Thoracic Outlet Syndrome (TOS): An Overview

[MJ note 2/4/19: This content was edited and moved to the TOS condition list page, which was bereft of content.]


Thoracic Outlet Syndrome (TOS) is a syndrome that can cause any combination of pain, weakness, numbness, tingling, a cold sensation, or sometimes a more general type of discomfort in one or both upper limbs. This can be the result of compression of the vascular structures (arteries and/or veins), neurological structures (nerves between the shoulder and neck, known as the brachial plexus), or involvement of both the vascular and neurological structures.

The term “thoracic outlet” comes from its location in the body. The area above and behind the clavicle (collarbone), from the neck to the shoulder, forms an outlet that the nerves and blood vessels in this region pass through before entering and supplying the arm with sensation and circulation.


Thoracic Outlet Syndrome can vary widely in the range of symptoms it can cause. While some patients may have minimal discomfort or loss of function, others may be more symptomatic. Similarly, the diagnosis can at times be relatively straightforward but is often more difficult and elusive. 

As with most clinical disorders, the diagnosis should be highly suspected based on the clinical symptoms and the physical exam. Additional tests such as plain X-rays, MRIs, MRAs (MR angiograms), MRVs (MR venograms), and electrodiagnostic tests may help make the diagnosis but they should be used as adjuncts to the clinical assessment. They are ordered when needed to confirm the diagnosis or to objectively assess vascular or neurological function.

The classic and common symptoms are pain, numbness, and tingling that radiates below the shoulder down towards the hand and usually into the pinky and ring finger. When compression involves the vascular structures, patients may even see skin discoloration (paleness, bluishness, or even redness) in addition to a cold sensation.

When compression involves the nerves (brachial plexus), patients may experience symptoms of a brachial plexopathy. This could include numbness, weakness (usually in the hand muscles), muscle wasting, and muscle atrophy. This may also lead to loss of dexterity and fine motor skills.


The cause of Thoracic Outlet Syndrome is usually a compression of some sort. This can vary and be the result of an extra rib (known as a cervical rib), hypertrophic (enlarged) muscle/scar tissue, or anomalous (abnormal) muscles in the neck. It can also occur from narrowing of the thoracic outlet space between the clavicle and chest wall or in the region where the nerves and blood vessels pass under muscles as they cross the shoulder.

Hypermobility (looseness) of the either of the scapula (shoulder blade) or glenohumeral joint (shoulder instability) may also create tension or traction on the neurovascular structures in the thoracic outlet region and lead to thoracic outlet-type symptoms. Body position can also play a role in causing or contributing symptoms. Examples of this are poor posture and certain overhead activities.

Diagnosis and Treatment

There is some controversy about the diagnosis and treatment of Thoracic Outlet Syndrome.

Neurogenic thoracic outlet syndrome (TOS involving the neurological structures) leads to weakness and muscle atrophy in addition to pain. In this condition, there are usually neurological deficits that can be objectively identified with specialized testing (EMGs). An abnormal electrodiagnostic test (EMG) demonstrating objective neurological deficits is the basis for diagnosing neurogenic TOS.

Vascular thoracic outlet syndrome is more controversial - even disputed by some clinicians - and more difficult to objectively demonstrate. A third category also exists; these patients may experience vascular, neurological, or just painful symptoms, but because neurological and vascular testing is generally normal, the diagnosis is more difficult to make.

Conservative Treatments

Treatment of TOS is usually directed at treating the underlying cause and contributing factors.

Postural changes, postural exercises, and ergonomic modifications should all be considered. Exercises are usually geared towards stretching the anterior (front) chest wall muscles (pectoral muscles), strengthening the shoulder retractors (rhomboids and trapezius muscles), and improving head and neck alignment.

Chin retractions and corner/doorway stretches are recommended. These are performed by placing the forearm (wrist to elbow) on both sides of a doorway or, when facing a corner, both sides of the wall. The rest of the body then leans forward as a stretch is felt in the front of the shoulder joint. This can be held anywhere from 20 to 30 seconds. Any exercise that causes pain or triggers off neurological or vascular symptoms should be discontinued.

Weight loss should be encouraged in patients with obesity. Oral medication such as anti-inflammatories ( aspirin, ibuprofen, naproxen) may provide some relief, but addressing mechanical symptoms with the right stretching, strengthening, and modifications of activities is usually a better first line approach.

Surgical Options

Surgery should be considered only after conservative measures have been exhausted unless there is a risk for loss or neurological or vascular function.

Surgical decisions should be made not only when conservative care has been ineffective but also after considering how reliable surgery is in correcting or restoring proper anatomy in the least invasive way.

Removal of taut bands or scar tissue, splitting or removal of anomalous muscles, removal of a cervical rib or a first thoracic rib, or surgical stabilization of an unstable shoulder are some of the surgical options that may be available, but because some of these procedures have greater risk than others, the risk-to-benefit probability should be carefully considered.




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