Thoracic outlet syndrome is a poorly understood group of diseases that, in its most common form, is difficult to diagnose, frustrating to treat, and often not well understood by both patients and physicians.  In this section, we will discuss the conditions that are lumped together under the heading of thoracic outlet syndrome, even though they have widely differing signs and symptoms.

WHAT IS THE THORACIC OUTLET?
Arteries and veins pass from the chest (thoracic cavity) to the shoulder and arm. These vessels leave the chest by passing through the thoracic outlet.   The thoracic outlet can be understood as a triangle comprised of the collarbone (clavicle), the underlying first rib, and two small parallel muscles each roughly the size of a finger. One can locate this area on one’s own body by feeling just behind the part of the collarbone closest to the base of the neck.  The area is an outlet in the sense that the nerves and the main artery and vein to the arm pass through this rather tight, small triangle on their way out of the neck and chest.  The pathologic conditions grouped under the diagnosis of thoracic outlet syndrome usually involve compression of either the nerves, vein, or artery as they pass through the triangle of the thoracic outlet. 

NERVE COMPRESSION IN THE THORACIC OUTLET
The most common form of thoracic outlet syndrome involves compression of one or more of the large nerves that pass from the neck to the arm and shoulder.  This group of nerves is called the brachial plexus.  Persons with compression of the nerves in the thoracic outlet often complain of pain in the neck, shoulder and/or arm in varying locations.  This pain is often described as severe and tends to run down the arm and is aggravated by moving the arm.  Movement of the arm above the horizontal plane and above one’s head is often excruciating; most patients with this condition will not willingly lift their affected arm unless ordered to do so during examination.  Patients often complain of headaches that affect only the side of the head that is closest to the painful arm (hemicranial headache).  Pain medication is usually only of limited effectiveness in these cases.

Patients with thoracic outlet syndrome caused by nerve compression (neurogenic thoracic outlet syndrome) may be born with abnormalities of the two small muscles (the anterior and medial scalene muscles) that form one side of the thoracic outlet.  In addition, these patients may have an extra rib (cervical rib) that compresses structures in the thoracic outlet.  Patients born with these conditions do not usually experience symptoms until adulthood.

The patient with no congenital abnormalities may acquire neurogenic thoracic outlet syndrome.  This is usually caused by an injury.  Rarely, fracture of the first rib or collarbone may lead to thoracic outlet syndrome.  However, the large majority of patients with acquired neurogenic thoracic outlet syndrome have an injury to the scalene muscles leading to nerve compression.  Whiplash-type car injuries are a classic cause of this problem, but many other types of injury to the arm, shoulder, and neck can result in thoracic outlet syndrome.  More recently, there has been an association of thoracic outlet syndrome to repetitive tasks often seen in persons working with a keyboard. Thus, thoracic outlet syndrome, like carpal tunnel syndrome, can be one of the “repetitive motion injuries” seen with increasing frequency these days.

DIAGNOSIS OF NEUROGENIC THORACIC OUTLET SYNDROME
There are two principal difficulties in diagnosing this condition. Firstly, few physicians know much about this condition, so patients have typically gone to several physicians before being referred to the proper office.  It is not unusual for the patient to be labeled as a malingerer, or to have been told that the pain is in their head, or for the physician to tell the patient that there is nothing wrong.  Needless to say, patients become frustrated with this treatment.

The second main problem in the diagnosis of this condition is that there are usually no tests that accurately diagnose neurogenic thoracic outlet syndrome.  X-rays of the neck may reveal a cervical rib, but in most cases no abnormalities are seen.  CAT scans or MRIs are equally nondiagnostic.  Nerve conduction studies are often performed and are only useful to show that the nerves are damaged.  A patient with intermittent pain from compression of the nerves will generally have a normal nerve conduction test.

The diagnosis is made by taking a careful history and performing a careful physical examination on the patient, followed by excluding other possible diagnoses.  Tenderness of the thoracic outlet near the base of the neck just behind the collarbone is one of the two most telling signs of this condition.  Reproduction of the pain by having the patient hold their hands is a position of surrender above the level of the shoulder and repeated forceful clenching and unclenching of the hands, often for several minutes, is the other characteristic sign of neurogenic thoracic outlet syndrome.  Patients should have a CAT scan or MRI of the neck to prove that there is no pinched nerve in the neck which can cause a similar pain syndrome.  Nerve conduction studies may be useful in patients with a history of injury to prove that the pain is not from actual damage to the nerves.  Carpal tunnel or ulnar nerve compression at the elbow may also be diagnosed by this test.  Orthopedic consultation is useful to exclude problems with the shoulder joint as the source of the pain.  In general, the diagnosis is made by proving the other possibilities do not exist (diagnosis of exclusion).  This is a tedious and time-consuming procedure.  This is a diagnosis made the old-fashioned way, not with technology and scans.

