DIAGNOSIS OF TOS

How is a TOS diagnosis made?

The diagnosis of thoracic outlet syndrome is challenging since in the vast majority of cases there is no universal test reliably demonstrating the presence of the disease. Big part of the diagnosis comes from awareness of TOS as a potential cause of patient symptoms. Even experienced physicians may fail to recognize signs and symptoms of TOS. One study from USA demostrated that on average patients visited 4 different doctors before the correnct diagnosis was made [1]. However, once the thoracic outlet syndrome is suspected there is high chance that the diagnosis is correct. A study from large refferal center in the USA demostrated that the percentage of the correct diagnosis from doctors' referal was 91% and from patients self-referral was 97% [2]. This study shows that patients are almost (or maybe even better) as good as doctors in suspecting TOS.

Although suspecting TOS is very important significant work needs to be done to confirm the diagnosis. There is no single reliable test used to detect TOS. Therefore, the diagnosis is made by combination of clinical and radiological findings. Making diagnosis of TOS is like putting pieces of a puzzle. A highly experienced doctor is required to perform clinical examination, interpret imaging and make differential diagnosis with other, similar diseases. Dr. Aghayev has been working with TOS patients for most of his career and is considered as internationally recognized expert in this area.

Clinical examination

Careful history and physical examination are essential keys to suspect the thoracic outlet syndrome. TOS is a chronic disease and patents report long-lasting symptoms. Particular attentions should be given to TOS specific symptoms like exercise induced pain or inability to perform overhead tasks. These "red flags" can point to the presence of TOS from the very beginnig of evaluation. After countless conversations with TOS patients I noticed that there is certain "TOS pattern". Recognizing this pattern is both conscious and intuitive.

Physical examination

Poor posture carries a risk for TOS development and I always check postural abnormalities. Kyphois, scoliosis, shoulder and collar bone asymmetry are frequently encountered in TOS patients. They are usually subtle and barely visible to untrained eye and therefore frequently missed. Pain and tenderness at the junction of the neck and shoulder area is very typical but not specific to TOS. Tapping of the thoracic outlet area from behind usually illicits pain and is my preferable test since it highly sensitive to TOS and is not seen in other diseases.

Neurological examination

Neurological examination should focus on muscle weakness and sensory deficits in the arm and hand. The correct examination requires deep knowledge of anatomy of brachial plexus, its branches and their skin/muscle distributions. Unfortunately, most physicians do not have such knowledge and experience and even most obvious deficits are frequently missed. Even if neurological examination is performed the findings are eiter missed or misinterpreted.

Motor (muscle strength) examination

The presence of atrophy (muscle wasting) is particularly important since it is an indicator of disease severity. Atrophy is usually prominent on thenar side of the hand. I check the atrophy by comparing two hands side by side. This way the presence of even subtle muscle wasting can be noted. All hand muscles are innervated by the lower pherart of brachial plexus – specifically by C8 and T1 nerve roots. These nerve roots are not usually affected by other diseases and therefore presence of C8 and T1 radicular symptoms is strong indication of TOS. Usually all hand muscles weak on testing. This clinical finding can be used to distinguish from other peripheral nerve entrapment neuropathies such as carpal tunnel syndrome and cubital tunnel syndrome. In carpal tunnel syndrome the median nerve is entraped in the wrist area under transverse carpal ligament. Clinically, some (but not all) thenar muscles are affected. These muscles are commonly recognized as LOAF muscles – L: lateral two lumbricals, O: opponens pollicis, A: abductor pollicis brevis, F: flexor pollicis brevis. In cubital canal syndrome all other hand muscles are affected. Significant number of TOS patients get wrong diagnosis of carpal or cubital tunnel syndrome and even undergo surgery. Wrong diagnosis and failed surgery may be avoided by knowing muscle groups affected by these syndromes and distinguishing them from thoracic outlet syndrome.

Sensory (skin feeling) examination

Neurogenic TOS causes variety of sensory disturbances. They include pain, paresthesia (pins and needlles), numbness in the affected area. Only numbness can be examined by clinician. Thorough sensory examination of entire arm and hand for all sensory modalities (touch, pain, temperature, vibration) is time consuming and usually not performed by doctors. Rather limited areas are superficially examined. Also there is significant confusion among doctors about sensory disturbances in TOS. Another problem arises from complexity of sensory innervation. Below is a picture of skin areas innervated by various nerves.

