There are a number of types of thoracic outlet syndrome, including:

• Neurogenic (neurological) thoracic outlet syndrome. This form of thoracic outlet syndrome is characterized by compression of the brachial plexus. The brachial plexus is a network of nerves that come from your spinal cord and control muscle movements and sensation in your shoulder, arm and hand. In the majority of thoracic outlet syndrome cases, the symptoms are neurogenic.
• Vascular thoracic outlet syndrome. This type of thoracic outlet syndrome occurs when one or more of the veins (venous thoracic outlet syndrome) or arteries (arterial thoracic outlet syndrome) under the collarbone (clavicle) are compressed.
• Nonspecific-type thoracic outlet syndrome. This type is also called disputed thoracic outlet syndrome. Some doctors don't believe it exists, while others say it's a common disorder. People with nonspecific-type thoracic outlet syndrome have chronic pain in the area of the thoracic outlet that worsens with activity, but a specific cause of the pain can't be determined.

Thoracic outlet syndrome symptoms can vary, depending on which structures are compressed. When nerves are compressed, signs and symptoms of neurological thoracic outlet syndrome include:

• Muscle wasting in the fleshy base of your thumb (Gilliatt-Sumner hand)
• Numbness or tingling in your arm or fingers
• Pain or aches in your neck, shoulder or hand
• Weakening grip

Signs and symptoms of vascular thoracic outlet syndrome can include:

• Discoloration of your hand (bluish color)
• Arm pain and swelling, possibly due to blood clots
• Blood clot in veins or arteries in the upper area of your body
• Lack of color (pallor) in one or more of your fingers or your entire hand
• Weak or no pulse in the affected arm
• Cold fingers, hands or arms
• Arm fatigue with activity
• Numbness or tingling in your fingers
• Weakness of arm or neck

Throbbing lump near your collarbone

In general, the cause of thoracic outlet syndrome is compression of the nerves or blood vessels in the thoracic outlet, just under your collarbone (clavicle). The cause of the compression varies and can include:

• Anatomical defects. Inherited defects that are present at birth (congenital) may include an extra rib located above the first rib (cervical rib) or an abnormally tight fibrous band connecting your spine to your rib.
• Poor posture. Drooping your shoulders or holding your head in a forward position can cause compression in the thoracic outlet area.
• Trauma. A traumatic event, such as a car accident, can cause internal changes that then compress the nerves in the thoracic outlet. The onset of symptoms related to a traumatic accident often is delayed.
• Repetitive activity. Doing the same thing repeatedly can, over time, wear on your body's tissue. You may notice symptoms of thoracic outlet syndrome if your job requires you to repeat a movement continuously, such as typing on a computer, working on an assembly line or lifting things above your head, as you would if you were stocking shelves. Athletes, such as baseball pitchers and swimmers, also can develop thoracic outlet syndrome from years of repetitive movements.
• Pressure on your joints. Obesity can put an undue amount of stress on your joints, as can carrying around an oversized bag or backpack.
• Pregnancy. Because joints loosen during pregnancy, signs of thoracic outlet syndrome may first appear while you're pregnant.

There are several risk factors that seem to increase the risk of thoracic outlet syndrome, including:

• Sex. Females are far more likely to be diagnosed with thoracic outlet syndrome than are males.
• Age. Thoracic outlet syndrome is more common in young adults, between 20 and 40 years old.

If your symptoms haven't been treated early, you may experience progressive nerve damage, and you may need surgery. Doctors recommend surgery to treat thoracic outlet syndrome only when other treatments haven't been effective. Surgery has higher risks than do other treatments and may not always treat your symptoms.