Pain Due to Thoracic Outlet Syndrome

Kaj Johansen

Thomas Tai Chung

George I. Thomas

An important and incompletely understood cause of upper extremity pain is subsumed under the rubric of “thoracic outlet syndrome” (TOS). This condition arises from compression of neurovascular structures as they enter/exit the neuraxis and the mediastinum at the base of the neck. Particularly in cases involving chronic compression of the brachial plexus, TOS can be a complicated and frustrating condition to manage due to ongoing controversy about the underlying pathophysiology, how the diagnosis is best made, and differing views about proper and effective treatment. Many of the problems regarding TOS revolve around the uncertain natural history of the condition with and without intervention. In this chapter, we discuss the various types of TOS with a particular emphasis on the neurogenic type—by far the most common, the most disputed, and also the most likely to result in pain.

Anatomy and Pathophysiology

The thoracic outlet is the aperture through which the subclavian artery and trunks of the brachial plexus pass as they exit the neuraxis and the upper mediastinum at the base of the neck. In normal anatomic circumstances, the thoracic outlet is bound by several musculotendinous and bony structures including the anterior and middle scalene muscles and, inferiorly, the first rib (Fig. 39.1). In pathologic circumstances, compression of the neurovascular bundle at the thoracic outlet is most commonly the consequence of abnormalities of the scalene muscles and/or the first rib. However, neurovascular compression can also result from the presence of a cervical rib, abnormal fibrous bands, callus from a clavicular fracture, scarring from prior trauma or radiation therapy, or (rarely) a superior sulcus (Pancoast) tumor of the lunch.

FIGURE 39.1 The anatomy of the normal thoracic outlet and abnormalities leading to thoracic outlet syndrome. A: Normal anatomy of the thoracic outlet. B: The presence of a first cervical rib can lead to compression of the subclavian artery and/or the brachial plexus (red shaded region) between the cervical rib and the clavicle. C: Hypertrophy of the anterior and middle scalene muscles following trauma can lead to compression (arrows) of the subclavian artery and/or the brachial plexus.

Because the subclavian vein lies anterior to the anterior scalene muscles, it does not actually pass through the thoracic outlet. It is, however, located between the clavicle and the first rib in its course toward the mediastinum.

In normal circumstances, arm elevation or abduction results in a functional reduction in the caliber of the thoracic outlet aperture because of posterior rotation of the clavicle and contraction of the scalene muscles. The space between the clavicle and the first rib narrows, and below the shoulder, the pectoralis minor muscle contracts.

Trauma, particularly cervical hyperextension (“whiplash”), or chronic repetitive use of the upper extremities (particularly in an out-front or overhead position), may, over time, result in chronic spasm, inflammation, and contracture of the scalene muscles, producing both the thickening of the anterior and middle scalene muscles as well as microstructural changes in muscle fiber type.¹^,²

Provocative maneuvers of the arm may result in compression of the subclavian artery and vein in up to 30% of normal
individuals.³ Reduction in the caliber of the thoracic outlet by pathophysiologic circumstances can result in extrinsic compression of the subclavian artery or vein in more than 90% of patients with TOS.

A cervical rib, abnormal bands, or residua from a clavicular fracture can result in subclavian artery dilation or even aneurysm or mural thrombus formation, from which embolization into the arterial circulation of the wrist or hand may occur.

Extrinsic compression of the subclavian vein in the costoclavicular space, perhaps involving the tendon of the subclavius muscle, can, in concert with repetitive use of the upper extremity, result in axillosubclavian venous thrombosis, likely due to intimal damage and venous stasis.

Clinical Presentation: Symptoms and Signs

Arterial TOS is extremely uncommon, comprising less than 1% of the totality of any TOS practice, and almost always presents as forearm or hand “claudication” (or other upper extremity ischemic symptoms) or evidence for distal upper extremity embolization. Physical examination demonstrates diminished or absent wrist pulses; vascular laboratory examination may show occlusion of the radial and/or ulnar arteries or their palmar or digital branches. On occasion, patients may present with rest pain or gangrene of the fingers due to far-advanced ischemia from repetitive distal arterial embolic occlusion.

Physical findings in patients with arterial TOS are primarily those of absent or diminished pulses and/or manifestations of distal upper extremity ischemia.

