Thoracic outlet syndrome (TOS)

What is thoracic outlet syndrome (TOS)?

Thoracic outlet syndrome (TOS) is an umbrella term for conditions that involve the compression of neurovascular structures over the thoracic area i.e. from the lower neck to the armpit.

Each type of TOS is referred to by the structure that is being predominantly affected:

  • Neurogenic (nTOS) from brachial plexus compression - the most common type of TOS. The brachial plexus is a network of nerves that sends signals to your shoulder, arm and hand from the spinal cord
  • Venous (vTOS) from subclavian vein compression. The subclavian vein is one of the deep veins in your neck.
  • Arterial (aTOS) from subclavian artery compression. The subclavian arteries are two major arteries in the thorax that lie beneath each clavicle (collarbone).

Woman with hand on neck and thoracic area.


If left untreated, certain types of TOS can cause serious blood clots, nerve damage, permanent arm swelling and pain as well as gangrene from loss of blood flow.

Symptoms of TOS

Symptoms can vary depending on the type of TOS. They can also vary between individuals and be intermittent.

Neurogenic (nTOS) from brachial plexus compression:

  • Neck and arm pain
  • Numbness and tingling in the fingers
  • Wasting away of the hand muscles (atrophy)

Venous (vTOS) from subclavian vein compression:

  • Hand or arm pain
  • Cyanosis (a bluish or purplish skin discolouration)
  • Swelling of the arm on the affected side
  • An increased risk of thrombosis in the affected arm

Arterial (aTOS) from subclavian artery compression:

  • Mild arm ache
  • Arm fatigue
  • Pain
  • Pallor (an unhealthy, pale-looking appearance)
  • Feeling cold
  • Decrease of blood pressure in the arm

Medical tests to diagnose thoracic outlet syndrome

To exclude other possible conditions with overlapping symptoms and diagnose TOS, you may have an electromyography and imaging scans such as a chest x-ray or MRI (magnetic resonance imaging). You may also have:

  • CT (CAT) scan or MRI of the spine
  • An ultrasound
  • Cervical spine x-ray
  • Blood tests
  • Vascular studies (an examination of the arteries and veins)
  • Nerve conduction studies

What are the causes?

  • Traumatic injury
  • Tumours
  • A cervical rib
  • Repetitive motions of the area with raised arms such as in swimming, tennis, throwing, and carrying heavy objects over your head
  • Obesity

Can it be prevented?

Many cases of TOS cannot be prevented.

Treatments for thoracic outlet syndrome

Treatment depends on which structure is being compressed and the severity of the symptoms.

Neurogenic (nTOS) from brachial plexus compression:

  • Medications (e.g. pain relief, muscle relaxants)
  • Physical therapy
  • Surgery (if previous measures haven’t been effective).

Venous (vTOS) from subclavian vein compression:

  • Medications (e.g. thrombolytic medication to dissolve blood clots and anticoagulants, also known as blood thinners, which prevent clots.
  • Surgery

Arterial (aTOS) from subclavian artery compression:

  • Thrombolytic medication
  • Surgery

If surgery is necessary, you’ll be advised to avoid heavy lifting for some time and may receive physiotherapy.

Which type of specialist treats thoracic outlet syndrome?

If arteries and veins are affected, a vascular surgeon is the trained specialist who can surgically treat TOS. A thoracic surgeon, an expert in the chest, may also be required. If the nerves are affected, you may require a neurologist

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