Abstract
Thoracic outlet syndrome (TOS) is a relatively uncommon condition that involves compression of portions of the brachial plexus (neurogenic or nTOS), arteries (aTOS), or veins (vTOS). The signs and symptoms of this condition can include pain in the neck, shoulder, and arm with paresthesias and pallor in the hand and may mimic other more common problems such as cervical radiculopathy and Raynaud phenomenon. A thorough history, physical examination, and interpretation of appropriate imaging modalities are essential to properly diagnose and treat TOS. The presence of a cervical rib in the setting of arm symptoms can raise suspicion. Treatment options include physical therapy, postural exercises, botulinum toxin injections, and surgical decompression with possible cervical rib resection in the appropriate setting.
Keywords
Adson maneuver, Arterial thoracic outlet syndrome, Cervical rib, EAST maneuver, Neurogenic thoracic outlet syndrome, Thoracic outlet syndrome, ULTT maneuver, Venous thoracic outlet syndrome
Introduction
Thoracic outlet syndrome (TOS) has all the components of a challenging disease entity. It is a syndrome that can disable young people, yet there is no gold standard for diagnosis or management. Some consider it overdiagnosed, whereas others consider it underdiagnosed. As a result, there is a wide range in prevalence estimates that vary from 0.03% to 8% of the population. The majority of these patients are women aged 30–50 years. Without a gold standard test, the practitioner must rely heavily on history for diagnosis. Knowledge of the subtypes of TOS and the anatomy surrounding the brachial plexus ( Fig. 22.1 ) are valuable tools in better understanding this disease.
TOS is an intentionally broad term. It was named by Peet in 1956 to unite a group of disorders that resulted from compression of the brachial plexus at different sites ( Fig. 22.2 ). Later Wilbourn subdivided TOS, not as before by anatomic compression site, but by the nerve or vessel compressed. He named the subtypes: arterial TOS (aTOS), venous TOS (vTOS), true neurologic TOS, and disputed neurologic TOS. When it comes to management, however, both the vessel and the site of compression must be considered.
The “thoracic outlet” is a neurovascular canal that tunnels over and under muscular and bony structures from the neck to the axilla ( Fig. 22.3 ). The most common sites of compression or entrapment are the interscalene triangle, the costoclavicular space, and the subpectoral triangle. The interscalene triangle is formed by the anterior scalene (anterior), middle scalene (posterior), and medial first rib (inferior). The costoclavicular space is formed by the clavicle (anterior) and first rib (posterior). The subpectoral triangle is formed by the coracoid process (superior), pectoralis minor (anterior), and ribs 2–4 (posterior). Anatomic anomalies, such as fibrous bands and the pre- or postfixed brachial plexus, are being increasingly recognized as potential predisposing factors. Similarly, cervical ribs may predispose a patient to TOS.
Pathology at these sites can cause either vascular or neurologic TOS, and each subtype presents differently. About 95% of all cases are neurologic TOS, and up to 99% of these cases are the disputed neurologic subtype. In the 1% of neurologic cases that are called “true,” there is a bony abnormality such as a cervical rib found or abnormalities on electrodiagnostic studies. The most common mechanism of injury resulting in TOS is neck hyperextension injuries followed by work-related repetitive strain.
Solid malignancies, especially Pancoast tumors in the lung apex, can present similarly. It is also important to consider circulatory conditions such as vasculitis, acute coronary syndrome, and vasospastic disorders. Complex regional pain syndrome and fibromyalgia must also be considered.
Neurogenic Thoracic Outlet Syndrome
History
Neurogenic TOS (nTOS) is the most common and reported as about 90% of all TOS cases. As previously mentioned, patients may present with symptoms similar to other commonly seen musculoskeletal disorders. The symptoms may be intermittent and positional or involve the upper (upper TOS) or lower trunk. Because the lower trunk of the brachial plexus is typically involved, complaints often involve numbness and tingling in the fourth and fifth digits of the affected side or sides. Reports of “upper TOS” describe compression of the superior plexus in the scalenes. When the upper trunk is affected, patients report neck, shoulder, and facial pain with paresthesias that follow the fifth and sixth cervical nerve roots and upper trunk. Pain and numbness may be exacerbated with overhead activity and having the arm outstretched. The symptoms of nTOS often include the feeling of arm heaviness and fatigability and also depend on the portion of the brachial plexus compressed. Symptoms are exacerbated by overhead activity or prolonged activity without arm support. Color changes to the hand are often seen with nTOS from sympathetic fiber activation after nerve compression. In severe cases, muscle weakness and atrophy occurs in the affected nerves’ distribution.
The symptoms of nTOS may mimic cervical radiculopathy with neck pain and radiating pain and paresthesias into the shoulder and arm. Numbness in the hand with radiation up the forearm is commonly seen in carpal tunnel syndrome. Ulnar neuropathy at or above the elbow can have a similar distribution of numbness and symptoms in the arm. The so-called double crush syndrome with compression of a cervical nerve root and in the carpal tunnel or cubital tunnel can be mistaken for nTOS.
