What is thoracic outlet syndrome (TOS)?

Diana Meeks
Diana Meeks on behalf of Sigma Nursing
Family Practitioner

The thoracic outlet is the area between the neck and chest. When a blood vessel or nerve is compressed in this area, it is known as thoracic outlet syndrome. Thoracic outlet syndrome refers to a group of disorders in this area.

Thoracic outlet syndrome (TOS) is a condition in which the nerves and/or blood vessels (neurovascular bundle) exiting from the neck becomes constricted or pinched resulting in numbness or decreased blood flow to the arm and hand. The specific structures involved in this condition can include brachial plexus nerves, subclavian artery/vein and phrenic nerve. These structures become entrapped between the collar bone (clavicle), 1st rib and the muscles of the neck known as the anterior and middle scalene muscle. If left untreated, TOS can result in severe paralysis, pain and disability. In extreme cases, surgical intervention may need to be performed to take out (resect) part of the collar bon or rib or release the scalene muscles in order to relieve the pressure of the structures involved.

Donna Hill Howes, RN
Family Practitioner

TOS is an umbrella term that encompasses three related syndromes that involve compression of the nerves, arteries and veins in the lower neck and upper chest area and cause pain in the arm, shoulder and neck. Most doctors agree that TOS is caused by compression of the brachial plexus or subclavian vessels as they pass through narrow passageways leading from the base of the neck to the armpit and arm, but there is considerable disagreement about its diagnosis and treatment. Making the diagnosis of TOS even more difficult is that a number of disorders feature symptoms similar to those of TOS, including rotator cuff injuries, cervical disc disorders, fibromyalgia, multiple sclerosis, complex regional pain syndrome and tumors of the syrinx or spinal cord. The disorder can sometimes be diagnosed in a physical exam by tenderness in the supraclavicular area, weakness and/or a "pins and needles" feeling when elevating the hands, weakness in the fifth ("little") finger and paleness in the palm of one or both hands when the individual raises them above the shoulders, with the fingers pointing to the ceiling. Symptoms of TOS vary depending on the type.

Neurogenic TOS has a characteristic sign, called the Gilliatt-Sumner hand, in which there is severe wasting in the fleshy base of the thumb. Other symptoms include paresthesias (pins and needles sensation or numbness) in the fingers and hand, change in hand color, hand coldness or dull aching pain in the neck, shoulder and armpit.

Venous TOS features pallor, a weak or absent pulse in the affected arm, which also may be cool to the touch and appear paler than the unaffected arm. Symptoms may include numbness, tingling, aching, swelling of the extremity and fingers, and weakness of the neck or arm.

Arterial TOS most prominently features change in color and cold sensitivity in the hands and fingers, swelling, heaviness, paresthesias and poor blood circulation in the arms, hands and fingers.

There are many causes of TOS, including physical trauma, anatomical defects, tumors that press on nerves, poor posture that causes nerve compression, pregnancy and repetitive arm and shoulder movements and activity, such as from playing certain sports.

TOS is more common in women. The onset of symptoms usually occurs between 20 and 50 years of age. Doctors usually recommend nerve conduction studies, electromyography or imaging studies to confirm or rule out a diagnosis of TOS.

Thoracic outlet syndrome (TOS) is the term is used to describe symptoms arising from compression of either the subclavian artery that supplies blood to the head and arms, and passes beneath the clavicle (arterial TOS), the subclavian vein (venous TOS) or brachial plexus, a group of spinal nerves emerging from the neck and leading into the arms (neurogenic TOS).

Thoracic outlet syndrome develops when the blood vessels and nerves that pass through the narrow passageway at the base of the neck to the armpit and arm (the brachial plexus or subclavian vessels) become compressed as a result of poor posture or anatomic abnormalities. The affected arm becomes pale and cool, and tingles, aches or feels numb. The pulse is weak or absent.

Risk factors include poor posture, obesity, weak shoulder muscles, injury and activities in which a person repeatedly raises or holds his or her arms overhead can all play a role in the development of thoracic outlet syndrome. In some cases no cause can be identified.

Dr. Rick Sayegh
Dr. Rick Sayegh on behalf of MDLIVE

Thoracic outlet syndrome (TOS) is a term used to denote a variety of upper extremity syndromes, with only a small number having a neurologic basis. TOS is generally divided into true neurogenic TOS, true vascular TOS (with arterial vascular and venous vascular subtypes), and disputed neurogenic TOS.

Thoracic outlet syndrome is a condition caused by compression of the blood vessels and nerves passing through the thoracic outlet.

Dr. Joshua I. Greenberg, MD
Vascular Surgeon

Thoracic outlet syndrome (TOS) is a condition caused by compression of the neurovascular structures (blood vessels and nerves) leading to the arm passing through the thoracic outlet (space between your collarbone and your first rib).

It affects approximately 0.3 to 2 percent of the general population.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.