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Thoracic Outlet Syndrome (TOS)

Middle aged man getting occupational therapy for upper extremity.

What is thoracic outlet syndrome?

Thoracic outlet syndrome (TOS) is a syndrome that can cause any combination of pain, weakness, numbness, tingling, sensation of coldness or, sometimes, a more general feeling of discomfort in portions of the upper body. It commonly affects in one or both of the upper limbs (arms) and/or the hands, armpits, upper back, neck and pectoral area of the chest.

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" through which blood vessels and nerves pass before they enter the arms to supply them with circulation (blood and oxygen) and sensation (pain and feeling) .

What causes thoracic outlet syndrome?

TOS is caused by compression of arteries and/or veins (called "vascular thoracic outlet syndrome"), the nerves between the shoulder and neck, known as the brachial plexus (called "neurogenic thoracic outlet syndrome") or a combination of the two.

The underlying cause of the compression itself can vary. It may be the result of an extra rib (known as a cervical rib), hypertrophic (enlarged) muscle or scar tissue, or abnormality of muscles in the neck. It can also occur from a 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 the glenohumeral joint of the shoulder can also create tension or traction on the nerves or blood vessels in the thoracic outlet region. Body position (such as poor posture or certain overhead activities) can also play a role in causing or contributing to symptoms.

What are the signs and symptoms of thoracic outlet syndrome? 

Thoracic outlet syndrome can lead to a wide range of symptoms. The classic, most common symptoms are pain, numbness, and tingling that radiates below the shoulder down towards the hand and usually into the pinky and ring finger. If compression involves the vascular structures, you may even see skin discoloration (paleness, bluishness, or even redness) in addition to a cold sensation.

If compression involves the nerves (brachial plexus), you may experience symptoms of a brachial plexopathy. This can include numbness, weakness (usually in the hand muscles), muscle wasting and muscle atrophy. You may also experience a loss of dexterity and fine motor skills.

How is thoracic outlet syndrome diagnosed?

As with most clinical disorders, a diagnosis of TOS should be based largely on the clinical symptoms a patient experiences and the physical exam by a doctor. Imaging tests – such as X-rays, MRIs, MRAs (magnetic resonance angiograms), MRVs (magnetic resonance venograms), MRNs (magnetic resonance neurograms) – and electrodiagnostic tests may help your doctor make the diagnosis, but they should be used only as adjuncts to the clinical assessment. In other words, your doctor should order such tests only to help confirm the suspected diagnosis or, in some cases, to objectively assess the functioning of your veins, arteries or nerves.

Making a diagnosis can sometimes be fairly straightforward, but more often it is difficult and elusive. This is because symptoms and their severity can vary widely. There is also some controversy within the field of medicine regarding the diagnosis and treatment of this condition, particularly around vascular TOS.

  • 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 by your doctor with the use of specialized electrodiagnostic tests called electromyography (EMG). A diagnosis for this condition is usually confirmed when an EMG test objectively demonstrates a patient's neurological deficits.
  • Vascular thoracic outlet syndrome is more controversial. Some doctors even dispute that it exists. It is more difficult to objectively demonstrate.
  • A third TOS category exists where patients may experience vascular or neurological symptoms, or even simply pain, but where neurological and vascular testing return generally normal results. This can be a very difficult diagnosis to make.

How is thoracic outlet syndrome treated?

The treatment of thoracic outlet syndrome is usually nonsurgical and is directed at treating the underlying causes and contributing factors. Chiefly, this involves activity and posture modification and special exercises under the guidance of a physical therapist.

  • Making changes to your posture, such as by postural exercises and ergonomic modifications may help significantly. The exercises usually focus on:
    • Stretching the pectorals or "pecs" (the muscles of the frontal chest wall)
    • Strengthening the shoulder retractors (rhomboids and trapezius muscles)
    • Improving head and neck alignment.
  • Chin retractions and corner/doorway stretches are also recommended. These are performed by placing the forearm (wrist to elbow) upward on both sides of a doorway (or, when facing a corner, on both sides of the wall). You then lean forward until a stretch is felt in the front of the shoulder joint. This position 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 in overweight patients is helpful to alleviate compression.
  • 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 listed above is usually a better first-line approach.

What is the surgery for thoracic outlet syndrome?

Surgery should be considered only after conservative measures have been tried but without relieving symptoms or when there is a risk for loss of neurological or vascular function. Possible surgeries include:

  • Removal of taut bands or scar tissue
  • Splitting of or removal of abnormal muscles
  • Removal of a cervical rib or a first thoracic rib
  • Surgical stabilization of an unstable shoulder

Some of these procedures have greater risks than others, you and your doctor should carefully assess and weigh the risks against the potential benefits. 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.

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