Thoracic Outlet Syndrome
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Direct answer
Ninety-five per cent of thoracic outlet syndrome is neurogenic — the lower trunk of the brachial plexus (C8–T1) is compressed between the scalene muscles, the first rib and the clavicle, producing medial arm and forearm paraesthesia with wasting of the intrinsic hand muscles, classically in a young woman with a cervical rib or drooping shoulders. Venous thoracic outlet (Paget-Schroetter syndrome, effort thrombosis of the subclavian vein) presents as a swollen blue arm in a young athlete after repetitive overhead activity; arterial compression, the rarest, comes from a bony anomaly (cervical rib, anomalous first rib) causing post-stenotic subclavian aneurysm with distal embolism. Neurogenic disease is treated conservatively first with 3–6 months of physiotherapy, reserving first rib resection (with scalenectomy, usually transaxillary or supraclavicular) for failure; venous and arterial forms are surgical diseases — thrombolysis or embolic management followed by decompression.
What you must remember
- The cervical rib (present in under 1 per cent of the population, mostly asymptomatic) compresses the lower trunk and subclavian artery; a fibrous band from a rudimentary cervical rib can compress without a visible bony rib on plain films.
- Neurogenic features: aching arm worse with overhead use, paraesthesia in the ulnar distribution (medial forearm — a key discriminant from carpal tunnel), and late wasting of the thenar or intrinsic hand muscles (C8–T1).
- Provocation tests: Roos (elevated arm stress test, 3 minutes of opening and closing fists with arms abducted — the most useful), Adson's (loss of radial pulse with deep inspiration, head turned to the affected side — high false-positive rate), Wright's hyperabduction and costoclavicular manoeuvre.
- Paget-Schroetter syndrome: spontaneous axillary-subclavian deep vein thrombosis from effort in young athletes; treat with catheter-directed thrombolysis, then first rib resection to remove the extrinsic compression, with anticoagulation bridging.
- Nerve conduction and EMG are frequently normal in early neurogenic TOS — a normal study does not exclude the diagnosis; plain chest/neck X-ray or CT identifies bony anomalies, and venous or arterial duplex plus CT angiography/venography stages vascular forms.
Approach to diagnosis walked through
A 28-year-old badminton player reports six months of numbness along the medial forearm and little finger, worse after long matches, with recent difficulty buttoning shirts. The examination plan: inspect for shoulder droop and a supraclavicular fullness; palpate the supraclavicular fossa for a bony rib and for Tinel-like brachial plexus tenderness; test the hand for thenar and interosseous wasting; check pulses at rest. Then provocation: the Roos test — arms abducted 90 degrees, elbows flexed, fists opened and closed for three minutes — reproduces her symptoms and unmasks hand fatigue, which is far more persuasive than a transient pulse change on Adson's. Next, exclude mimics: cervical spine X-rays or MRI for disc disease (C8–T1 radiculopathy), nerve studies for carpal tunnel and ulnar neuropathy at the elbow — remembering that ulnar neuropathy spares the medial forearm, whereas TOS does not, because the medial antebrachial cutaneous nerve travels with the plexus. A neck/chest radiograph shows a right cervical rib. Because she is neurogenic and has had only three months of symptoms, the answer is a structured 3–6 month physiotherapy programme — shoulder girdle strengthening, posture correction, avoidance of overhead loading — which helps the majority. If meaningful symptoms persist despite a genuine conservative trial, supraclavicular or transaxillary first rib resection with release of the scalenes and any fibrous band is offered.
Where students slip
The commonest error is calling every hand paraesthesia thoracic outlet syndrome without a distribution check: carpal tunnel is median (thumb to radial half of ring finger) and spares the palm; TOS is C8–T1 and always involves the medial forearm. The second is treating a positive Adson's test as diagnostic — pulse disappears with head turning in many normal people, so it is a clue, never proof. In the viva, the trap question is the swollen blue arm of the young cricketer: the expected answer is Paget-Schroetter effort thrombosis, thrombolysis followed by first rib resection — not lifelong anticoagulation alone, which leaves the compressive anatomy in place.
Frequently asked questions
Which is the commonest type of thoracic outlet syndrome?
Neurogenic (around 90–95 per cent), from lower trunk C8–T1 compression; vascular (venous or arterial) forms are far less common.
Which provocation test is most useful for neurogenic TOS?
The Roos elevated arm stress test — symptom reproduction within three minutes of repetitive fist clenching with arms abducted; Adson's test lacks specificity.
What is Paget-Schroetter syndrome?
Effort-induced axillary-subclavian vein thrombosis in young athletes with underlying venous compression; treat with catheter-directed thrombolysis followed by first rib resection.
Why can neurophysiology be normal in thoracic outlet syndrome?
Compression is often intermittent and positional, so distal conduction studies remain normal until chronic axonal loss develops — a normal EMG does not exclude the diagnosis.
How is a cervical rib related to subclavian aneurysm?
Chronic compression between the rib and first rib or scalene band produces post-stenotic dilatation, which then harbours thrombus and showers distal emboli — decompression plus aneurysm repair is required.
Which cervical rib-related lesion produces distal emboli?
A post-stenotic subclavian aneurysm from chronic compression — it harbours thrombus and showers digital emboli, and needs decompression plus aneurysm repair.