Involvement of the upper extremity venous circulation by compression of the subclavian vein at the thoracic outlet comprises approximately 5% of a TOS practice. Patients with such venous TOS (also termed Paget-Schroetter syndrome or “effort” thrombosis of the axillosubclavian vein) may present with aching pain distributed diffusely throughout a swollen, ruborous upper extremity. In more chronic circumstances, pain and swelling may be less prominent.

On exam, patients with acute venous TOS manifest arm swelling and discoloration; in later stages, prominent veins can be seen over the upper arm and around the shoulder.

By far the most common presentation—the overwhelming majority of the patients seen in a TOS practice—results from compression of elements of the brachial plexus, that is, neurogenic TOS. Patients with neurogenic TOS almost always have a prior traumatic event—a cervical hyperextension (“whiplash”) injury, a fall on an outstretched arm, an object falling on the head or the shoulder—or alternatively have a history for a repetitive stress injury, usually due to exigencies of their occupation. Workplace risk factors for neurogenic TOS include sustained effort with the upper extremity or extremities out-front or overhead and may be seen in drywall hangers, dental hygienists, beauticians or hairdressers, grocery checkers, shelf stockers, or clerical workers engaged in prolonged keyboarding.

Such injury or workplace-related postures and stresses have been demonstrated to result in chronic contracture and spasm of the suspensory muscles in and around the shoulder girdle—among them the anterior and middle scalene muscles. Obesity, sedentary lifestyles, and maladaptive postures—in neurogenic TOS, characterized by the head flexed on the neck and the shoulders down and forward—exacerbate chronic scalene muscle spasm.

Patients with neurogenic TOS may have few or no symptoms with the arms in a neutral position. However, they will quickly note the onset of pain and paresthesias with the arms placed in an out-front, overhead, or abducted posture. Indeed, this presentation is so stereotypic that we do not seriously entertain the diagnosis of neurogenic TOS in the absence of a subject’s observation of worsened symptoms with the arms in such provocative postures.

Symptoms characteristically evoked in neurogenic TOS patients include elevational arm aching, particularly proximally around the shoulder, the axilla, and the upper arm, associated variably with numbness and tingling out the arm, distal weakness, and a limitation in range of motion of the affected upper extremity. Paresthesias are found predominately in a lower trunk (C8-T1) distribution, appropriate to impingement on the lower aspects of the brachial plexus. Indeed, 80% of patients with neurogenic TOS demonstrate pain and paresthesias radiating along an ulnar nerve distribution, often into the small and ring finger as a consequence. This presumably results from upward traction on the first rib by the scalene muscles, thus selectively impacting the inferior aspects of the brachial plexus.

A significant proportion of patients with neurogenic TOS have significant headaches, primarily occipital.⁴ They also may note symptoms of facial or jaw pain or pain around ear. Muscle pain is commonplace in neurogenic TOS, particularly around the neck and the shoulder, the scapula, and the upper arm. It is frequently difficult to discern whether such symptoms arose from neurogenic TOS itself or from concurrent soft-tissue injuries (e.g., the paraspinous or periscapular muscles: the rotator cuff in the shoulder) suffered at the same time as the injury causing the neurogenic TOS.

Patients with neurogenic TOS frequently display a series of symptoms associated with activities of daily living which, in the aggregate, strongly indicate the presence of neurogenic TOS. Elements of our clinical template are shown in Table 39.1.

In neurogenic TOS, objective physical examination findings are sparse. Such individuals have limited range of motion of the affected upper extremity and manifest diminished spontaneous (adventitial) movements of the extremity as well as an unwillingness to place or maintain the affected limb in various provocative postures. Muscle tenderness over the anterior and lateral neck is commonplace, as is neck muscle tightness or contracture. In the supraclavicular fossa, tenderness can be elicited with palpation over the brachial plexus at the scalene triangle, often resulting in radiation of neuritic sensations into the axilla or out the arm (a positive Tinel sign). Occasionally, a cervical rib can be palpated. Tenderness over the pectoralis minor tendon attachment at the coracoid process below the shoulder is commonplace.

More peripherally in the upper extremity, tenderness may be elicited with palpation deep in the axilla. Tenderness of the arm or forearm muscles or tendons, or evidence for peripheral nerve compression at the carpal or cubital tunnels, may be present but is not, however, a primary manifestation of neurogenic TOS. Instead, this may represent the concurrent upper extremity injury that may accompany neurogenic TOS (“double crush” syndrome).⁵ Rarely, intrinsic hand muscle atrophy may be observed, a so-called Gilliatt-Sumner hand.⁶

A series of provocative tests are commonly performed which, individually or in the aggregate, are thought by many to demonstrate the presence of neurogenic TOS. The Adson test is carried out with the affected arm held downward and
backward: The ipsilateral wrist pulse is palpated as the head is turned toward this arm while the subject undertakes a sustained inspiration. A positive test, suggesting the presence of neurogenic TOS, results when the wrist pulse is obliterated.

