Presentation and course
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• Typical symptoms and signs of true neurogenic thoracic outlet syndrome include sensory symptoms over the medial hand or forearm and intrinsic hand muscle weakness and atrophy, disproportionately involving the thenar eminence; motor signs predominate.
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• Disputed thoracic outlet syndrome is best considered a cervicoscapular pain syndrome.
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• Arterial thoracic outlet syndrome often coexists with neurogenic thoracic outlet syndrome, and symptoms relate to limb ischemia.
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• Venous thoracic outlet syndrome results from thrombosis of the axillosubclavian vein; at-risk individuals include athletes and persons with hypercoagulable states.
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• The medial cord of the brachial plexus passes behind the midshaft of the clavicle and is highly susceptible to injury.
True neurogenic thoracic outlet syndrome. True neurogenic thoracic outlet syndrome will usually present with unilateral symptoms and signs, often initiated with pain. True neurogenic thoracic outlet syndrome has clear and well-accepted clinical and electrophysiologic features, reflecting involvement of T1>C8 sensory and motor fibers. The motor abnormalities are usually more pronounced and may be quite advanced at presentation because of the indolent progression of this disorder. Patients present with intrinsic hand muscle weakness, loss of dexterity, and wasting, primarily of the median-innervated thenar muscles, which are innervated primarily by T1>C8 axons (28). Weakness is present but less pronounced in ulnar-innervated hand and forearm muscles and least in radial-innervated forearm muscles. Sensory features in the form of pain, paresthesias, or numbness are usually present and involve the medial forearm or hand (28); they can, however, be subtle and require a careful sensory exam to demonstrate a deficit. This clinical phenotype has also been referred to as the Gilliatt-Sumner hand (07).
Disputed thoracic outlet syndrome. Best considered as a cervicoscapular pain syndrome, as suggested by Ferrante and Ferrante, this is the most common form of thoracic outlet syndrome and also the most nonspecific (04; 05). This is a highly controversial disorder that frequently frustrates clinicians and leads to disputes in the literature. The most prominent symptom is pain but it may also present with weakness, fatigue, or sensory loss. A lower plexus and an upper plexus pain pattern is described. The neurologic exam is typically unremarkable. Bilateral features are common compared to the other subtypes of thoracic outlet syndrome. Proponents of disputed thoracic outlet syndrome espouse the utility of provocative maneuvers such as the Adson, Wright, costoclavicular, and elevated arm stress test maneuvers, but these suffer from high false positive rates; an exhaustive discussion of this topic is presented by Ferrante and Ferrante (04; 05).
Arterial thoracic outlet syndrome. Arterial thoracic outlet syndrome is a rare condition, but the most devastating of all the thoracic outlet syndromes, and is caused by intermittent or prolonged arterial compression of the subclavian artery, typically by a cervical rib (10). Other etiologies include bony anomalies of the first thoracic rib, scalene muscle hypertrophy, or intramuscular fibrous bands (04; 05). It affects both males and females and is often found in young adults. Symptoms relate to limb ischemia and may include claudication, hypersensitivity to cold in the hands, and numbness or pain in the fingers. Uncommonly, arterial thrombosis may occur abruptly and distal emboli can result in finger ulcers or embolic ischemic strokes (18). Association between embolic stroke and arterial thoracic outlet syndrome was first described by Symonds in 1927 (27). Arterial thoracic outlet syndrome often coexists with neurogenic thoracic outlet syndrome (10).
Venous thoracic outlet syndrome. Venous thoracic outlet syndrome refers to the compression and thrombosis of the axillosubclavian vein and is frequently referred to as Paget-Schroetter syndrome or “effort thrombosis”. At risk individuals include athletes, especially weight lifters, baseball pitchers, and swimmers, which forms the basis of the term “effort thrombosis” (15). Persons with hypercoagulable states are also predisposed to develop this condition (11). An occlusive thrombosis may result in limb edema, cyanosis, congested veins, and pain. This disorder affects men more often than women, often unilaterally, involving the dominant limb.
Traumatic neurovascular thoracic outlet syndrome. This syndrome follows clavicular fracture and its presentation depends on the specific neurovascular elements involved in the injury, either directly through compression or laceration or indirectly through an expanding hematoma or aneurysm. Pain at the site of trauma often radiates down the arm. The medial cord of the brachial plexus passes behind midshaft of the clavicle and is highly susceptible to injury. Accordingly, sensory deficits may involve the distributions of the medial brachial, medial antebrachial, and ulnar nerves. Motor axons for the C8 and T1 roots are affected without clear predilection for T1>C8 involvement as seen in true neurogenic thoracic outlet syndrome. Furthermore, C8 radial motor axons are spared as they cross over to the posterior cord proximal to the lesion site.
A 42-year-old right-handed woman presented for another opinion regarding a diagnosis of “monomelic amyotrophy” of the right arm made 8 years previously. There was a long indolent history of at least 10 years of progressive right-hand weakness, atrophy, and loss of dexterity, though she managed to compensate and function well at work. She did not recall ever having significant pain or numbness but did have a vague discomfort in the medial forearm. Examination revealed severe right thenar atrophy and abductor pollicis brevis weakness, mild ulnar intrinsic atrophy and weakness, and mild weakness of finger extension. Reflexes were normal. There was reduced pinprick and touch sensation over the medial forearm. The left arm and legs were normal.
Nerve conduction studies in the right arm revealed an absent medial antebrachial cutaneous sensory nerve action potential, reduced ulnar sensory amplitude, normal median sensory potential, severely reduced median compound muscle action potential amplitude, and mildly reduced ulnar motor amplitude. Comparable studies on the left arm were normal. EMG showed reduced recruitment of polyphasic, large-amplitude, long duration, rapidly firing motor unit potentials in the abductor pollicis brevis, first dorsal interosseous, abductor digiti minimi, and extensor indicis muscles; the abductor pollicis brevis muscle also had few fibrillations. The study was consistent with a lower trunk brachial plexopathy and the clinical syndrome consistent with true neurogenic thoracic outlet syndrome. Plain films and cervical CT showed a right cervical rib at C7. Routine MRI failed to reveal a fibrous band or other anomaly. Surgical exploration with resection of the cervical rib and likely fibrous band was offered but the patient declined due to concern about possible complications and given her high level of function without pain.