Thoracic Outlet Syndrome

We've got a messy diagnosis this week: thoracic outlet syndrome. David breaks the diagnosis down by anatomy and compressed structure to help make sense of a syndrome that has poor evidence and little consensus.

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Welcome back, everybody. Today we’re going to tackle a bit of a tricky diagnosis: thoracic outlet syndrome. If you’ve been studying the shoulder, neck, and thoracic region on your own, you might have noticed that this diagnosis is barely touched in Current Concepts. We currently have no high quality randomized controlled trials on thoracic outlet syndrome, and we definitely don’t have a clinical practice guideline. But this is still a diagnosis that you’re likely to see in the clinic, and we think it’s likely to show up on the exam. So I’m going to try to break it down simply and cut through some of the controversy to give you the general consensus of what has been published over the last five years.

Thoracic outlet syndrome—or TOS—is a syndrome, which means it’s a condition characterized by a group of symptoms, not necessarily by a diagnostic test or a clear understanding of etiology. That makes this a diagnosis of exclusion. It also means there is the potential that the symptoms could originate from different causes in different cases.

Let’s talk about the anatomy associated with TOS so we can build a framework to talk about diagnosis and potential causes. Thoracic outlet syndrome involves the compression of one or more neurovascular structures somewhere between the cervical spine and the axillary region. There are three main areas where this compression can occur: the interscalene triangle, the costoclavicular space, and the subcoracoid space deep to the pectoralis minor. As the brachial plexus passes through these three regions, it can be divided into three corresponding regions: the supraclavicular plexus (where the roots and trunks are located), the retroclavicular plexus (where the divisions are located), and the infraclavicular plexus (where the cords and branches are located).

Now let’s take a closer look at each area. The interscalene triangle is formed by the borders of the anterior scalene, the middle scalene, and the first thoracic rib. The C5-T1 roots and trunks pass through this area, along with the subclavian artery. Notably, the subclavian vein does not pass through the interscalene triangle—so if an individual has venous thoracic outlet syndrome, the inter scalene triangle is not the site of entrapment. A small percentage of the population might have a cervical rib or an elongated C7 transverse process with a fibrous band that connects to the first thoracic rib, and these structures could contribute to neurovascular compression. However, many individuals who have these anatomic anomalies have no thoracic outlet symptoms, so the presence of one of these structures should be considered an incidental finding unless everything else is pointing you toward TOS and the abnormality correlates with symptoms. It is also thought that scalene abnormalities, like hypertrophy, first rib abnormalities, like an elevated first rib, or postural abnormalities, like forward head posture could also contribute to neurovascular compression in this area.

Moving on to the second site of entrapment, the costoclavicular space is the space between the first thoracic rib and the clavicle. The costoclavicular ligament forms a medial border here, and the insertion of the anterior scalene forms a lateral border. The divisions of the brachial plexus pass through this region, as well as the subclavian artery and vein. This is the most common site of subclavian vein compression. Bony abnormalities in the first rib or clavicle, such as a callus from a fracture, could contribute to compression here, as could a depressed and retracted shoulder girdle. Repetitive trauma, such as from repeated throwing, can also become a problem here.

The third site of entrapment is the subcoracoid space. Here, the coracoid process forms the superior border, the pec minor forms the anterior border, and the chest wall forms the posterior border. The brachial plexus cords pass through this space, and the branches form just distal to it. The subclavian artery and vein also pass through here, but they are renamed the axillary artery and vein. Again, a depressed and retracted shoulder girdle could cause compression here, as could potential pectoralis minor tightness or hypertrophy. This area can be particularly problematic when the upper extremity is elevated above shoulder height, since the neurovascular bundle has to pass inferior to the coracoid and then turn superiorly. So tasks that involve an elevated arm position can increase neurovascular compression at this site.

