chest wall but not pathognomonic of syndrome.²⁹

Special Tests for Thoracic Outlet Syndrome

The current provocative special tests used to diagnose TOS have low specificity and thus, high false positive rates.⁹

• Wright’s test: monitor the radial pulse with the arm in 90 degrees of abduction/external rotation, head neutral or rotated to opposite direction. Damping or loss of pulse may corroborate diagnosis of vascular TOS (positive in 7% of normal).⁷
• Adson’s maneuver: Radial pulse palpated at wrist with patient seated, forearms on knees, take long breath, elevating the chin and turning the head ipsilaterally. In the modified version, radial pulse palpated at wrist with the shoulder abducted 30 degrees, arm maximally extended, and head turned ipsilaterally. The test is positive if there is marked decrease or disappearance of radial pulse ²⁹. This test is nonspecific.^{9, 29}
• Roos test:  It is also known as Elevated Arm Stress Test (EAST Test). It is performed with the patient’s arm at 90-degree abduction/external rotation, shoulder and elbow in frontal plane. The patient opens and closes hands in slow repetitive motion for 3 minutes. The test is positive if symptoms are reproduced including gradual pain in the neck and shoulder, progressing down the arm, with paresthesias in the forearm and digits. If arterial compression, arm pallor with extremity elevated and reactive hyperemia as limb is lowered.^{7, 27} Specificity of Roos test is very poor.^{9, 27}
• Elvey’s Maneuver: It is also known as Upper Limb Tension Test (ULTT). Abducting shoulder to 90 degrees, contralateral rotation of the head, and wrist extension. It checks for the presence of nerve compression in the thoracic outlet and may trigger paresthesia and pain. It has low sensitivity and specificity.^{27, 29}

Functional assessment

Evaluation of grip strength, finger abduction strength, and repetitive above shoulder activity is important in assessing level of impairment in ADLs.

Laboratory studies

EDX studies to distinguish between cervical radiculopathy, peripheral mono- or poly- neuropathies, from nTOS.¹²

Typical EDX findings in neurologic TOS:

• Nerve conduction studies (NCS)
  • Median motor NCS: reduced CMAP amplitude, normal latency
  • Median sensory NCS: normal
  • Ulnar motor NCS: +/- reduced CMAP amplitude, normal latency
  • Ulnar sensory NCS: reduced SNAP amplitude, normal latency
  • MABC sensory NCS: reduced/absent CMAP amplitude
• Needle EMG
  • Fibrillations/positive waves, reduced recruitment, neurogenic MUAPs: especially in abductor pollicis brevis, also ulnar innervated hand muscles, other C8-T1 innervated muscles in severe cases.

EDX studies for patients with neurogenic TOS can be normal. This is possibly due to extreme proximity of brachial plexus compressing, making it difficult to get accurate EMG reading. Furthermore, EMG is not sensitive in detecting early and less severe nTOS because nerve compression is intermittent and positional. More severe nTOS with permanent nerve damage is detected by EMG. ^{34, 35}

Imaging

The goal of imaging is to localize the site of compression and evaluate the compressing structure and the compressed structure. Comparing arms down with hyperabduction is an essential part of any testing modality. Cervical spine radiographs or MRI may be performed to rule out extra rib, axial disease, cervical radiculopathy, bony abnormalities, or neoplasm. Ultrasound is often used in the initial evaluation of patients with suspected vascular TOS and can be helpful as is noninvasive and can be performed with provocative maneuvers, however cannot adequately assess the plexus or evaluate deeper pathology.^{13, 27,28,30} The optimal exam for evaluation of vascular TOS is contrast-enhanced MRI/MRA with provocative arm positioning. Non-contrast MRI with arm in abduction can be sufficient to diagnose nTOS.¹³ The advantage of MRI over CTA or CT alone is that it provides information on both vascular flow and characterizes surrounding soft tissue and bony structures without radiation exposure. However, asymptomatic patients may have abnormal testing, therefore imaging should be used as a confirmatory test based on clinical suspicion.^{5,14,28, 30}

Supplemental assessment tools

The Visual Analog Scale is useful for pain assessment. SF-36 and other functional assessment forms characterize functioning and track treatment success/failure.

Early predictions of outcomes

Persistent pain, weakness that does not improve despite 6 months of conservative management, or lack of improvement on EMG findings correlate with poorer prognosis with nonsurgical management and are indications for surgical intervention in cases of underlying anatomic compression.^{6, 27}

Environmental

Repetitive shoulder use and above-shoulder athletic (swimming, throwing) and work endeavors may increase injury risk. Workplace ergonomic modifications may be useful in cases where prolonged poor posture may lead to functional impairments. ²⁷

Social role and social support system

Rehabilitation of TOS may require significant changes to ADLs and work life. Evaluation by a pain psychologist may be beneficial.  If hand intrinsic muscle strength and abduction strength is lost, upper extremity work capacity may be significantly impaired.

Professional Issues

Professional/work life may be impaired in due to weakness and pain. Modification of work duties may be indicated in certain cases.

