Three neurovascular syndromes are associated with a rudimentary cervical rib (rarely with a complete cervical rib) and related abnormalities at the thoracic outlet: subclavian venous or arterial compression and a brachial plexopathy. In all three forms, shoulder and arm pain is prominent. The discomfort is of the aching type and is felt in the posterior hemithorax, pectoral region, and upper arm. These syndromes sometimes coexist, but more often each occurs independently.
Compression or spontaneous thrombosis of the subclavian vein is a rare occurrence causing a dusky discoloration, venous distention, and edema of the arm. The vein may become thrombosed after prolonged exercise (Paget-Schrötter syndrome) or in cases of a clotting diathesis in cancer patients.
Compression of the subclavian artery, which results in ischemia of the limb, may be complicated by digital gangrene and retrograde embolization, also is a rare entity. A unilateral Raynaud phenomenon, brittle nails, and ulceration of the fingertips are important diagnostic findings. A supraclavicular bruit is suggestive but not in itself diagnostic of subclavian artery compression.
The conventional tests for vascular compression—obliteration of the pulse when the patient, seated and with the arm extended, takes and holds a full breath, tilts the head back, and turns it to the affected side (Adson test) or abducts and externally rotates the arm and braces the shoulders and turns the head to either side (Wright maneuver)—are not entirely reliable. Sometimes these maneuvers fail to obliterate the radial pulse in cases of proved compression; contrariwise, these tests may be positive in normal persons. Nevertheless, a positive test only on the symptomatic side (with reproduction of the patient’s symptoms) is suggestive of the diagnosis of arterial compression and, by implication, some form of thoracic outlet syndrome. Plethysmographic recording of the radial pulse and ultrasound of the vessel add greatly to the accuracy of these positional tests.
A primarily neurologic problem may characterize the thoracic outlet syndrome. There is slight wasting and weakness of the hypothenar, interosseous, adductor pollicis, and deep flexor muscles of the fourth and fifth fingers (i.e., the muscles innervated by the lower trunk of the brachial plexus and ulnar nerve). Weakness of the flexor muscles of the forearm may be present in advanced cases. Tendon reflexes are usually preserved. In addition, most patients complain of an intermittent aching of the arm, particularly of the ulnar side, and about half of them complain also of numbness and tingling along the ulnar border of the forearm and hand. A loss of superficial sensation in these areas is variable. It may be possible to reproduce the sensory symptoms by firm pressure just above the clavicle or by traction on the arm. Vascular features are often absent or minimal in patients with the neurologic form of the syndrome.
In patients with neurologic signs, nerve conduction studies disclose reduced amplitude of the ulnar sensory potentials. There may be decreased amplitude of the median motor evoked potentials as well, a mild but uniform slowing of the median motor conduction velocity, and a prolongation of the F-wave latency. Concentric needle examination of affected hand muscles reveals large-amplitude motor units, suggesting collateral reinnervation. Somatosensory evoked potentials may be a useful adjunct to the conventional nerve conduction and EMG studies (Yiannikas and Walsh). Brachial artery MR angiography is usually reserved for patients with a suspected arterial occlusion, an aneurysm, or an obvious cervical rib. The place of venography in the diagnostic workup is uncertain, for a number of otherwise normal individuals can occlude the subclavian vein by fully abducting the arm.