Thoracic Outlet Syndrome: Causes, Diagnosis, and Treatment

Pathophysiology

TOS pathophysiology involves compression of neurovascular structures at one or more of the three anatomic spaces of the thoracic outlet. Each space has distinct anatomic boundaries and specific compression mechanisms.

Anatomy of the thoracic outlet: interscalene triangle, costoclavicular space, and subcoracoid space — relationship of the brachial plexus, subclavian artery, and subclavian vein with the adjacent bony and muscular structures

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Interscalene Triangle

Bounded by the anterior scalene muscle (anteriorly), the middle scalene muscle (posteriorly), and the first rib (inferiorly). The brachial plexus and subclavian artery pass through this triangle. Scalene muscle hypertrophy — frequent in forward-head postures and in workers performing repetitive upper-limb movements — is the most common compression mechanism in this region.

Costoclavicular Space

Located between the inferior surface of the clavicle and the superior surface of the first rib. This space narrows with shoulder depression, carrying heavy bags or backpacks over the shoulders, or through bony anomalies (first-rib elevation, clavicular fracture callus). Exaggerated military posture (shoulders back and down) reproduces compression in this space.

Subcoracoid Space (Retropectoralis Minor)

Behind the pectoralis minor, near the coracoid process. Compression occurs during arm hyperabduction — overhead activities such as painting walls, throwing objects, or sleeping with arms raised. Chronic pectoralis minor shortening in protracted-shoulder postures worsens the compression.

Signs and Symptoms

TOS clinical presentation depends on which structure is compressed. Neurogenic TOS — accounting for 95% of cases — dominates the clinical picture, but the arterial and venous vascular types, although rare, require early recognition because of their potential for serious complications.

Neurogenic TOS

Brachial plexus compression predominantly affects the lower trunk (C8-T1 roots), causing symptoms on the ulnar side of the forearm and hand. Patients report pain, paresthesias (tingling, numbness), and hand weakness, often worsened by arms-raised activities.

Venous TOS (Paget-Schroetter Syndrome)

Subclavian vein compression can lead to effort venous thrombosis, known as Paget-Schroetter syndrome. The patient presents with sudden arm edema (swelling), cyanosis (bluish discoloration), heaviness, and visible venous distention in the upper limb and chest wall. It is more frequent in young individuals after vigorous physical effort.

Arterial TOS

Subclavian artery compression is the rarest type, but it has the greatest potential for complications. It presents with hand pallor and coldness, arm fatigue with exercise, upper-limb claudication, absent radial pulse during provocative maneuvers, and, in severe cases, distal thromboembolic events. It is strongly associated with a cervical rib.

Diagnosis

TOS diagnosis is predominantly clinical, based on detailed history and provocative tests. No single test definitively confirms neurogenic TOS, which contributes to the diagnostic controversy. Complementary exams help exclude alternative diagnoses and confirm the vascular types.

Roos test (EAST): patient with arms abducted to 90° and elbows flexed, opening and closing the hands for 3 minutes — provocative test for neurogenic TOS

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Differential Diagnosis

Neurogenic TOS is one of the musculoskeletal conditions with the broadest differential diagnosis, given the nonspecificity of many of its symptoms. The distinction is essential to avoid inappropriate treatments.

Treatments

Conservative treatment is the first line for neurogenic TOS, with success rates of 50 to 90% when performed adequately and consistently. The approach is based on postural correction, muscle stretching, neural mobilization, and scapular stabilization.

Surgical treatment (first-rib resection, scalenectomy) is reserved for vascular TOS, neurogenic TOS refractory to conservative treatment for 3-6 months, and cases with progressive hand muscle atrophy.

Medical Acupuncture in TOS

Medical acupuncture acts as a complementary therapy in the conservative treatment of neurogenic TOS, working through two main mechanisms: relaxation of the compressing musculature (scalenes and pectoralis minor) and modulation of brachial plexus neuropathic pain.

Needling points in the scalene region (lateral cervical territory) promotes local muscle relaxation through stretch reflex and acetylcholine release at the motor end plate, directly reducing compression in the interscalene triangle. Low-frequency electroacupuncture (2 Hz) applied to this region potentiates the muscle-relaxation effect.

For distal neuropathic symptoms (paresthesias, C8-T1 pain), points along the brachial plexus and ulnar nerve course — including points in the supraclavicular fossa, scapular region (SI-11 to SI-15), and distal points such as LI-4, TE-5 (SJ-5), and PC-6 — modulate nociceptive transmission and improve perineural circulation. Combining local points (in the compressive region) and distal points (in the upper limb) is the most widely used strategy.

Evidence for acupuncture in TOS comes predominantly from case reports and series, with favorable results in pain reduction, improved paresthesias, and increased tolerance to overhead activities. Large randomized controlled trials are still needed. Acupuncture is used as part of an integrated conservative approach — combined with exercise, postural correction, and ergonomic modification — not as an isolated treatment.

When to See a Doctor

Specialized medical evaluation is important to differentiate TOS from other causes of upper-limb pain and paresthesia. A pain physician, orthopedist, or acupuncture physician can perform the appropriate workup and establish the correct diagnosis.