What Is Thoracic Outlet Syndrome (TOS)?


Thoracic outlet syndrome (TOS) is a condition in which the nerves and/or blood vessels in the thoracic outlet become compressed, irritated or injured. The thoracic outlet is a narrow space located between the collarbone and the first rib. The nerves and blood vessels that move down the arm, and the muscles from the neck to the shoulder, run through the thoracic outlet.

Types of thoracic outlet syndrome

The three types of thoracic outlet syndrome include neurogenic, venous and arterial. It is possible for multiple parts of the thoracic outlet to become compressed or a mix of all three types of TOS to occur. The symptoms help determine the type of TOS.

  • Neurogenic thoracic outlet syndrome affects nerves and is the most common type of TOS. It involves compression of the brachial plexus, which is a network of nerves in the shoulder that supply sensation and movement of the arms and hands.
  • Venous thoracic outlet syndrome affects veins and occurs due to compression or damage to one or more of the major veins under the clavicle (collarbone). It usually develops quickly and results in the formation of a blood clot.
  • Arterial thoracic outlet syndrome affects arteries and is the least common, yet most serious, type. It occurs due to abnormalities in the upper chest and neck area. Compression of an artery under the collarbone often results in an aneurysm.

Symptoms of thoracic outlet syndrome

TOS pain may be confused with angina; however, pain caused by TOS does not increase when walking, while angina pain typically does. Additionally, angina pain does not increase due to raising the affected arm, but TOS pain does.

Thoracic outlet syndrome symptoms vary depending on the type.

Symptoms of neurogenic TOS include:

  • Numbness or tingling in the arm or fingers
  • Pain in the neck, shoulder, arm or hand
  • Weakened grip

Symptoms of venous TOS include:

  • Discoloration of the hand or finger(s)
  • Pain and swelling of the arm
  • Blood clots in a vein in the upper body area
  • Arm fatigue with activity
  • Throbbing lump near the collarbone

Symptoms of arterial TOS include:

  • Cold hands, fingers or arms
  • Arm and hand pain
  • Lack of color or bluish discoloration in the hand or finger(s)
  • Weakened pulse in the affected arm

Causes of thoracic outlet syndrome

Although a specific cause is not always detected, TOS can be caused by any condition that enlarges tissue near the thoracic outlet. Causes include, but are not limited to, the following:

  • Injury or traumatic event, such as a vehicle crash
  • Weight gain
  • Weight lifting or significant muscle enlargement in the neck or chest area
  • Birth defects, such as an extra rib extending from the neck or a tight fibrous band that connects the spine to the rib
  • Poor posture, such as drooping the shoulder or head forward
  • Obesity
  • Tumor in the chest area
  • Collarbone fracture that reduces space for nerves and blood vessels
  • Sleep disorders
  • Sports or occupations involving repetitive arm or shoulder movement
  • Whiplash injury
  • Soft tissue abnormalities

Although rare, a tumor at the top of the lung can also result in TOS.

Risk Factors

The risk of developing TOS is increased for the following:

  • Sex. Females are at greater risk than males.
  • Age. Adults between the ages of 20 and 50 have an increased risk.
  • Occupation. Those that often perform upper extremity resistance, such as jack-hammer operators, dental hygienists, etc., are at higher risk.
  • Pregnancy. The risk of developing TOS is greater when pregnant.
  • Weight. Obesity increases the risk of TOS.
  • Athletes. Participating in sports that require repetitive arm or shoulder motions, such as baseball, swimming, golf, volleyball, etc., heightens the risk.
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