So to recap: the interscalene triangle is where the brachial plexus roots and trunks or the subclavian artery can become compressed, most likely due to a bony abnormality like a cervical rib or elongated C7 transverse process or due to some hypertrophy or abnormal tension or posture affecting the scalenes. The costoclavicular space can compress the divisions of the brachial plexus as well as the subclavian artery and vein due to posture, bony abnormalities in the clavicle or rib, or repetitive trauma. And the subcoracoid space can compress the brachial plexus cords or the axillary artery or vein. This may be associated with pec minor tightness, posture, or overhead activities.

So now that we’ve broken TOS down by anatomy, let’s break it down by the type of structure that can be compressed. In general, thoracic outlet syndrome is broken down into three groups: neurogenic, arterial, and venous. We will cover the groups in that order. So first, neurogenic TOS.

Some prefer to break the neurogenic thoracic outlet syndrome category into two separate subcategories: “true neurogenic TOS,” which is where a structural anomaly like a cervical rib causes compression or tension to the C8 and T1 nerves; or “disputed neurogenic TOS,” where a structure compresses a portion of the upper brachial plexus. Clearly, some people don’t think “disputed TOS” is real. Instead of wading into that argument, we’re just going to talk about lower brachial plexus TOS (which some consider “true” TOS), and upper brachial plexus TOS (which some dispute). When you consider both of these together, neurogenic thoracic outlet syndrome is by far more common than arterial or venous TOS.

Lower brachial plexus TOS tends to affect those who are young to middle aged, and it’s more common in women. In this form of the syndrome, a structural abnormality like a cervical rib or a fibrous band or a hypertrophied scalene pulls the C8 and T1 nerves superiorly. Because T1 is more inferior, it gets tractioned more than C8, so patients can present with T1 and C8 symptoms that are usually worse in the T1 distribution. The thenar muscles are usually the most affected, and patients can present with thenar muscle atrophy that might make you think of carpal tunnel syndrome. Myotomally speaking, we’d also expect finger abduction and finger flexion weakness. Patients will usually have sensory symptoms as well—again, affecting T1 the most, but C8 can be affected too. So sensory symptoms can occur in the medial arm and forearm as well as the medial hand and 4th and 5th digits.

So let’s talk differential diagnosis: the thenar eminence atrophy can mimic carpal tunnel syndrome, but the sensory disturbances will be on the wrong side of the hand. Sensory symptoms into the 4th and 5th digit might make you think of an ulnar nerve entrapment, but remember that the ulnar nerve does not provide any sensory distribution to the arm or forearm. So if there are symptoms in the arm of forearm, it’s not ulnar nerve.

That leaves thoracic outlet syndrome and cervical radiculopathy as the most likely remaining diagnoses. Your cervical radiculopathy clinical prediction rule will help you here. Both conditions may include positive upper limb tension tests, so that test probably won’t help. Cervical rotation <60 degrees is more likely in cervical radiculopathy, but it’s also possible in thoracic outlet syndrome. However, TOS is unlikely to be associated with positive cervical distraction or Spurling’s tests—so a thoracic outlet syndrome case is going to fall short of the 3 out of 4 positives you need for a positive cervical radiculopathy cluster.

Finally, a pancoast tumor can sometimes affect the lower brachial plexus, so if a patient presents with a C8/T1 distribution of symptoms and a negative cervical radiculopathy cluster, be sure you’re also screening for any red flags or signs of lung cancer.

So that covers lower plexus thoracic outlet syndrome. Now let’s look at upper plexus thoracic outlet syndrome. Recall that this version of TOS is disputed, so the literature on it is not as consistent. Theoretically, an upper plexus entrapment should affect C5 and C6, but these patients often have pain beyond the C5 and C6 distribution. Generally, these patients might present with pain in the shoulder that radiates into the ipsilateral head and neck, the anterior and posterior aspects of the thorax, and the proximal aspect of the arm. Any motor impairments or sensory disturbances will present in a C5 or C6 distribution. So think sensory changes down the lateral arm from the shoulder region to the lateral two fingers and weakness in shoulder abduction, elbow flexion, and wrist extension. Symptoms may be activity or position dependent and be provoked by tasks requiring UE exertion or elevation. As we mentioned, this is going to be a diagnosis of exclusion. So don’t worry too much if there’s disagreement in the sources about how these symptoms might be described. If they have sensory and/or motor deficits that fit a C5 and C6 pattern and are aggravated by specific UE positions or are accompanied by a negative radiculopathy cluster, you can suspect upper plexus TOS.

