Thoracic Outlet Syndrome

Thoracic outlet syndrome (TOS) is a poorly characterized disease entity with a wide differential diagnosis. First coined in 1956 by Peet et al, TOS can be categorized as vascular (arterial or venous) or neurogenic (NTOS). Although vascular-related TOS pathology is intuitively easier to understand and document because of more definitive imaging findings and symptoms, there remains significant controversy as to even the existence of NTOS.

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Thoracic Outlet Syndrome Summary

Thoracic outlet syndrome (TOS) is a frequently overlooked peripheral nerve compression that creates difficulties for the clinician regarding diagnosis and management. Diagnosing TOS can be challenging because the symptoms vary greatly amongst patients with the disorder. A careful history and thorough clinical examination are the most important components in establishing the diagnosis of TOS. Injection treatments can aid diagnosis and help recovery in patients who do not respond to conservative management.

Anatomic Issue

The anatomic issue in TOS occurs as the result of compression of the neurovascular bundle (brachial plexus, subclavian artery, and subclavian vein) at the transition between the neck and axilla just above the first rib. Neurogenic TOS is much more common than vascular TOS, with most single center series reporting ratios of 20 to 1. Symptoms of NTOS referable to the upper extremity occur because of compression of the lower trunk of the brachial plexus caused by a cervical rib or band and enlarged scalene muscles.

Classically described or “true” NTOS with strict diagnostic criteria was outlined by Gilliatt et al in 1974 , but unfortunately, most reported series of NTOS to date rarely meet these criteria. Symptoms typically include arm discomfort, paresthesias of the inner surface of the hand and forearm, and weakness and atrophy of the thenar and intrinsic hand muscles of the affected side. Distinct anatomic and electrophysiologic findings include low compound muscle action potentials in the thenar and intrinsic muscles, abnormal sensory conduction of the ulnar nerve, prolonged F-wave latency of the ulnar nerve, and abnormal sensory conduction of the medial antebrachial cutaneous nerve.

Pathophysiology Of Thoracic Outlet Syndrome

Post-traumatic Onset

The large majority of NTOS patients give a history of some type of hyper-extension neck injury preceding the onset of symptoms. Whiplash injuries in motor vehicle accidents is the most common cause, but other causes include falls on ice, slippery floors, or downstairs, and athletic injuries. In these patients the usual sequence of symptom development is neck pain within the first 24 h followed within a few days by headaches and pain over the trapezius muscles. Anywhere from a few days to a several weeks later pain moves into the upper extremities and paresthesia develop in the fingers and hands.

Putting the history of an injury together with the pattern of symptom development and subsequent muscle pathology, a plausible explanation for the pathophysiology emerges. Following such an injury the initial neck pain is due to two things: cervical spine neck strain and acute tearing of the scalene muscle fibers. There is probably some intramuscular hemorrhage which causes muscle swelling and increased neck pain over the first few days. The symptoms of arm pain and paresthesia that develop in the first few days are probably due to swelling of the injured scalene muscles. If the muscle injury is mild enough so that there is minimal swelling, arm pain and paresthesias may not appear for a few weeks. These later arm and hand symptoms are then due to the healing process within the scalene muscles as intramuscular blood is absorbed and replaced by fibroblasts and collagen, resulting in scarring and overly tight muscles. Since the nerve roots are usually in contact with the scalene muscles, when the muscles become scarred they compress the nerve roots. It should be stressed that even though these muscles appear normal when viewed during surgery, the microscopic picture is not. As discussed above, the predominance of type I and reduction of type II muscle fibers along with the significant fibrosis seen further confirms that there has been significant structural changes in the muscles.

In addition to the objective pathology described above, other lines of evidence further implicate the scalene muscles as the primary site of pathology in most cases. Scalene muscle block with local anesthetic can temporarily relieve symptoms. and reverse physical findings within a few minute of injection, and correlates well with outcomes.

Repetitive Stress Injury (RSI)

People who perform repetitive activities (especially with the hands and arms in an awkward or fixed position) such as keyboard entry, assembly line work, sitting in one spot for several hours at a time, or work in an intrinsically awkward position (dentists or hygenists  may also develop NTOS. In these patients multiple points of nerve compression are often seen, including problems at the carpal or cuboid tunnels and/or pectoralis minor insertion site.

Cervical ribs and anomalous first ribs

Cervical ribs arise from the transverse process of C7 and occur in about one in 140 people (0.7 %). They are more than twice as common in women than in men (70–30 %). Anomalous first ribs also have an incidence of 0.7 % and are equally as common in men as women. Cervical and anomalous first ribs are usually predisposing causes of NTOS. The majority of patients who posses them are asymptomatic. When symptoms of NTOS occur, it is usually following some type of hyperextension neck injury.

Clinical Presentation Of Patients With Ntos

Classically, the positive fi ndings that suggest NTOS include a history of tingling, deadness, or weakness in the upper extremity which are exacerbated by maneuvers that compromise the thoracic outlet (arms overhead) or stretch the plexus (dangling). Similar findings may be elicited by bedside maneuvers that simulate a patient’s experience. Pulse obliteration with arm abduction may be found to suggest combined neural and vascular compromise through the thoracic outlet. Actual muscle atrophy may occur on rare occasion. Sensitivity to palpation of the neural elements may be found in the supraclavicular fossa or over the pectoralis tendon insertion.

