Challenges in the Treatment of Thoracic Outlet Syndrome

Thoracic outlet syndrome (TOS) represents a group of heterogeneous and potentially disabling upper-extremity disorders that are caused by extrinsic compression of neurovascular structures between the first rib and clavicle. There are 3 distinct types of TOS, which are classified according to the principal anatomic structures involved and the clinical syndromes that result: neurogenic TOS, venous TOS, and arterial TOS. All 3 forms of TOS are rare, but they are clinically important because, when unrecognized or inadequately treated, they can cause chronic pain syndromes, long-term restrictions in use of the upper extremities, limb-threatening complications, and substantial disability even in relatively young, active, and otherwise healthy individuals. Accurate diagnosis of TOS can be a substantial challenge in practice, because of a lack of physician awareness, clinical features that overlap or mimic more common conditions, and an absence of clearly defined (objective) diagnostic criteria. There is also persistent controversy regarding the efficacy of the various treatment approaches for TOS—approaches that vary in accordance with the experience, expertise, and specialty of the physician. The purpose of this presentation is to briefly review current protocols for the diagnosis and treatment of TOS and to highlight the clinical-management challenges that remain.

Neurogenic Thoracic Outlet Syndrome

Neurogenic TOS constitutes 85% to 90% of TOS cases and is characterized by compression and irritation of the brachial plexus nerve roots (C5 to T1).¹ The site of neural compression is typically within the scalene triangle at the level of the first rib but can also occur within the subcoracoid space underneath the pectoralis minor muscle tendon. Neurogenic TOS is caused by a combination of congenital variations in anatomy—such as anomalous scalene musculature, aberrant fascial bands, or cervical ribs—coupled with injury that has resulted in scalene muscle spasm, fibrosis, or other pathologic changes.

Neurogenic TOS most frequently occurs in relatively young and otherwise healthy individuals, particularly in those engaged in heavy lifting or repetitive overhead use of the upper extremities; it is often associated with protracted delays in diagnosis and a history of previous surgical and nonsurgical treatments. The symptoms of brachial plexus nerve root compression consist of pain, numbness, and paresthesia affecting the neck, upper back, shoulder, arm, and hand. These symptoms can be somewhat variable but are typically dynamic, with marked positional exacerbation during arm elevation. Consistent physical examination findings include localized tenderness to palpation over the supraclavicular or subcoracoid space, with reproduction of radiating upper-extremity symptoms and exacerbation of those symptoms during positional upper-extremity maneuvers, such as the 3-minute elevated arm stress test (EAST).

Because patients with neurogenic TOS usually exhibit normal or nonspecific findings on conventional electrophysiologic testing or imaging studies, neurogenic TOS is typically diagnosed on the basis of positive clinical findings and the exclusion of other conditions.² The mainstay of initial treatment is conservative management, grounded in physical therapy, muscle relaxants, anti-inflammatory agents, and adjustments in workplace ergonomic factors. Symptoms might not improve in patients who have substantial or long-standing disabilities. However, properly identified and selected patients can respond quite well to surgical treatment, consisting of scalenectomy, brachial plexus neurolysis, and first-rib resection.³

There are still many unresolved issues related to neurogenic TOS. These include the precise pathophysiologic mechanisms involved, diagnostic criteria to differentiate neurogenic TOS from other cervical–brachial syndromes, prognostic criteria for selection of patients for different forms of treatment, outcomes that can be expected after different types of surgical and nonsurgical treatment, and methods to reduce symptomatic recurrence.

Venous Thoracic Outlet Syndrome

Venous TOS (10%–15% of TOS cases) is caused by subclavian vein compression between the clavicle and first rib within the costoclavicular space, resulting in the abrupt presentation of axillary–subclavian vein effort thrombosis (Paget-von Schroetter syndrome). This condition is characterized by spontaneous swelling of the entire arm, often with cyanotic discoloration, heaviness, and pain.⁴ The pathogenesis of effort thrombosis is not an underlying coagulation disorder; rather, it involves repetitive extrinsic compression of the subclavian vein between the clavicle, first rib, subclavius muscle, and costoclavicular ligament. In particular, activities that involve arm elevation or heavy exertion can result in chronic injury and progressive fibrous stenosis, collateral vein expansion, and eventual thrombotic occlusion.

Conservative treatment of subclavian-vein effort thrombosis, consisting of anticoagulation and arm elevation, is associated with a notable prevalence of chronic venous congestion, particularly when the arm is used actively, as well as with the limitations and restrictions that are imposed by long-term anticoagulation. Current management approaches to venous TOS therefore emphasize early contrast venography and catheter-based thrombolytic therapy, followed (after a variable interval) by surgical thoracic outlet decompression.

The vast majority of patients with recent axillary–subclavian vein effort thrombosis are excellent candidates for surgical treatment as definitive management, particularly within the first several weeks of undergoing successful thrombolytic therapy. Surgery usually consists of transaxillary or paraclavicular first-rib resection, and it might be accompanied by either endovascular management (balloon angioplasty) or direct venous reconstruction (patch angioplasty or bypass) for residual subclavian vein obstruction.⁵ Excellent results have been reported for all of these surgical approaches. However, unresolved issues regarding venous TOS include earlier detection and prompt referral to a specialist for treatment, the timing and methods used for thrombolysis, the type and extent of surgical treatment needed to achieve optimal long-term functional outcomes, and the need for adjunctive treatments such as chronic anticoagulation.

Arterial Thoracic Outlet Syndrome

Arterial TOS (2%–5% of TOS cases), usually found in association with an anomalous cervical rib, is caused by subclavian artery compression within the scalene triangle, which leads to the development of poststenotic subclavian aneurysms. In athletes who habitually elevate their arms, the axillary artery might be compressed at the level of the pectoralis minor tendon opposite the humeral head, which has similar pathologic consequences.⁶ These lesions are often accompanied by mural thrombus formation and are frequently complicated by distal thromboembolism manifested by hand or digital ischemia. The need for anticoagulation and urgent surgical treatment is undisputed in patients with acute ischemia. Unresolved questions pertain to the early detection of arterial TOS and the indications for surgical treatment of small subclavian or axillary artery aneurysms, to the exact surgical techniques needed to obtain optimal results, and to the role of adjunctive therapies for digital vasospasm and reflex sympathetic dystrophy (complex regional pain syndrome) that can accompany this condition.

Although arterial TOS is considered a mechanical problem related to extrinsic compression, it can be associated with a propensity for thrombosis and thromboembolism that can limit the success of treatment. Early diagnosis and prompt surgical treatment are therefore crucial.