Let’s move on to venous thoracic outlet syndrome. Recall that the subclavian vein does not pass through the interscalene triangle, so it can only be affected at the costoclavicular space or at the subcoracoid space. Venous thoracic outlet syndrome is typically provoked by specific upper extremity tasks—and particularly by repetitive tasks like throwing. Acutely, symptoms may include upper extremity swelling, cyanosis, presence of collateral veins in the upper extremity, and achy pain with exertion. Venous thoracic outlet syndrome is associated with venous thrombosis, so if a patient presents with acute venous thoracic outlet syndrome and thrombosis has not been ruled out, they need to be sent to urgent care to rule it out before proceeding. A thrombosis in the axillary or subclavian vein due to repeated trauma or exertion is sometimes called an “effort thrombosis” or “Paget-Schroetter syndrome.” The OCS really likes to throw obscure names of conditions and syndromes at you, so remember that Paget-Schroetter syndrome is the same as an effort thrombosis, which is a thrombosis in the axillary or subclavian vein related to a repetitive upper extremity task.

Finally, we’ll cover arterial thoracic outlet syndrome. Arterial TOS is the least common of the three types. Like the other two, it tends to affect adolescent to middle aged individuals. Since the subclavian artery passes through all three potential entrapment sites, it could be compressed due to anatomical abnormalities or provocative positions at any of the three sites. Patients may demonstrate pain with upper extremity effort, easy fatigability, claudication, extremity coolness, pallor, decreased capillary refill, an audible bruit, and decreased or absent distal pulse. And again, these symptoms may be worse or only occur in certain postures or upper extremity positions. If the condition has been left untreated and becomes chronic, stenosis or aneurism may occur, and patients might report associated shoulder and neck pain. Like venous TOS, arterial TOS can be associated with thrombosis, so watch out for signs of thrombosis in these patients.

The only condition I can think of that might mimic arterial TOS is peripheral arterial disease in the upper extremity. One way to differentiate the two is by considering age and cardiovascular risk factors: thoracic outlet syndrome tends to affect a younger demographic than peripheral arterial disease. One test that differentiates between the two is Allen’s test. In Allen’s test, the examiner compresses both the radial and ulnar arteries at the wrist, and the patient pumps his or her hand 10 times. This will encourage venous return of the blood in the hand, so the hand should appear pale and blanched. The examiner then releases one artery and times how long it takes for the hand to become flushed again. The test is performed once for each artery, and the test is positive if it takes longer than 6 seconds for the hand to become flushed again. This test is examining peripheral arterial flow, so as long as the patient is tested in a position that is not normally provocative for their symptoms, this test should be negative in thoracic outlet syndrome.

Before we conclude this section on diagnosis, I want to mention that even though it’s convenient to break TOS into neural, venous, and arterial categories, it is possible for patients to present with mixed findings if more than one structure is compressed.

Alright, now we’re going to wrap up this episode by considering examination and treatment together. Both in real life and on the exam, your treatment for thoracic outlet syndrome is going to be driven by your findings with the individual patient. Because different neurovascular structures could be compressed by different musculoskeletal structures in different places, you will want to do a thorough exam of posture, muscle tension, muscle length, and any bony abnormalities. If your findings correlate to the patient symptoms, great! Treat those findings. For example, if a patient presents with lower brachial plexus symptoms, cervical screen is negative, they have a positive cervical rotation lateral flexion test for first rib hypomobility, and they appear to have an elevated first rib, then great—that all seems to go together. Treat the first rib. If they have upper brachial plexus symptoms, are an apical breather, and have tight scalenes—that all seems to fit, so treat the scalenes and teach diaphragmatic breathing.

