Thoracic Outlet Syndrome

Thoracic outlet syndrome is compression of the brachial plexus, subclavian artery or subclavian vein as they cross the superior thoracic aperture and pass over the first rib into the axilla. Three forms exist, and they differ in mechanism, population and urgency.

• Neurogenic (90 to 95%): compression of the lower trunk or medial cord. It is commoner in women (3 to 4:1), with onset between 20 and 50 years.
• Venous (3 to 5%): compression of the subclavian vein at the costoclavicular space, with effort thrombosis (Paget-Schroetter syndrome). It affects young, active men, often after repetitive overhead activity such as swimming, baseball or weightlifting.
• Arterial (1 to 2%): subclavian artery compression, usually from a cervical rib or anomalous first rib, with post-stenotic dilatation, aneurysm, mural thrombus and distal embolisation.

Anatomical sites of compression

• Interscalene triangle: anterior scalene, middle scalene and first rib. It contains the plexus and subclavian artery.
• Costoclavicular space: clavicle, first rib and subclavius muscle. It contains the vein, artery and plexus.
• Retropectoralis minor space: beneath the coracoid insertion of pectoralis minor.

Predisposing factors

• Bony: cervical rib (0.5 to 1% of people, usually asymptomatic), elongated C7 transverse process, anomalous first rib, clavicle malunion or callus after fracture.
• Soft tissue: fibromuscular bands (such as the Roos bands), scalene hypertrophy, scalenus minimus, and posttraumatic scarring after whiplash.
• Functional: poor posture with drooping shoulders, obesity, large pendulous breasts, and repetitive overhead work.

Disputed neurogenic thoracic outlet syndrome refers to pain and paraesthesia without objective electrodiagnostic abnormality. True neurogenic thoracic outlet syndrome has objective motor wasting and neurophysiological change, and is rare.

Neurogenic

• Pain and paraesthesia in the neck, shoulder, medial arm and forearm and ulnar hand (C8 to T1), worsened by overhead activity, carrying loads or prolonged driving.
• Hand weakness and clumsiness, with the Gilliatt-Sumner hand in true cases: wasting of the thenar eminence more than the hypothenar eminence and first dorsal interosseous, with sensory loss over the medial forearm.
• Occipital headache and trapezius spasm. Upper plexus patterns (C5 to C7) are less common and give neck and shoulder pain with lateral arm paraesthesia.

Venous

• Sudden swelling, heaviness and blue discolouration of the arm after exertion, with distended superficial veins over the shoulder and chest wall.
• Dull ache and warmth. Pulmonary embolism is uncommon (under 10%).

Arterial

• Arm claudication, coldness, pallor and Raynaud phenomenon, and a supraclavicular bruit or pulsatile mass.
• Digital ischaemia, splinter haemorrhages and acute limb ischaemia from embolisation.

Provocative tests

• Elevated arm stress test (Roos): hands held at 90 degrees abduction and external rotation, opening and closing the fists for 3 minutes. Reproduction of symptoms or heaviness is the most sensitive test.
• Adson, Wright and costoclavicular manoeuvres cause loss of radial pulse, but the pulse changes in many healthy people, so they are not diagnostic alone.
• Upper limb tension test and tenderness over the anterior scalene.

Red flags: pallor, pulselessness, rapid swelling, tissue loss, progressive wasting, and a known Pancoast tumour or prior neck radiation.

Differential diagnosis: cervical radiculopathy (neck-movement pain, Spurling positive), carpal tunnel syndrome, ulnar neuropathy at the elbow, rotator cuff disease, neuralgic amyotrophy, brachial plexopathy from tumour or radiation, complex regional pain syndrome, and upper limb deep vein thrombosis from a central catheter.

