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Thoracic Outlet Syndrome

Paul F. Pasquina MD

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Synonyms
Scalenus anticus syndrome

Cervical rib syndrome

First thoracic rib syndrome

Costoclavicular syndrome

Subcoracoid-pectoralis minor syndrome

Hyperabduction syndrome[1]

ICD-9 Code
353.0
Brachial plexus lesions (cervical rib syndrome, costoclavicular syndrome, scalenus anticus syndrome, thoracic outlet syndrome)

Definition
Thoracic outlet syndrome (TOS) remains a contentious area in medicine. The term is used to describe a number of conditions attributed to a compromise of the brachial plexus (typically the lower trunk), subclavian/axillary artery or vein, or both at one or more points between the base of the neck and the axilla. Because of the controversy and confusion surrounding this entity it is helpful to further subclassify the condition based on the neurovascular structure that is compromised: neurologic (axonal) TOS, vascular TOS, and disputed/symptomatic TOS.[2]
Vascular TOS refers to compromise of the subclavian/axillary artery or vein. Both are very rare and usually affect young to middle-aged persons. Vascular compromise may develop from trauma, thrombi, or congenital anomalies, such as a fully formed cervical rib or abnormal first thoracic rib. Traumatic causes such as midclavicular fractures may present acutely or as a late effect secondary to non-union or excessive callus formation. Repetitive trauma has also been implicated, such as that seen in throwing sports. Intimal damage to vascular structures may lead to thrombus or aneurysm formation.
Neurologic (axonal) TOS refers to true compression of the brachial plexus with resultant axonal damage, particularly to the lower trunk. This condition is also very rare, affecting young to middle-aged women more than men. Although many conditions may contribute to brachial plexus injuries (e.g., trauma, tumor, infections), the term "neurologic TOS" is used to describe a condition believed to be caused by the compression of the distal T1 and, to a lesser extent, the distal C8 anterior primary rami, by a taut band that extends from a rudimentary cervical rib or elongated C7 transverse process to the first thoracic rib.
"Disputed," or "symptomatic," TOS refers to a condition that occurs more commonly than both the vascular and true neurologic types. It is defined more as a symptom complex rather than a true anatomic pathologic process. Because of the difficulties in defining this condition, accurate etiologic data is not available, although it appears to affect women more than men. It is a diagnosis of exclusion, and therefore other conditions must be excluded prior to making the diagnosis. Physical examination should reveal normal neurologic and vascular findings.

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 Figure 41-1 Areas of compression of the neurovascular bundle. A, Hypertrophy of scalene muscles. B, Presence of cervical rib. C, Presence of a fibrous band. D, Compression by pectoralis minor during hyperabduc tion. (From DePalma AF: Surgery of the Shoulder, 2nd ed. Philadelphia, J.B. Lippincott, 1973, pp 511–520, with permission.)
Symptoms
Patients typically report pain along the distal and ulnar aspects of their forearm and hand as well as sensory symptoms such as numbness, tingling, and burning. These symptoms are often aggravated by certain positions or activities, especially those involving overhead work. Subjective complaints of weakness or of dropping objects should be verified by physical examination. Those with vascular compromise may present with swelling, cyanosis, coldness, or even Raynaud's type symptoms.

