Thoracic Outlet Syndrome (TOS)

What is it?

The brachial plexus and subclavian artery/vein are compressed within the thoracic outlet (the space between the clavicle and first rib).

Commonly affected: Lower trunk of the brachial plexus (C8–T1), subclavian artery/vein.

How it develops

1. Anatomic narrowingA cervical rib, muscle hypertrophy, or poor posture narrows the outlet.
2. Neural compression (neurogenic type)Brachial plexus compression causes arm numbness, pain, and weakness.
3. Vascular compression (vascular type)Subclavian artery compression produces pallor, coolness, and Raynaud-like phenomenon in the hand.

Symptoms

• Worse with arm elevationSymptoms worsen with overhead activity or arm elevation.
• Arm numbness / painNumbness throughout the arm or hand (especially the 4th–5th fingers).
• Hand pallor / cyanosisIn the vascular type, the hand becomes pale or bluish on arm elevation.
• WeaknessReduced grip strength and impaired fine hand motor function.

How it is examined

• Adson testPositive if the radial pulse diminishes when the head is rotated to the affected side during deep inspiration.
• ROOS test (EAST)Arms abducted to 90° while opening and closing the hands for 3 minutes — reproduces symptoms if positive.
• Wright testHyperabduction of the arm reduces the radial pulse or reproduces symptoms.

Imaging

X-ray is used to detect a cervical rib.

• Presence or absence of a cervical rib
• First-rib abnormalities
• Clavicular deformity

MRI/MRA delineates the site and degree of neurovascular compression.

• Site of brachial plexus compression
• Vascular stenosis (on MRA)
• Surrounding muscular or structural abnormalities

When surgery is considered

Failure of 3–6 months of conservative therapy or severe vascular symptoms.

Procedures that may be discussed

• First-rib resection
• Cervical-rib resection (when present)
• Scalenectomy

Outlook

60–70% improve with physical therapy; 70–80% satisfaction after surgery.