Pathogenesis is often unknown but sometimes involves compression of the lower trunk of the brachial plexus (and perhaps the subclavian vessels) as these structures traverse the thoracic outlet below the scalene muscles and over the 1st rib, before they enter the axilla, but this involvement is unclear. Compression may be caused by
Thoracic outlet syndromes are more common among women and usually develop between age 35 and 55.
Pain and paresthesias usually begin in the neck or shoulder and extend to the medial aspect of the arm and hand and sometimes to the adjacent anterior chest wall. Many patients have mild to moderate sensory impairment in the C8 to T1 distribution on the painful side; a few have prominent vascular-autonomic changes in the hand (eg, cyanosis, swelling). In even fewer, the entire affected hand is weak.
Rare complications of thoracic outlet compression syndromes include Raynaud syndrome localized to the affected arm and distal gangrene.
A diagnosis of a thoracic outlet compression syndrome is suggested by distribution of symptoms. Various maneuvers are alleged to demonstrate compression of vascular structures (eg, by extending the brachial plexus, as by abducting the extremity to bring it overhead), but sensitivity and specificity are poor. Auscultating bruits at the clavicle or apex of the axilla or finding a cervical rib by x-ray can aid in diagnosis.
Although angiography may detect kinking or partial obstruction of axillary arteries or veins, neither finding is incontrovertible evidence of disease.
Electrodiagnostic testing is warranted in all patients with suggestive symptoms, and MRI of the brachial plexus, cervical spine, or both is usually also necessary.
Most patients who have a thoracic outlet compression syndrome without objective neurologic deficits respond to physical therapy, nonsteroidal anti-inflammatory drugs, and low-dose tricyclic antidepressants.
If cervical ribs or subclavian artery compression is identified, an experienced specialist should decide whether surgery is necessary. With few exceptions, surgery should be reserved for patients who have significant or progressive neurovascular deficits and do not respond to conservative treatment.
Consider thoracic outlet syndromes if patients have unexplained pain and paresthesias that begin in the neck or shoulder and extend down the medial arm.
Do electrodiagnostic tests and usually MRI of the brachial plexus and/or cervical spine.
Treat most patients with analgesics and physical therapy.
Consider surgery if patients have a cervical rib or subclavian artery compression and neurovascular deficits that progress despite conservative treatments.