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Once a poorly understood and heavily debated disease within cardiovascular medicine, thoracic outlet syndrome (TOS) has recently been recognized as a more common syndrome than previously thought.1 The condition has many presentations, including vascular and neurogenic, but it is hypothesized that the common pathophysiology of TOS is due to a narrowing of the thoracic outlet.

The thoracic outlet is defined by an area through which the subclavian vein, subclavian artery, and brachial plexus all emerge as a neurovascular bundle. Anatomically, the outlet is defined superiorly and inferiorly by the clavicle and first rib, respectively; this area is called the costoclavicular space. The subclavian artery and brachial plexus emerge between the anterior and posterior scalene muscles, and the subclavian vein runs anterior to the anterior scalene muscles into the outlet from which they all continue distally into the arm.

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There are numerous conditions that can lead to a narrowing of this space, including congenital bone and muscle anomalies, repetitive trauma, stress, depression, and poor posture.1 One study showed that 29% of patients with TOS have bone anomalies.2 Another study found that 43% of patients who received surgical correction for their TOS had an anomaly of scalene muscle development and/or muscle insertion, whereas only 8.5% had an anomalous cervical rib.3

Subacute upper extremity presentations

TOS is further subdivided into neurogenic, venous, and arterial subtypes, dependent on which structures become impinged within the outlet. The neurogenic type (nTOS) is the most common, and presents in approximately 95% of patients diagnosed with TOS. The venous subtype (vTOS) is present in 3% to 5% of patients. The arterial subtype (aTOS) is the most rare, comprising only 1% to 2% of presentations of those with TOS.1 Although the different types share a common pathophysiology of a narrowed outlet space, their clinical presentations differ widely and should be considered in unilateral presentations of subacute upper extremity complaints in primary care offices.

The following discusses nTOS, vTOS, and aTOS, and their diagnosis and clinical management.

Which of the following is the most frequently presenting cause of thoracic outlet syndrome among your patients?

Neurogenic TOS

Some physicians further subdivide nTOS patients based on where the brachial plexus becomes impinged.4 Those who advocate this philosophy distinguish impingement between the scalene muscles as an upper thoracic syndrome—also called cervical outlet syndrome—and impingement between the first rib and clavicle as a true thoracic outlet syndrome.5 Patients with nTOS most commonly present with symptoms of intermittent pain, numbness, and tingling on the ipsilateral side that are distributed in the arms, hands, and fingers. Cervical nTOS has a distribution between C5 and C7, whereas true nTOS has a distribution between C8 and T1.4,5 With regard to what causes nTOS, one study showed that 50% of nTOS patients have a history of repetitive trauma to the shoulder area, which is hypothesized to result in inflammatory changes and narrowing of the thoracic outlet.1

Even though nTOS is the most common subtype of TOS, the clinical evaluation for patients presenting with nTOS is the most poorly correlated of the three subtypes. However, there are two tests that can raise suspicion for TOS: the elevated arm stress test (EAST) and a lidocaine scalene block test.

A patient who presents with symptoms of TOS and a history of repetitive trauma to the shoulder should have an EAST examination to evaluate for nTOS. The EAST examination is performed by having the patient abduct the shoulder to 90° with the elbow flexed to 90° and then place his or her hands facing forward while opening and closing the hands for 3 minutes. A positive test result occurs when the observer sees a decrease in the ability to open and close the hand or a lowering of the patient’s arm with increased time in opening and closing the hand.1 The test is not very specific; however, with a thorough patient history, the test result may support further evaluation for nTOS.

One test that has historically been helpful in diagnosis of nTOS is the lidocaine scalene block test. With imaging guidance, the anterior scalene is injected with lidocaine; in patients with nTOS, a decrease to near resolution of symptoms for up to 4 hours is observed. The lidocaine block test has had a positive predictive value of 90% for success in patients receiving further treatment.6

Initial management for nTOS patients is nonoperative and consists of physical therapy and lifestyle modifications. Successful modifications include avoidance of aggravating behaviors, ergonomic modifications, and selective use of some pharmacologic agents, including nonsteroidal anti-inflammatory drugs, antidepressants, and muscle relaxants, with 60% to 70% of patients reporting resolution of symptoms.1 If 8 to 12 weeks of nonoperative management fails, patients may subsequently need to seek referral for surgical management options.