Neurogenic TOS typically presents between the ages of 20 and 40 and affects women more often than men. Predisposing factors may be trauma or repetitive strain injury to the neck or upper extremity. In many cases, an anatomic abnormality is present and represents the underlying reason for the development of symptoms of TOS. Importantly, the mere presence of anomalous thoracic outlet anatomy does not correlate with the development of symptoms. More often than not, however, trauma or occupational influences superimposed on a pre-existing anatomic abnormality result in the actual development of clinical symptoms. Occupational repetitive strain injury to the brachial plexus may be caused by chronically performing tasks with arms extended or overhead. Persons who use a computer keyboard or mouse for long periods of time, mechanics, and painters are at increased risk for occupational repetitive strain injuries and for developing neurogenic TOS. Throwing athletes are also at risk for developing TOS due to repetitive overhead throwing motions.

Initial symptoms are pain and paresthesias in the neck, radiating into the affected upper extremity. Pain typically predominates the proximal regions, and paresthesias are present more distally. Sensory and motor deficits may develop in more advanced cases, but they are not required for diagnosis. In extreme cases muscle wasting and atrophy may be present. The lower trunk of the brachial plexus (C8 and T1) is commonly involved, and symptoms manifest in an ulnar distribution along the lateral forearm, last two digits, and lateral half of the middle digit. Upper brachial plexus (C5 to C7) involvement is somewhat less common and is characterized by paresthesias of the medial forearm, thumb, and index finger. Cervical and upperback pain are common, as are headaches. Raynaud syndrome may also accompany neurogenic symptoms. Symptoms are aggravated by overhead arm elevation, lifting, and activities involving repetitive motions, and they may be relieved during rest and inactivity.

Diagnosis is heavily weighted on the history and a physical examination employing provocative maneuvers to elicit symptoms. The diagnosis is largely one of exclusion, and diagnostic tests are used primarily for elimination of alternative diagnoses. A number of provocative tests that alter neck and shoulder position have been described, including: the Adson test (obliteration of the radial pulse during arm abduction with inspiration and the head turned away from the affected side); Roo’s test (reproduction of symptoms with rapid opening and closing of the hand with the arm 90 degrees abducted and the arm flexed 90 degrees at the elbow); and upper-limb tension test (reproduction of symptoms in the supine position with passive arm abduction and elbow and wrist extension). A positive Adson test with radial pulse obliteration during arm elevation suggests tightness within the interscalene or costoclavicular spaces, but it has poor diagnostic sensitivity and specificity in TOS and may be found in as many as 5% of normal individuals. Examination should also include a thorough evaluation for possible peripheral nerve entrapment at the carpal or cubital tunnels; it should also
include a thorough orthopedic examination of the neck and shoulder regions. Up to 50% of patients with may have additional evidence of distal nerve entrapment, such as carpal or cubital tunnel syndromes, due to a “double crush” mechanism. Plain radiographs of the chest and neck are normal in the majority of cases, but they may be useful for identifying bony anomalies such as cervical ribs, large C7 transverse process, or bony exostosis. Magnetic resonance imaging (MRI) and magentic resonance (MR) neurography are useful for evaluating the cervical nerve roots and brachial plexus, scalene muscles, and subclavian vessels. Deviation of the normal course and trajectory of the brachial plexus may suggest entrapment or impingement. MRI is, perhaps, most valuable for the exclusion of significant cervical spine pathology. Electrodiagnostic testing is inconsistently helpful and is frequently normal, but it may identify peripheral neuropathies in a minority of cases.

Like the other forms of TOS, arterial TOS most commonly presents in young adults between the ages of 15 and 40. Throwing athletes, such as baseball pitchers, are at increased risk due to muscular hypertrophy and repeated trauma to the artery during forceful arm abduction and rotation. In contrast to neurogenic TOS, underlying bony anomalies are the rule, not the exception, and cervical ribs or other bony anomalies are commonly identified in patients with arterial TOS. Other bony abnormalities associated with the development of arterial TOS include: articulated first ribs, large C7 transverse processes, or bony callus formation following a clavicle or rib fracture. Dynamic compression of the subclavian artery by anomalous structures during arm abduction or rotation is the underlying cause of arterial TOS. Chronic compressive trauma to the artery may result in stenosis and poststenotic dilatation, which eventually can progress to formation of a true subclavian artery aneurysm. Arterial ulceration, alone or associated with an aneurysm, may also develop as a consequence of repeated compression injury to the subclavian artery. Development of symptoms is most often due to distal embolization of thrombus from a subclavian artery aneurysm or ulcer, presenting clinically with digit pain, ulcerations, or gangrene. Occasionally, patients present with more profound upper-extremity ischemia due to acute subclavian artery thrombosis. Cases have also been reported of embolic stroke from retrograde embolization of subclavian artery thrombus into the right carotid or vertebral arteries.

Diagnosis of arterial TOS is based upon objective physical examination findings of distal thromboembolism and positional loss of the upper-extremity pulses with arm elevation and rotation (Adson test). Elevation of the subclavian artery pulse and the presence of a subclavian artery bruit also support the diagnosis. Plain radiographs can identify associated bony anomalies, such as cervical ribs. Duplex ultrasound studies can demonstrate a subclavian artery aneurysm or arterial narrowing with increased flow velocities during arm abduction. Magnetic resonance angiography (MRA) with arms adducted and abducted can also demonstrate subclavian artery compression and significant subclavian artery lesions. Contrast angiography, however, remains the gold standard and is often necessary to identify subtle arterial abnormalities and distal arterial occlusions due to thromboembolism. Angiography should be performed with the arms in both the adducted and abducted positions, and magnified views of the subclavian artery should be obtained.

Neurogenic TOS is best managed conservatively with an emphasis on physical therapy, correction of posture, rest, avoiding activities that precipitate symptoms, and ergonomic modification of the workplace. Up to 90% of patients will be successfully managed nonoperatively when an appropriate conservative regimen is followed. Surgery is generally reserved for patients with persistent symptoms and disability who have failed to improve significantly despite an extensive course of appropriate conservative treatment. Patients with positive electrodiagnostic testing or clinically apparent atrophy of the intrinsic hand muscles from a brachial plexopathy are an exception and should be treated early with surgery to avoid progressive loss of function. Psychosocial issues are commonplace, and neurogenic TOS is one of the most litigated surgical procedures; therefore, thorough informed consent and attention to psychiatric issues are imperative before proceeding with operation.