Rehabilitation Management and Treatments

Available or current treatment guidelines

Goals of treatment are to prevent disability, manage ischemia, initiate appropriate anticoagulation or thrombolysis, and adequately manage pain.

Rehabilitation

The most common course of treatment for acute and subacute TOS is conservative management including behavioral modification, limitation of provocative activities (i.e. arm positions), and a customized course of physical therapy. Targeted physical therapy entails strengthening exercises of the pectoral girdle and postural training, improvement of scapular kinematics to counteract thoracic kyphosis.^{2,15, 27,28} Other physical treatments include nerve gliding, mobilization of the first rib, and muscle energy treatments are used but have limited supporting evidence.¹⁶ Workplace ergonomic modifications may be useful in cases where prolonged poor posture may lead to functional impairments. ³¹

Chemodenervation

Chemodenervation of the scalenes, pectoralis minor, and subclavius muscles with botulinum toxin has been used as a treatment for symptoms predominantly in nTOS, using various methods of guidance (ultrasound, EMG, CT).^17-19 Case reports and case series suggest improvement in pain control and blood flow, however this has not been confirmed in a double-blinded, placebo-controlled study.²⁰ The use of botulinum toxin has fallen out of favor due to lack of durable benefits.²⁷

Surgery

When acute or subacute progressive neurologic weakness occurs secondary to nTOS, surgical decompression should be considered.³   Guidelines are not established in cases in which pain is the only manifesting symptom. The surgical approach is determined by the major site of compression. First rib resection with scalenectomy is the most common operation of choice for surgical decompression.²⁸ Emergent surgery indicated in cases of severe vascular occlusion or acute embolism to ensure revascularization.² Surgical decompression for vTOS and nTOS has shown mixed outcomes in quality of life measures, with some positive outcomes for short term but mixed results for long term outcomes and are dependent on patient selection.^{21-30, 32} Immediate post-surgery rehabilitation is important to optimize recovery^.27

At different disease stages

As noted above, the most common course of treatment for acute and subacute nTOS is conservative management including behavioral modification, limitation of provocative activities, and physical therapy for at least 4-6 months. ²⁷ NSAIDS, opioids, and muscle relaxants are used for symptomatic relief. ^{27, 28} If there is progressive or severe neurologic deficit (i.e. weakness), then surgery may be considered.

If symptoms are refractory to conservative care or in chronic TOS, then chemodenervation can be considered. Surgery is considered in chronic nTOS with progressive weakness.

For vTOS and aTOS complicated with thrombosis, the initial treatment is anticoagulation with intravenous heparin to stabilize clot and prevent propagation. Catheter directed venography/ arteriography should be used next to clear clot and restore flow to subclavian vein/ artery. Symptoms refractory to catheterization may require surgery^{. 28}

Coordination of care

Good communication between physicians, therapists, radiologists, and surgeons is essential to the appropriate care of patients.

Patient & family education

Effective communication of disease etiology and prognosis along with work/life implications and modifications is always indicated.

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

The key to appropriate management is distinguishing nTOS, vTOS, and aTOS, as they have different treatment approaches. Intrinsic shoulder injury, cervical radiculopathy, poly- or mono-neuropathy, and other neuropathic syndromes must be ruled out as mimickers of TOS.

Electrodiagnostic testing may be helpful to distinguish nTOS from aTOS and vTOS.However, EDX has low specificity and high false positive rates. EDX can be normal for patients with nTOS. EDX can also rule out other neurologic causes. ^{28, 30, 34, 35}

MRI/MRA with provocative arm positions is the optimal imaging test for evaluation of TOS. ^{28, 30}

Nonspecific TOS also known as disputed TOS, without objective imaging or electrodiagnostic findings, is controversial.³⁶

Cutting Edge/ Emerging and Unique Concepts and Practice

For the evaluation of vascular TOS, contrast-enhanced MRI/MRA with provocative arm positioning best assess vascular flow. Non-contrast MRI with arm in abduction can be sufficient to diagnose nTOS.^{13, 28, 30} The advantage of MRI over CTA or CT alone is that it provides information on both vascular flow and characterizes surrounding soft tissue and bony structures without radiation exposure. ^{28, 30}

Gaps in the Evidence-Based Knowledge

A major gap in evidence-based knowledge is the absence of an objective grading system for TOS upon which consensus for diagnosis and indications for treatment can be made. Some clinicians believe that surgical intervention is overused and that the diagnosis of TOS itself is controversial and not fully accepted.

References

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Original Version of the Topic

Clark C. Smith, MD, Raj Telhan, MD. Thoracic Outlet Syndrome. 2/05/2013.

Previous Revision(s) of the Topic

Philip A. Nelson, MD and Carley Sauter, MD. Thoracic Outlet Syndrome. 4/5/2017.

Author Disclosure

Laura Gruber, MD
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Deepthi Ganta, MD
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Rohini Singh, DO
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Vincent Lee, DO
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