Thoracic outlet syndrome is a narrowing in the space above your first rib. When this area closes, it can create a tighter space for nerves and blood vessels to travel through.

Thoracic outlet syndrome develops when the passageway becomes too narrow, and the blood vessels or nerves in your thoracic outlet are squeezed (compressed). This compression causes pain, numbness and other symptoms in your arm and hand.

The three types of thoracic outlet syndrome are:

• Neurogenic thoracic outlet syndrome: This type affects a group of nerves running from your spinal cord to your shoulder, arm and hand (brachial plexus). Neurogenic thoracic outlet syndrome (most common) makes up more than 90% of cases.
• Venous thoracic outlet syndrome: This type involves compression of a vein passing through your thoracic outlet, which can cause blood clots.
• Arterial thoracic outlet syndrome: This type occurs when bones of the thoracic outlet press on an artery, restricting blood flow. Increased pressure in the narrowed artery can cause a bulge in your artery wall (aneurysm).

You can develop more than one type of thoracic outlet syndrome if your bones compress more than one structure.

Symptoms vary between the types of thoracic outlet syndrome. Your symptoms may be constant or occur with certain movements or postures.

Common causes of thoracic outlet syndrome include: 

Risk factors are things that increase your chances of developing thoracic outlet syndrome. Possible risk factors include:

Diagnosis starts with a review of your symptoms and a physical exam. Your physician may try to trigger your symptoms by asking you to move your arms or head in specific ways.

Other tests your physician may order to diagnose thoracic outlet syndrome or rule out other conditions include:

• Medical imaging tests, such as X-ray, ultrasound, CT and MRI, to look at your bones, muscles, tendons and blood vessels.
• Electrodiagnostic tests, including electromyography and nerve conduction studies, to measure electrical activity in your nerves and muscles.
• Blood vessel studies, such as angiography (arteries) and venography (veins). Your physician inserts a thin, flexible tube (catheter) into your blood vessels to look for blood clots or aneurysms.

Treating thoracic outlet syndrome requires a specialized team approach. Your care team may include: 

• Heart and blood vessel (vascular) specialist 
• Musculoskeletal (orthopaedic) specialist 
• Physical therapist  
• Chest (thoracic) surgeon 
• Blood vessel surgeon

With a skilled team guiding your care, treatment is usually very effective.  

You can’t always prevent thoracic outlet syndrome, but reducing pressure on your thoracic outlet can help. Practice good posture and avoid carrying heavy bags over your shoulder.

It’s also important to keep the muscles in your neck, shoulders and chest strong and flexible. Ask your physician for stretching and strengthening exercises that you can do at home.