TABLE 39.1 Clinical Elements that Suggest Neurogenic Thoracic Outlet Syndrome

Inability to drive with the hands elevated in the normal 10 o’clock/2 o’clock position on the steering wheel

Problems with grooming (shampooing the hair or use of a hairdryer)

Awakening at night with pain or numbness in the affected arm(s)

“Drop attacks”: the tendency to drop things, often without recognizing that grip strength has diminished

Inability to carry out sustained overhead activities, for example, changing multiple light bulbs in the ceiling

Loss of handwriting legibility (with involvement of the dominant upper extremity)

Inability to remove a tight jar lid

The military or shoulder brace position involves retraction of the shoulders backward and downward, which may result in pulse obliteration at the wrist.

The Roos or abduction/external rotation (AER) (“hands-up”) test involves, as described, the arms held at 90 degrees at the shoulders, the elbows flexed 90 degrees, and the hands then contracted repeatedly. A positive test involves rapid fatiguing and pain in the affected upper extremity.

Sanders and colleagues⁷ have reported the high positive and negative predictive value of the brachial plexus tension test. Here, the arms are held horizontally with the elbows and wrists straight and the neck is laterally flexed away from the affected arm: Both wrists are then extended. A positive test is characterized by a sense of tightness and pain in the ipsilateral neck as well as neuritic symptoms radiating out the affected arm.

Although not a provocative test for neurogenic TOS, the Spurling test is important in the evaluation of this condition. Because an important alternative diagnosis in these patients may be cervical radiculopathy, development of characteristic symptoms with lateral flexion of the neck toward the affected extremity makes neuroforaminal compression due to herniated disk, scar, or arthritis more probable and neurogenic TOS less likely.

The aforementioned provocative tests are commonly performed as part of an evaluation for neurogenic TOS. Skeptics point out that, although the sensitivity of each of these tests may be high, their specificity is very low (e.g., more than 30% of the asymptomatic population may have a positive Adson test).³ Similar results hold for the military (shoulder brace) position. The AER (“hands-up”) test has a high sensitivity and much better specificity for neurogenic TOS. Experienced clinicians’ view is that patients ultimately demonstrated to have neurogenic TOS will be strongly positive for many or most of these tests, individually or in the aggregate.

FIGURE 39.2 Computed tomography angiography with multiplanar reformatted images demonstrating compression of the subclavian artery between the insertions of the anterior and middle scalene muscles in a patient with a cervical rib. A: Coronal image demonstrating external compression of the subclavian artery as it passes cephalad to the cervical rib. B: Axial image demonstrating narrowing of the subclavian artery due to compression on the artery by the anterior scalene muscle. C: Sagittal, right paramedian image demonstrating compression of the subclavian artery as it passes between the insertion of the anterior and middle scalene muscles on the cervical rib. (Images courtesy of Dean Donahue, MD, Division of Thoracic Surgery, Massachusetts General Hospital, Boston, MA.)

Diagnostic Tests

In patients with arterial TOS, chest roentgenography will frequently confirm the presence of a cervical rib or callus from a clavicular fracture. A noninvasive vascular laboratory examination of the upper extremity will confirm the absence of (or reduction in) arterial flow at the hand and wrist level, not uncommonly in a pattern consistent with thromboembolic occlusion. Duplex scanning of the subclavian artery may demonstrate stenosis with poststenotic dilation or aneurysm formation with mural thrombus within. Computed tomography (CT) scan or catheter-directed arteriography may demonstrate sharp angulation of the subclavian artery over a cervical rib or around a clavicular fracture callus (Fig. 39.2); such imaging studies may also document the specific distribution of distal forearm, wrist, or hand arterial occlusions.

In venous TOS, noninvasive vascular laboratory examination will demonstrate partial or complete axillosubclavian venous thrombosis.⁸ Enlarged venous collaterals around the shoulder
may be displayed. Not uncommonly, upstream venous tributaries of the arm such as the basilic vein may demonstrate partial or complete thrombosis as well.

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