Neurological symptoms affected by position

The presence of a history of positional paresthesias with reaching overhead, although suggestive of NTOS, is nonspecific. Nocturnal numbness, which is often reported by NTOS patients, is also a common complaint in patients with carpal tunnel syndrome and ulnar compression neuropathy. Patients with NTOS may also report worsening of symptoms with dangling of the arm when walking.

Pulse obliteration with arm hyperabduction

Pulse obliteration may be observed with arm hyperabduction in patients with NTOS, although this finding alone is very common in normal individuals.

Stress maneuver reproduction of symptoms

Stress maneuvers have been described to reproduce those positional and effort related activities that may produce a sensory experience that is historically familiar to the patient.

Elevated Arm Stress Test (EAST)

Although a 3 min test was classically described by Roos, a 1 min stress test (1 min EAST) may be considered because many patients with NTOS will have marked symptoms within a few seconds.

Adson test

The Adson maneuver is performed by having the patient turn their head toward the pathologic side as the patient inhales with the arm extended; classically described to look for pulse changes, many use it to assess whether neurologic symptoms are exacerbated.

Problems In Diagnosing Thoracic Outlet Syndrome

The controversy in the diagnostic workup for patients with suspected NNTOS emanates from the fact that the presentation can be varied and overlaps with many other musculoskeletal issues of the upper extremities. Patients will typically have a history of a hyperextension neck injury, such as whiplash from an automobile accident or a fall to the floor. Also very common is a work-related injury caused by repetitive movements. Predisposing anatomic factors to NNTOS include cervical ribs, anomalous first ribs, and congenitally narrowed scalene triangles. Another common presentation is athletes with repetitive upper limb movements, including swimmers, divers, water polo players, rowers, baseball pitchers, and football quarterbacks . Certainly, this very heterogeneous group of presenting patients will have a wide differential diagnosis, including and not limited to cubital and carpal tunnel syndromes, myofascial pain syndromes, and spinal stenosis.


The clinical diagnosis of NTOS remains controversial and challenging. Fortunately, modern medical imaging, particularly MRI, provides excellent evaluation of the brachial plexus, the surrounding soft tissues and bones, and the dynamic changes that occur in the thoracic outlet on movement of the upper extremity.

MRI or CT should be performed with the patient’s arms in the neutral position, and then with the arms in hyperabduction-external rotation. The volume of imaging should extend from the cervical spine medially to the axilla laterally. Sagittal and axial MRI images are usually sufficient.

The primary goal of any imaging test intended to diagnose NTOS is to assess for impingement on the brachial plexus or its components. The first step is to evaluate the course of the brachial plexus. looking for abnormalities of each of the anatomic tunnels in turn, and for impingement on the brachial plexus caused by those entities. Evaluation of the brachial plexus should include any intrinsic lesion of the brachial plexus. The next step is to evaluate the hyperabductionexternal rotation images. Evaluation of the cervical spine to rule out central canal or neural foraminal stenosis, and of the lung apices and supraclavicular fossa soft tissues to rule out a soft tissue mass involving the brachial plexus should be performed.

Finally, MR angiography should be considered, as there is frequently an element of vascular compression in patients with brachial plexus compression.

Scalene Test Block

Sclene muscles opt 1A scalene test block is designed to provide diagnostic information that would help a clinician decide on a therapy that targets NTOS specifically. A scalene test block is designed for the purposes of temporarily reversing the TOS component for a few hours in order to demonstrate a resulting substantial improvement in the performance of activities that would typically be limited by pain, rapid development of fatigue or numbness. In this manner, the patient and clinician is able to preview what may happen after targeted therapy is applied so that NTOS decompression surgery may be considered with a greater degree of confidence.

Scalene test block is able to produce a temporary relief by virtue of producing temporary paralysis of the muscle due to anesthetic blockade at the level of the intramuscular nerve branches. Potential direct effects of muscle paralysis include relaxation of neurovascular compression between tightened muscles at the interscalene triangle as well as potential dropping of the top rib while upward tension is lost from the scalene muscle. Other direct effects may result from blockade of painful sensory input from the muscles. Indirect effects that may confound analysis include placebo effects and examiner biases which both need to be minimized.

Occasionally weeks or months of therapeutic benefit may result from scalene test injections, although the procedure is designed primarily for diagnostic purposes.

The target muscles include the anterior scalene, subclavius and pectoralis minor.

Botulinum Toxin Injections

Botulinum toxin injections can be used in management of TOS. The most commonly targeted muscle is anterior scalene but full decompression of the thoracic outlet may require chemodenervation of muscles distal to the scalenes. Patients who already had scalenectomy could still achieve relief with botulinum injections of the subclavius and pectoralis minor muscles.

Ultrasound Guided Scalene Blocks

Ultrasound allows precise depiction of anterior scalene muscle and intramuscular needle placement in all patients. Furthermore, real-time delivery of medication is visualized, increasing the certainty of intramuscular delivery of the drug.

Surgical Treatment

Thoracic outlet decompression is appropriate for patients who have a sound clinical diagnosis of NTOS and have failed to improve with physical therapy, particularly for those who have had a positive response to an anterior scalene and/or pectoralis minor muscle block. Surgical options include pectoralis minor tenotomy; supraclavicular decompression with scalenectomy, brachial plexus neurolysis and first rib resection; or a combined procedure that includes both supraclavicular decompression and pectoralis minor tenotomy.

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Dr Murli Krishna

Consultant Pain Medicine