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Physical Examination
Physical examination should include an extensive evaluation of the patient's neck, shoulders, and upper extremities, with particular attention to the neurologic and vascular examinations. The patient should be undressed in order to assess any postural abnormalities or side-to-side atrophy.
Careful attention to the neck range of motion and a positive Spurling's test may reveal a cervical root lesion. Abnormal reflexes, weakness, and atrophy are consistent with a true neurologic deficit. Neurologic TOS, affecting primarily the lower trunk of the brachial plexus, may reveal atrophy of the thenar greater than hypothenar eminence in the hand, weakness of the hand intrinsic muscles, and sensory abnormalities of the medial forearm and hand.
Patients with vascular compromise to their upper extremity may have upper extremity swelling, discoloration, prominent dilated veins, subungual hemorrhages, and ulcerations of the fingertips.[3] These patients may also have a diminished radial pulse, especially after exercise.
Patients with disputed/symptomatic TOS, as discussed earlier, have normal neurologic and vascular examinations. This, however, may be difficult to establish, especially if a patient reports nonspecific decreased sensation or weakness associated with pain or "give-way" effort. These patients often present with a "droopy shoulder" posture, characterized by a long thin neck, and sloping, rounded, and often protracted shoulders, with horizontal clavicles.[4] Some patients may have tenderness in the supraclavicular fossa overlying the anterior/middle scalenes.
Careful palpation to the scalene, trapezius, levator scapulae, or supraspinatus muscles may reveal identifiable trigger points, reproducing the patient's symptoms. This finding would be more consistent with a diagnosis of myofascial pain syndrome.
Special tests, such as a Tinel's sign at the elbow or wrist and a positive Phalen's maneuver, may be helpful when considering the diagnosis of cubital or carpal tunnel syndrome. Other special tests advocated in evaluating TOS, such as Adson's, Allen's, hyperabduction, and costoclavicular tests, have disputed results.
Functional Limitations
Patients with all forms of TOS typically have difficulty with upper extremity function, particularly when their arms are in the overhead or abducted positions. In addition, the patient may report difficulty carrying heavy objects, such as groceries, when a downward load is applied to the upper extremities causing additional stretch to the plexus and vessels.
Patients with more advanced disease may have significant weakness and numbness of the hands, impairing their ability to perform fine motor activities such as writing, typing, buttoning a shirt, and working a cash register.
TOS has been reported in a subsection of patients who are instrumental musicians. Patients most affected were reported to play the violin or viola, followed by keyboard instrumentalists and flutists.[5]
Diagnostic Studies
Cervical spine x-rays are helpful to identify an elongated C7 transverse process or a rudimentary cervical rib. In addition, oblique films of the cervical spine are helpful to evaluate for significant neuroforaminal stenosis, which may be more consistent with a cervical radiculopathy. If the clinician has a high suspicion of cervical radiculopathy, even in the face of normal cervical spine x-rays, magnetic resonance imaging (MRI) should be performed to rule out a possible herniated nucleus pulposus.
Chest x-rays or clavicular films may reveal a possible pancoast tumor or an undiagnosed clavicular fracture.

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Electrodiagnostic testing (e.g., EMG and nerve conduction studies) may be extremely helpful in determining the presence of true neurologic insult as well as localizing the injury to the root, plexus, or peripheral nerve (median or ulnar). Hallmark findings of neurologic (axonal) TOS include abnormal needle EMG activity in the C8/T1 myotomes as well as decreased amplitudes of the median greater than ulnar compound motor action potential (CMAP) and ulnar sensory nerve action potential (SNAP) with preservation of the median SNAP.[6] Abnormal ulnar motor conduction velocity studies across the "thoracic outlet" should be interpreted with skepticism, as these recordings have been shown to be of no use. [7] Normal electrodiagnostic testing is expected in both vascular and disputed/symptomatic TOS.
An MRI of the brachial plexus may be particularly helpful in identifying a possible soft tissue lesion, such as a tumor or hematoma, which may be compromising the plexus.
Arteriography and venography are indicated for further evaluation of possible vascular compromise; however, given the risk of potential complications from these more invasive procedures, they are typically done at the discretion of a vascular surgeon.
Differential Diagnosis
Cervical radiculopathy

Carpal tunnel syndrome

Traction plexopathy

Thrombophlebitis

Vasculitis

Myofascial pain syndrome

Neuralgic amyotrophy

Ulnar neuropathy

Mass lesion (tumor, hematoma)

Arteriosclerosis

Multiple sclerosis

Syringomyelia

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