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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.