Neurogenic

• Clinical diagnosis supported by electrodiagnostic testing:
• Reduced medial antebrachial cutaneous and ulnar sensory potentials.
• Reduced median motor amplitude (abductor pollicis brevis) with neurogenic changes on needle EMG in C8 to T1 muscles, and a normal median sensory response (distinguishing it from carpal tunnel syndrome).
• Cervical spine and chest radiograph for cervical rib, C7 transverse process length, and first rib or clavicle anomalies. Apical lung lesions need CT chest.
• MRI of the cervical spine to exclude radiculopathy, and MR neurography or high resolution ultrasound to show plexus signal change and compressive bands.
• Diagnostic anterior scalene block under ultrasound guidance with 3 to 5 mL of bupivacaine 0.25% or lidocaine 1% shows more than 50% relief of symptoms within 30 minutes in responders, and predicts surgical benefit.

Venous

• Duplex ultrasound of the subclavian, axillary and internal jugular veins (absent compressibility, reduced respiratory phasicity).
• CT venography or contrast venography, with provocative positioning (arm abduction), is the definitive study and shows the extrinsic compression and collaterals.
• Thrombophilia screening is not routine, since the mechanism is mechanical.

Arterial

• Duplex with provocative manoeuvres, CT angiography or MR angiography in neutral and abducted positions, showing stenosis, post-stenotic aneurysm, mural thrombus and distal emboli.
• Echocardiography and rhythm monitoring to exclude other embolic sources, and Allen test with digital pressures for ischaemia.

Neurogenic thoracic outlet syndrome

• Initial conservative treatment for 3 to 6 months, successful in about half: physiotherapy to stretch the scalenes and pectoralis minor, strengthen scapular stabilisers, correct posture and avoid overhead work or heavy bags.
• Analgesia: naproxen 500 mg twice daily for short courses, gabapentin 300 mg at night titrated to 1800 mg/day, pregabalin 75 to 150 mg twice daily, or amitriptyline 10 to 50 mg at night.
• Botulinum toxin type A injected into the anterior scalene or pectoralis minor under ultrasound or EMG guidance (10 to 25 units per muscle) gives temporary relief, and a response supports the surgical indication.
• Surgery is indicated for persistent disabling symptoms despite 3 to 6 months of therapy, objective motor wasting, or a cervical rib with neurological deficit: first rib resection with anterior and middle scalenectomy and neurolysis through a transaxillary, supraclavicular or infraclavicular route. Cervical ribs and bands are excised at the same time. Pectoralis minor tenotomy is added for retropectoralis compression.
• Outcomes: 70 to 90% satisfaction in carefully selected patients. Complications are pneumothorax, phrenic nerve palsy, long thoracic nerve injury, brachial plexus injury, chylothorax and recurrence from residual rib stump (5 to 15%).

Venous thoracic outlet syndrome

• Start therapeutic anticoagulation: apixaban 10 mg twice daily for 7 days then 5 mg twice daily, or enoxaparin 1 mg/kg twice daily. Elevate the arm.
• For acute thrombosis within 14 days, catheter-directed thrombolysis with alteplase 0.5 to 1 mg/h by multi-sidehole catheter, with or without pharmacomechanical thrombectomy, restores patency in over 90%.
• First rib resection with scalenectomy and costoclavicular decompression after lysis, ideally within 2 to 12 weeks, because residual compression predicts rethrombosis. Perform venoplasty or open venolysis for residual stenosis. Stenting alone before decompression has high failure and is avoided.
• Continue anticoagulation for 3 months in total, longer if residual thrombus persists, with duplex follow-up at 1, 3 and 6 months.

Arterial thoracic outlet syndrome

• Urgent treatment for embolisation: heparin 80 units/kg IV bolus then 18 units/kg/h, thrombolysis or embolectomy for acute ischaemia.
• Definitive surgery for all symptomatic patients: resection of the cervical rib or first rib, with arterial reconstruction (interposition graft with vein or prosthetic material for aneurysm, endarterectomy and patch for stenosis). Sympathectomy may help for distal ischaemia.
• Antiplatelet therapy with aspirin 75 to 100 mg daily after reconstruction, with duplex at 1, 6 and 12 months.

Supportive care

• Occupational modification, ergonomic review, weight management, graded return to sport after surgery, and rehabilitation for 6 to 12 weeks after rib resection.
• Pain management with a multidisciplinary pain team in refractory neurogenic disease.