If you have thoracic outlet syndrome (TOS), the nerves or blood vessels just below your neck are compressed, or squeezed. It can be between the muscles of your neck and shoulder or between the first rib and collarbone.
You may feel burning, tingling and numbness along your arm, hand, and fingers. If a nerve is compressed, you may also feel weakness in your hand. If a vein is compressed, your hand might be sensitive to cold, or turn pale or bluish. Your arm might swell and tire easily.
TOS can be a repetitive stress injury. An extra rib, scar tissue, traumatic injury or inherited defects can also cause TOS. Treatment depends on what caused your TOS.
NIH: National Institute of Neurological Disorders and Stroke