What is thoracic outlet syndrome (TOS)?
The TOS, which is often difficult to diagnose, can occur from either vascular (5% of cases) or neurologic compression (95% of cases). It can be static or positional. TOS is most likely to occur in patients who have had trauma (clavicular fracture), repetitive strain injury (poor ergonomics at desk worksite), sports-related activities (overhead sports, baseball pitchers, swimmers, volleyball, etc.), or anatomic abnormalities (cervical rib, Pancoast tumor). Vasogenic TOS occurs when occlusion of the subclavian artery results in ischemic symptoms, or when venous occlusion results in edema, engorged superficial veins, and thrombosis (Paget–Schroetter disease). Neurogenic TOS occurs when there is brachial plexus impingement from a cervical rib (35%), fibrous tissue bands, scalene muscles, or an elongated transverse process of C7. This results in weakness of the intrinsic muscles of the hand along with sensory loss in the ulnar distribution over the hand and forearm.
The Adson maneuver is performed with the patient in a sitting position by palpating the radial pulse while the patient inhales deeply and extends the neck, turning the head to the side being examined (cervical rib) and then turned away from the side being examined (scalenus anticus syndrome). A positive Adson maneuver occurs when there is diminution of the radial pulse and reproduction of symptoms. Another provocation test, the hyperabduction maneuver (“hands up test”), is performed with the shoulder placed in abduction and external rotation to 90 degrees, elbows flexed at 45 degrees, and palms facing forward for 1 minute to determine if this causes unilateral TOS symptoms, indicating pectoralis minor impingement. If this does not cause symptoms, then the test is repeated with the patient’s arm hyperabducted to 180 degrees and extended to see if that causes unilateral symptoms due to costoclavicular compression of the neurovascular bundle. The costoclavicular maneuver is performed by the patient assuming an exaggerated military posture with shoulders back and downward. This positioning causes compression between the clavicle and first rib (may be positive in patients with a history of clavicular fracture). Note that in TOS, electrodiagnostic studies are usually normal and many normal people have false-positive physical examination provocation tests (especially decreased pulse). Treatment consists of range of motion and strengthening exercises to improve posture, avoidance of hyperabduction, botulinum toxin injections, and surgery for those patients with severe, refractory symptoms (cervical rib or fibrous band resection).