Thoracic outlet syndrome (TOS) is a term used for a group of disorders caused by the compression of nerves, veins, or arteries as they pass through a tight passageway between the collarbone and topmost rib to the arms. The compression of these structures results in a range of symptoms, including neck, shoulder, arm, and hand pain; numbness and tingling sensations; and arm and hand weakness, among others.

TOS is a rare disorder. It’s estimated that there are between 3 and 80 cases of TOS for every 1,000 people. The condition is more common in women than in men, and while it can affect people of any age, it most commonly occurs in people between ages 20 and 50.

Fortunately, effective treatments are available for thoracic outlet syndrome, and most people with the condition have a good prognosis.

Thoracic outlet syndrome is an umbrella term for disorders in which nerves, veins, or arteries in the thoracic outlet—the space between the collarbone and first rib (at the top of the rib cage)—are compressed. The compression of these nerves, veins, or arteries impairs their ability to work properly and gives rise to a range of symptoms, including shoulder, neck, and/or arm pain, as well as numbness or a “pins-and-needles” feeling in the hand.

A number of nerves, blood vessels, and muscles pass through the thoracic outlet, including:

• Brachial plexus: a network of nerves that connects to the spinal cord in the neck and upper back and controls movement and sensation in the shoulder, arms, forearms, and hands.
• Subclavian artery: a large artery that delivers oxygen-rich blood to the arm. It is located below the collarbone (“subclavian” means below the clavicle, also known as the collarbone).
• Subclavian vein: a deep vein that passes below the clavicle and drains blood from the arm.

In people with thoracic outlet syndrome, one or more of these structures are compressed as they pass through the congested space of the thoracic outlet.

There are three types of TOS, based on which one of these three structures is compressed:

• Neurogenic thoracic outlet syndrome occurs when a brachial plexus nerve is compressed, leading to problems with sensation and/or movement of the shoulder, arm, hand, or fingers. Neurogenic TOS accounts for over 90% of cases.
• Venous thoracic outlet syndrome occurs when the subclavian vein is compressed. When this happens, blood doesn’t drain from the arm as efficiently as it should, leading to symptoms, including arm swelling and pain. Blood clots can also form in the vein, further reducing blood flow. The blood clots can also break away and travel to the lungs, where they can cause a pulmonary embolism. Venous TOS accounts for 3–5% of cases.
• Arterial thoracic outlet syndrome occurs when the subclavian artery is compressed. This reduces the amount of blood that reaches the arm, resulting in arm and hand pain and numbness. Over time, compression can damage the inner layer of the artery and increase the risk of an aneurysm (abnormal bulging of the artery) and blood clot formation. Blood clots can get lodged in blood vessels, reducing or blocking blood flow, resulting in tissue damage. Arterial TOS is the least common type of TOS, accounting for around 1–2% of cases.

Thoracic outlet syndrome can affect one or both sides of the body, and in some cases, people may have more than one type of TOS at the same time.

TOS can be caused by the following:

• Anatomical abnormalities, which can press against blood vessels and/or nerves in the thoracic outlet. For example, TOS is sometimes caused by an extra rib, known as a cervical rib, above the top of the rib cage. In other cases, the first rib—the uppermost rib in the rib cage—extends into the thoracic outlet, causing TOS. A broken collarbone that doesn’t align properly after healing can also press against blood vessels or nerves, as can muscles or ligaments that pass through the thoracic outlet.
• Injury, for instance, from a car accident or fall, can damage bones and other structures in and around the thoracic outlet, resulting in the compression of blood vessels and/or nerves. Repetitive overhead arm movements can also cause swelling or growth in muscle size, leading to the compression of structures in the thoracic outlet. (Those repetitive movements are often sport- or workplace-related and include activities such as swimming, sports involving overhead throwing, and lifting weights above the head.)
• A tumor in or around the thoracic outlet can physically press against other structures in the thoracic outlet.
• Swollen lymph nodes, for instance, from Hodgkin lymphoma, may press against nerves or blood vessels in the thoracic outlet.

Symptoms of neurogenic TOS, in which nerves are compressed, can include:

• Neck, shoulder, chest, and/or arm pain
• Pain along the inside of the forearm
• Headache
• “Pins-and-needles” feeling, tingling, or numbness in hand and fingers
• Arm, hand, and finger weakness
• Clumsy hand control
• Hand coldness
• Finger swelling
• Changes in hand color

Symptoms of venous TOS, in which veins under the collarbone are compressed, may include:

• Arm swelling, pain, and/or heaviness
• Bluish skin on the arm and hand

Symptoms of arterial TOS, in which an artery under the collarbone is compressed, may include:

• Arm and hand pain
• Numbness in hand and/or fingers
• Arm and hand coolness and paleness
  

To diagnose TOS, your doctor will review your medical history, perform a physical exam, and run one or more diagnostic tests.