TREATMENT OF NEUROGENIC THORACIC OUTLET SYNDROME
A trial of physical therapy is almost always indicated as the first line of treatment. Strengthing and range-of-motion exercises coupled with heat or ultrasound may afford significant relief.  However, some patients’ symptoms are made quickly worse by physical therapy; in these cases therapy should be immediately discontinued.

If the patient has persistent pain, the decision should be made by the patient and the physician whether or not to proceed to surgery.. If the symptoms are tolerated by the patient, then no surgery is recommended. However, if the symptoms are not tolerable or prevent employment, serious consideration should be made to perform surgery.

Surgery unfortunately is only successful in about two out of three cases; patients are often better, but rarely completely symptom-free.  Removal of the scalene muscles and sometimes the first rib opens up the thoracic outlet and allows for more space for the nerves to pass through.  Complications of surgery include injury to the lung, nerves, vein, or artery.  As with most shoulder surgeries, postoperative physical therapy is often mandatory to regain good mobility, even in the best of cases.  Patients who do not obtain relief often have irreversible nerve damage or there may be a different, undetected cause for the pain.  Hospitalization ranges from two to six days.  Symptoms can sometimes recur in the same arm due to scarring around the nerves.  This can sometimes be treated by reoperation.

VEIN COMPRESION AND THROMBOSIS IN THE THORACIC OUTLET
The second most common form of thoracic outlet syndrome involves compression and injury to the main (subclavian) vein as it passes through the thoracic outlet.  This usually involves pinching of the vein by the first rib and scalene against the backside of the collarbone.  If the vein is sufficiently injured, it will clot, obstructing the flow of venous blood from the arm.  This is also called effort thrombosis or Paget-Schroetter syndrome.

This has been termed effort thrombosis because patients with this condition have often repeatedly performed activities that have involved straining of the neck muscles.  Weight lifters and baseball pitchers are classical examples of individuals who may have this condition.  However, thrombosis may be caused by smaller degrees of exertion.  Patients may sometimes have a condition of their blood that abnormally predisposes to clotting (hypercoagulable state).  Rarely, trauma to the area of the thoracic outlet may lead to subclavian vein thrombosis.

Patients present with an arm swollen up to the armpit, pain, difficulty moving the arm, bluish discoloration of the arm, and engorgement of the veins of the arm.  Diagnosis is made by physical examination followed by ultrasound or x-rays of the vein (venography).

In patients with this condition but few signs or symptoms, or who are not very active, treatment may consist of the administration of a blood thinner (heparin) to prevent further clotting.  However, in active individuals, treatment with heparin only may lead frequently to long-term disability and chronic problems with using the arm.  In younger, active, symptomatic patients, the clot is dissolved with the use of special clot-dissolving drugs delivered into the clot with a small catheter inserted in an arm vein up to the region of the thoracic outlet.  After a matter of several hours to a few days, the clot is dissolved.  Surgery is then performed to remove the scalene muscles and/or first rib that are compressing the vein.  After surgery, the vein is examined by x-ray again to determine if there is and persistent narrowing of the vein caused by the clot and the chronic compression.  At this time, any narrowing may be opened with a balloon catheter inserted into the vein.  Postoperatively, patients are given oral blood thinners (Coumadin) for several months.

ARTERY COMPRESSION IN THE THORACIC OUTLET
Significant compression of the main (subclavian) artery in the thoracic outlet is extremely rare.  This is usually caused by congenital abnormalities of the thoracic outlet.  Patients may present with a cold, pulseless, painful arm if the compression has caused complete blockage of the artery.  More often, the patient will complain of the sudden appearance of a cold, painful, blue finger or fingers.  This represents small clots passing from the artery where it is compressed in the thoracic outlet down to the small arteries in the hand or fingers.  Often there is a bulging of the artery (aneurysm) near the point of compression.  Diagnosis is facilitated by the use of ultrasound and x-rays with contrast (angiogram, arteriography).  Treatment involves removal of the compression in the thoracic outlet by removing the scalene muscles and/or the first rib, repair of the subclavian artery, administration of blood thinners (heparin) and a procedure called a sympathectomy, which improves blood flow to the fingers.