Introduction to Thoracic Outlet Syndrome

Types of Thoracic Outlet Syndrome

There are several types of thoracic outlet syndrome (TOS), including:

  • Neurogenic TOS
  • Vascular TOS
  • Neurovascular TOS

Neurogenic Thoracic Outlet Syndrome

True Neurogenic Thoracic Outlet Syndrome

True neurogenic TOS is also called "called neurologic TOS" and is a rare disorder caused by congenital (birth) anomalies (cervical rib and band syndrome). It usually affects one side of the body and predominantly occurs in women ages 15 to 60 years. Symptoms include:

  • Weakness
  • Intermittent aching, numbness, and paresthesia (burning or tingling sensation) which may also involve the fourth and fifth fingers or arm
  • Wasting of the hand primarily involving the thenar muscles. Hand muscle atrophy is usually associated with this type of TOS.

True neurogenic TOS may often be confused with carpal tunnel syndrome.

Disputed Thoracic Outlet Syndrome

This category of thoracic outlet syndrome is by far the most common type seen by doctors. The term disputed TOS (also know as "non-specific TOS") was applied to this disorder because its existence is controversial. While some experts believe that it is a "real" disorder and occurs frequently, others have argued that it does not exist as a true clinical entity. The most prominent symptoms of disputed TOS are pain, paresthesia, and weakness (up to 95% of patients) however, extensive clinical examination often fails to detect any objective evidence of an underlying problem or cause. Several theories have been proposed regarding the etiology (underlying cause) of disputed TOS including trauma to the brachial plexus, congenital anomalies, or postural abnormalities.

Disputed thoracic outlet syndrome can present either as:

  • Upper plexus TOS which involves the cervical nerve roots (C5, C6, or C7)
  • Lower plexus TOS which involves cervical and thoracic nerve roots (C8-T1).

Vascular Thoracic Outlet Syndrome

Vascular TOS involves compression of the subclavian artery or vein. Patients are often young with a history of strenuous work or vigorous arm activity. There are two types of vascular thoracic outlet syndrome:

  • Arterial TOS
  • Venous TOS
Arterial Thoracic Outlet Syndrome

Arterial TOS accounts for less than 5% of cases of thoracic outlet syndrome and typically results from long-term, intermittent vascular compression. It is thought that chronic, episodic compression of the artery leads to:

  • Damage to the inner arterial wall. This can result ultimately in stenosis (narrowing) of the artery
  • Thrombus (formation of a clot)
  • Complications from thromboembolism (the thrombus detaches from its source and travels through blood vessels, potentially blocking the circulation of blood)

The majority of cases of arterial TOS arise due to congenital anomalies including:

  • Cervical ribs at the point of fusion with thoracic ribs
  • Fibrous bands arising off an incomplete cervical rib
  • Elongated transverse process of a vertebrae
  • Anomaly in the union of bones following fracture of the clavicle or first rib

Patients with arterial TOS are often younger than patients with neurogenic TOS and have a history of vigorous arm activity. The symptoms may initially be ignored since they are often mild (e.g., aching arm or fatigue after exercise). Early arterial compression is asymptomatic and is typically recognized only when it is more chronic and has lead to changes in the arterial wall.

The first sign of pathology is usually stenosis (narrowing) of the subclavian artery. The stenosis may spontaneously recede following a surgical procedure called thoracic outlet decompression. If the artery continues to be compressed, causing long standing inflammation, the artery may become fibrotic (tissue takes on fibrous quality). This could result in the formation of emboli, ranging from mild to severe. Ischemic (lack of oxygen) events occur usually due to distal emboli (in the arm or hand) or proximal (close to the thoracic outlet) arterial thrombosis (e.g., absent pulses, gangrene, symptoms of Raynaud's phenomenon)

Venous Thoracic Outlet Syndrome

Vascular TOS which involves the subclavian vein is also known as Paget-Schroetter Syndrome. It can be caused by thrombosis (formation of a clot attached to the wall of the vein) or it could be of a nonthrombotic origin.

There are two types of venous thoracic outlet syndrome:

  • Primary Venous TOS

    This is caused by a congenital narrowing of space in the part of the thoracic outlet where the subclavian vein passes through and may be caused by:

    • an anomalous first rib
    • long transverse process of the cervical spine
    • cervical ribs
    • hypertrophic (overgrown) scalene muscle which may develop in athletes whose muscles hypertrophy (enlarge from heavy lifting) and may cause compression of the subclavian vein.

  • Secondary Venous TOS

    This is caused by stenosis or thrombosis for known reasons, (e.g. a central line catheter inserted into the subclavian vein for treatment or placement of a pacemaker). The wall of the subclavian vein may be damaged during:

    • placement of a central line catheter
    • the infusion of medications
    • incorrect catheter placement.

Venous TOS typically occurs in young men. When it is related to overexertion, patients usually experience pain, swelling and/or cyanosis. Veins in the neck, shoulder, or front of the chest may be distended and the symptoms will intensify with increased activity of the involved arm.

Some patients develop Paget-Schroetter Syndrome which is a condition where a thrombus (clot) develops in the subclavian vein (beneath the collarbone) which results in pain, swelling, blue discoloration, and congestion of the arm. It is most commonly caused by compression of the vein between the collarbone and the first rib, and is considered one of the venous manifestations of thoracic outlet syndrome. It can be caused by primary (congenital anomaly) or secondary TOS and is associated with strenuous activity or unusual positioning of the arm. Approximately 15% of patients with subclavian vein thrombosis demonstrate some degree of occlusion (blockage) in the unaffected arm. A minority of patients spontaneously form collateral veins around the point of occlusion or the obstruction resolves. In the remainder of patients, immediate treatment is necessary.

Neurovascular Thoracic Outlet Syndrome

Neurovascular TOS usually follows trauma or injury. The most common type of trauma involves a fracture of the clavicle (collar bone) which may also cause secondary injury to the nerves and blood vessels within the thoracic outlet. Traumatic TOS usually develops on the same side where the injury occurred. The most frequent symptom is pain in the neck/shoulder area which may be accompanied by weakness and/or numbness in the arm/hand.