Beyond your standard assessments, special tests might help some. Thoracic outlet syndrome special tests very frequently have false positives for vascular symptoms, so positive findings are most helpful when they are positive for neurological symptoms or when they correlate well with the patient’s chief complaint. The most common tests are supposed to implicate specific structures, so it might be beneficial to know a couple of the most common tests and what treatment they might indicate.

Adson’s test involves palpating the radial pulse with the patient’s arm at their side while the patient ipsilaterally rotates and extends the neck. The patient then takes a deep breath and holds it. The goal here is to increase scalene tension, so a positive test might implicate scalenes.

The costoclavicular test and Halstead maneuver both involve shoulder girdle depression with the arm at the patient’s side, so both might implicate the costoclavicular space.

The passive shoulder shrug test is kind of the opposite of the costoclavicular test. It involves passively elevating the shoulder girdles. So if the compression is occurring at the costoclavicular space, this will be relieving.

Finally, Wright’s test, the hyperabduction test, and Roos test—which is sometimes called the elevated arm stress test, or EAST test—all place the arms in an overhead position. This makes the neuromuscular bundle pass under the coracoid and then deflect back superiorly, so pectoralis minor tightness and the subcoracoid space are most implicated in these tests.

Alright, let’s put all of this together in a case.

A 48-year-old male patient presents to your clinic with chief complaint of intermittent pain and fatigue in his hands. He is an avid hiker, and he notices it gets worse when he’s backpacking. As he hikes, he finds it is difficult to continue to hold his trekking poles. He notices his hands get cold and clammy, and he eventually has to stop hiking, set his gear down, and rest. Physical exam reveals normal cervical range of motion and negative Spurling’s tests bilaterally. Hoffman’s test is negative. He denies any gait disturbances.

First question: does this sound like neurogenic, arterial, or venous thoracic outlet syndrome? His symptoms here all point to ischemia: the fatigue and cold, clammy hands points to arterial thoracic outlet syndrome. If he had mentioned swelling and blue fingers, we would suspect possible venous TOS. And if he had paresthesias, we’d suspect neurogenic.

Next question: what other condition do you need to rule out, and what physical exams would help? In this case, the other condition his symptoms most closely mimic is peripheral arterial disease. Allen’s test could be useful for checking peripheral circulation. Diminished distal pulses in non-provoking positions could also point to PAD.

Third question: what special test would be most useful in confirming your suspected diagnosis? Is it A. Adson’s, B. costoclavicular test, C. Wright’s test, or D. Roos test? In this case, I’m going to say costoclavicular test. Wright’s and Roos both test the arm in an elevated position, and this patient does not have symptoms in that position. Adson’s test is intended to implicate the inter scalene triangle, but his cervical ROM is clear. His complaint and aggravating behaviors suggests to me that the compression may be occurring at the costoclavicular space, and so I think the costoclavicular test is the best choice here.

Finally, what treatment is going to be most appropriate? A. Pec minor stretching, B. Seated postural reeducation, C. Scalene soft tissue mobilization, or D. Proper backpack fitting? Each of these treatments might be appropriate for some thoracic outlet syndrome patients. In this case, since the patient is experiencing his symptoms specifically when backpacking, and since it sounds like compression is occurring at the costoclavicular space, properly fitting the patient’s backpack is most likely to relieve his symptoms. Working on hiking posture and improving shoulder girdle strength to better carry the backpack and reduce compression would be other reasonable options as well. The key is to read the case carefully and correlate your treatment to the findings and to the chief complaint.

Well that wraps up this episode. I hope this helped give you a framework for understanding thoracic outlet syndrome just a little bit better. I think it’s likely to show up in some form on the exam, and if I was the one writing the questions, this is what they’d look like.