Physical Examination
Patients may present with altered sensation and/or weakness and wasting of musculature in the affected limb in the distribution of the affected portion of the plexus. There is no gold standard physical examination maneuver for neurogenic TOS. Also, the rate of false positives using these maneuvers is high. Patients may have tenderness over the scalene muscles to palpation. Tapping above the clavicle (Tinel sign) may be positive by reproducing the symptoms.
Provocative testing includes the elevated arm stress test (“EAST Maneuver” or Roos test) whereby the patient is instructed to abduct the shoulders and flex the elbows 90 degrees while opening and closing the hands for 3 min. If positive, the patient should have difficulty as the time progresses in opening and closing the hands or keeping the arms elevated. Rotating the head and placing the ear to the shoulder may cause pain and paresthesias in the opposite upper limb, but this may also be positive in cervical radiculopathy. The modified Upper Limb Tension Test of Elvey (ULTT) involves having the patient abduct both shoulders to 90 degrees without elbow flexion, dorsiflex the wrists, and tilt the head to both sides. If paresthesias or pain occurs in the limb, it is considered positive. Although these tests may be helpful in the diagnosis of TOS, an extremely high rate of false positives may occur. A study from Plewa and Delinger demonstrated a false-positive rate for paresthesias of 15% with the EAST maneuver. A study from Davis et al. showed a false-positive rate of 86.9% for the ULTT.
Diagnostic Criteria and Testing
Imaging and diagnostic support of nTOS is not always clear ( Fig. 22.4 ). Because common conditions such as cervical disc degeneration may be seen on radiography and MRI of the cervical spine, it may be mistaken as the cause of the symptoms. Plain radiographs of the neck may reveal bony anomalies, such as a cervical rib, significantly enlarged C7 transverse process, evidence of a prior fracture/trauma to the clavicle, or calcification of the vasculature in the thoracic outlet, which would point more to vTOS or aTOS ( Fig. 22.5 ). Radiograph views include anteroposterior, lateral, oblique, flexion, and extension to assess for cervical spine pathology that is much more common than TOS.
MRI of the brachial plexus may show inflammatory changes but is often normal. MRI of the cervical spine is often performed to rule out a cervical disc herniation, significant foraminal narrowing, cervical spinal stenosis, or spinal cord compression. The MRI must be interpreted in the clinical context with a careful history and physical examination, as degenerative discs, spondylosis, and disc herniations may occur without clinical symptoms.
Electrodiagnostic testing is often normal in patients with TOS or may show subtle or vague abnormalities. If the lower trunk of the brachial plexus is involved, nerve conduction studies may demonstrate prolonged or absent F-waves in the median and ulnar nerves. In axonopathy, the compound muscle action potentials (CMAPs) may be reduced in the median and ulnar nerves. Classically, the median sensory nerve action potential (SNAP) is preserved as these fibers traverse the upper and middle trunks of the brachial plexus. However, the ulnar SNAP shows a reduction in amplitude as it passes through the lower trunk. The medial antebrachial cutaneous SNAP may be reduced or absent, as well.
Lesions involving the lower plexus are often more sensitive. In a retrospective study of patients with surgically confirmed true nTOS who had electrodiagnostic testing before surgery, Tsao et al. found a reduced median CMAP amplitude in the affected arm with 95% sensitivity.
Differentiating a C8 radiculopathy from nTOS can be challenging but may be aided by electrodiagnostic testing. In C8 or T1 radiculopathies, the ulnar and median SNAPs are maintained. In nTOS, the ulnar SNAP is often reduced.
The needle electromyography (EMG) study may show signs of denervation in the C8-T1 median and ulnar-supplied muscles. This would include the presence of fibrillations and/or positive sharp waves, the presence of polyphasic motor unit potentials (MUPs) upon voluntary activation, and possible reduction in recruitment on voluntary contraction (less available MUPs with a faster firing rate). Reduced recruitment is often the first abnormality seen and generally precedes F-wave and SEP (sensory evoked potentials) abnormalities. No studies have shown the sensitivity and specificity of EMG in the detection of nTOS.
Diagnostic scalene blocks may aid in the diagnosis of nTOS. As with any “diagnostic injection,” the possibility of a placebo response is of concern. The block is typically performed by injecting the anterior scalene with an anesthetic, such as lidocaine or bupivacaine, via ultrasound imaging, fluoroscopy, or CT-guidance. Patients should report significant decreased symptoms for the duration of the anesthetic. Using a “pain diary” where the patient reports the level of pain before injection and then once an hour for several hours helps in documenting the perceived reduction in symptoms. The test is often used in surgical planning and reports of up to 90% success with scalene resection with a positive diagnostic injection are quoted ( Fig. 22.6 ).
