THORACIC OUTLET SYNDROMESThoracic outlet syndromes include those disorders that result in compression of the neurovascular structures supplying the upper extremity. Among them are cervical rib syndrome, costoclavicular syndrome, scalenus anticus and scalenus medius syndromes, pectoralis minor syndrome, "effort thrombosis" of the axillary and subclavian veins, and the subclavian steal syndrome. Patients often have a history of trauma to the head and neck areas. Symptoms and signs may arise from intermittent or continuous pressure on elements of the brachial plexus and the subclavian or axillary vessels by a variety of anatomic structures of the shoulder girdle region. The neurovascular bundle can be compressed between the anterior or middle scalene muscles and a normal first thoracic rib or a cervical rib. Descent of the shoulder girdle may continue during adulthood and cause compression. Faulty posture, chronic illness, and occupation may be other predisposing factors. The components of the median nerve that encircle the axillary artery may cause compression and vascular symptoms. Sudden or repetitive strenuous physical activity may initiate "effort thrombosis" of the axillary or subclavian vein. Pain may radiate from the point of compression to the base of the neck, the axilla, the shoulder girdle region, arm, forearm, and hand. Paresthesias are frequently present and are commonly distributed to the volar aspect of the fourth and fifth digits. Sensory symptoms may be aggravated at night or by prolonged use of the extremities. Weakness and muscle atrophy are the principal motor abnormalities. Vascular symptoms consist of arterial ischemia characterized by pallor of the fingers on elevation of the extremity, sensitivity to cold, and, rarely, gangrene of the digits or venous obstruction marked by edema, cyanosis, and engorgement. Deep reflexes are usually not altered. When the site of compression is between the upper rib and clavicle, partial obliteration of subclavian artery pulsation may be demonstrated by abduction of the arm to a right angle with the elbow simultaneously flexed and rotated externally at the shoulder so that the entire extremity lies in the coronal plane. Neck or arm position has no effect on the diminished pulse, which remains constant in the subclavian steal syndrome. Radiographic examination is helpful in differential diagnosis. Plethysmography as an objective method of recording brachial arterial pulsations has been emphasized. When venous or arterial obstruction is intra-vascular, venography or arteriography demonstrates the location of the occlusion. Determinations of the conduction velocities of the ulnar and other peripheral nerves of the upper extremity may help to localize the site of their compression. Thoracic outlet syndrome must be differentiated from symptomatic osteoarthritis of the cervical spine, tumors of the cervical spinal cord or nerve roots, periarthritis of the shoulder, and other cervicobrachial pain syndromes. Conservative treatment is directed toward relief of compression of the neurovascular bundle. The patient is instructed to avoid physical activities likely to precipitate or aggravate symptoms. Overhead pulley exercises are useful to improve posture. Shoulder bracing, although uncomfortable, provides a constant stimulus to improve posture. When lying down, the shoulder girdle should be bolstered by arranging pillows in an inverted "V" position. Symptoms may disappear spontaneously or may be relieved by conservative treatment. Operative treatment is more likely to relieve the neurologic rather than the vascular component that causes symptoms. |
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