It is well known that the lower part of brachial plexus which comprises C8, T1 roots and inferior truncus (which forms by merge of C8 and T1 roots) is most frequently affected by TOS. This part of the brachial plexus innervates the inner (ulnar) side of the arm, forearm and hand. Therefore, presence of hypoesthesia in aforementioned area is quite typical for TOS. Yet, most clinicians fail to recognize hypoesthetic area as symptom of TOS. In fact, usually the hypoesthesia on the ulnar side is considered as sign of ulnar nerve entrapment in the cubital canal. However, ulnar nerve doesn't provide sensory innervation to arm and forearm. Only inner (ulnar) side of the hand including last two fingers are innervated by the ulnar nerve. In other words sensory area affected by TOS is much larger than ulnar nerve's skin area. The medial side of the arm and forearm are innervated by other nerves - intercostobrachialis and medial cutaneous antebrachial nerves. Neurogenic TOS affects mostly C8/T1/inferior trunk and all its braches - ulnar, medial cutaneus antebrachial, intercostobrachial. Medial cutaneous antebrachial nerve has highest diagnostic value and its involvement is almost encountered exclusively in TOS. Alas, doctors almost never pay attention to this nerve.

Typical skin areas affected in TOS vs cubital canal syndrome

Provocative maneuvers

Provocative testing is an essential part of clinical examination. The purpose of these tests is to elicit TOS symptoms using specific clinical maneuvers in order to establish diagnosis.

Elevated arm stress tests (EAST or Roos test). It is most commonly used and most informative test for diagnosing TOS.
Upper limb tension tests (ULTTs). These are several tests aimed to evaluate various nerves of the arm. One of them is performed with arms abducted, palms dorsiflexed and head is tilted. If pain is experienced the test is considered positive.
Adson test is frequently used to diagnose arterial compression. This test lacks specificity for TOS though.
Eden's test or military brace test
Wright's test
Cyriax release

Radiological examination

Radiographic examination plays an important role in diagnosing TOS. X-ray, CT scan, MRI, and Doppler USG are commonly used radiological tools.

X-ray is a very good tool to visualize bone structures. If accessory cervical rib is present, it will be visible on plain X-ray. However, even very experienced doctors may not be able to correctly read images. Also cervical accessory rib may be in the form of elongated C7 transverse process which will make diagnosis even more difficult. Other bone abnormalities are rib or clavicle fracture, pseudoarthrosis or excessive bone callus formation due to old fracture, and thinkening of the first rib. X-ray is also helpful to differentiate advanced cervical degenerative disc disease from TOS. Disc space narrowing with bone spurs formations may indicate that disc degeneration and compression at foraminal level may be real reason behind patient symptoms. Very often patients with neurogenic TOS have loss of lordosis (neck straightening) or even cervical kyphosis. Physicians may incorrectly interpret this finding as a symptom of cervical degeneration. In fact loss of lordosis is very common in TOS and is body's natural reaction to pain.
CT scan is also an excellent tool to visualize bone as well as soft tissue. CT angiography (CTA) is a superb tool to demonstrate subclavian vessels in a non-invasive way. Three-dimensional CT and/or CTA reconstructions can be particularly helpful for preoperative assessment.
Doppler ultrasonography or Duplex scan is a non-invasive method to evaluate blood flow in the vessels. It is particularly useful in vascular TOS cases. It can demonstrate the presence of subclavian vein thrombosis. High-resolution USG of the brachial plexus is a relatively new method to visualize the brachial plexus and can directly demonstrate the site of compression.
MRI is the most effective tool to demonstrate soft tissue. It can differentiate TOS from cervical disc disease. MRI neurography visualizes the brachial plexus itself with high accuracy. Diffusion tensor imaging (DTI) can demonstrate nerve fiber orientation in the brachial plexus and show potential compression sites.

3D CT angiographic reconstruction from a patient with TOS. Note that the subclavian artery narrows as it passes over the accessory rib. The accessory rib makes an abnormal joint with the first rib (white circle).

Nerve conduction studies

Nerve conduction studies like EMG and ENG may be helpful, but in the majority of cases, they do not provide a definitive diagnosis. Thus, the diagnosis is mainly made by careful clinical examination.

References

1. Landry GJ, Moneta GL, Taylor LM, Jr., Edwards JM, Porter JM. Long-term functional outcome of neurogenic thoracic outlet syndrome in surgically and conservatively treated patients. J Vasc Surg. 2001;33(2):312-317; discussion 317-319. https://doi.org/10.1067/mva.2001.112950

2. Likes K, Rochlin DH, Salditch Q, et al. Diagnostic accuracy of physician and self-referred patients for thoracic outlet syndrome is excellent. Ann Vasc Surg. 2014;28(5):1100-1105. https://doi.org/10.1016/j.avsg.2013.12.011

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DIAGNOSIS OF TOS

How is a TOS diagnosis made?

Clinical examination

Physical examination

Neurological examination

Motor (muscle strength) examination

Sensory (skin feeling) examination

Provocative maneuvers

Radiological examination

Nerve conduction studies

References

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Contact Form

DIAGNOSIS OF TOS

How is a TOS diagnosis made?

Clinical examination

Physical examination

Neurological examination

Motor (muscle strength) examination

Sensory (skin feeling) examination

Provocative maneuvers

Radiological examination

Nerve conduction studies

References

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