Talk to your doctor about your symptoms, when they began, and whether they typically occur or worsen during or after certain activities. During a physical exam, your doctor will check your blood pressure, assess your posture, and closely examine your shoulder, neck, chest, ribs, arms, and hands for signs of TOS. They may ask you to perform certain movements with your arms and neck to try to reproduce your symptoms. For instance, you may be asked to raise your arms over your head with your elbows bent at 90 degrees. You’ll then open and close your hands for three minutes while holding this position. If you have symptoms during this test, it may indicate that you have TOS.

Additional tests are necessary to confirm the diagnosis. These may include:

• Imaging tests such as a chest and spine X-ray, magnetic resonance imaging (MRI) scan, magnetic resonance angiography (MRA), computed tomography (CT) scan, or ultrasound. These tests produce images of internal structures in the neck, shoulder, and chest.
• Electromyography (EMG) measures the electrical activity of a muscle. In this test, a small needle is inserted into a muscle. The needle records electrical activity in the muscle while it is at rest and while you contract it. EMG helps doctors determine whether the muscle weakness is caused by a nerve problem.
• Nerve conduction studies measure the speed at which nerves conduct electrical impulses. This test delivers an electrical current to nerves through electrodes attached to the skin or small needles inserted directly into nerves. The current travels along the nerve until it reaches a muscle, causing it to contract.
• Anterior scalene and pectoralis minor muscle block, a test in which a local anesthetic is injected into the anterior scalene muscle (a muscle in the neck that connects to your spinal nerves) and/or the pectoralis minor (a muscle in your upper chest). If the injection relieves symptoms, it lets doctors know that the injected muscle is the site of the compression of nerves or blood vessels.

Several treatment options are available for TOS, including:

Physical therapy. Exercises and stretches targeting the muscles around the shoulder can strengthen them, as well as improve posture, muscle balance, and range of motion. Physical therapy can also help relieve symptoms by reducing the compression of blood vessels or nerves.

Lifestyle changes. Activity modifications may help reduce symptoms and make symptoms occur less frequently. They include:

• Avoiding activities that cause symptoms to occur
• Rearranging work areas so they can be used comfortably and with good posture
• Learning and practicing relaxation techniques
• Losing weight (for those who are overweight)

Medications. Several types of medications may help relieve symptoms, including:

• Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, aspirin, and naproxen.
• Muscle relaxants
• Antidepressants
• Anticonvulsants
• Selective serotonin reuptake inhibitors (SSRIs)

Muscle injections of a local anesthetic, steroids, or Botox (botulinum toxin) may also alleviate symptoms.

People with venous or arterial TOS may need blood thinners to prevent blood clots from forming. In some cases, however, blood clots may be cleared from a blood vessel via a procedure called catheter-directed thrombolysis. In this procedure, a catheter is moved through the blood vessel so that clot-dissolving medication can be directed at the clot.

Surgery. If TOS is caused by an extra rib or other structural problem, surgery may be necessary. Surgery also treats those whose symptoms have not improved with physical therapy and other nonsurgical treatments.

Various surgical procedures are used to treat TOS. The choice of procedure depends on the type of TOS and the underlying cause of the condition. In most cases, surgery involves an incision made either above or below the collarbone or in the armpit.

Surgery may be performed to remove structures compressing nerves or blood vessels in the thoracic outlet. This is referred to as “decompression” surgery and includes:

• Full or partial removal of the first rib (the rib just under the collarbone)
• Removal of a cervical rib (an extra rib above the first rib)
• Removal of the scalene muscles (three muscles that run along both sides of the neck, two of which may be involved in TOS)
• Making an incision in the tendons of the pectoralis minor muscle

Surgery may also be necessary if any blood vessels have developed problems such as narrowing, aneurysm (abnormal bulging), or blood clots. Surgery for these and other blood vessel problems may involve (among other procedures) removal of part of a blood vessel, grafting a blood vessel taken from elsewhere in the body or from a donor onto the affected vein or artery to reroute blood around the problem area, or implantation of a stent (a small mesh tube) in a vein or artery that has become narrowed.

In general, the outlook for people with TOS is excellent. For the vast majority of people—about 90% of cases—the condition can be successfully treated with physical therapy and lifestyle changes. Outcomes after surgery are also good. However, some people may experience recurring symptoms after physical therapy and surgical treatment. In these cases, additional treatment, including an additional surgical procedure, may help alleviate symptoms.

This article was medically reviewed by David Strosberg, MD, MS.