Thoracic outlet syndrome (TOS) causes pain in the arm, shoulder, and neck. It happens when the nerves or blood vessels just below your neck are compressed, or squeezed. The compression can happen 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 is more common in women. It usually starts between 20 and 50 years of age. Doctors do nerve and imaging studies to diagnose it.

There are many causes of TOS, including

• Injury
• Anatomical defects
• Tumors that press on nerves
• Poor posture that causes nerve compression
• Pregnancy
• Repetitive arm and shoulder movements and activity, such as from playing certain sports

Treatment depends on what caused your TOS. Medicines, physical therapy, and relaxation might help. Surgery may also be an option. Most people recover.

NIH: National Institute of Neurological Disorders and Stroke