Thoracic outlet syndrome (TOS) has three subtypes. Which subtype is the most common, accounts for >95% of cases, and is characterised by compression of the lower trunk/medial cord of the brachial plexus causing hand weakness and paraesthesias in a C8/T1 distribution?

• A Arterial TOS; due to subclavian artery compression by cervical rib
• B Neurogenic TOS; due to compression of the lower trunk of the brachial plexus ✓
• C Venous TOS (Paget-Schroetter syndrome); due to axillary-subclavian vein thrombosis
• D Mixed TOS; combined arterial and venous compression

Explanation

Neurogenic TOS accounts for >95% of all TOS cases and results from compression of the C8–T1 nerve roots or lower trunk of the brachial plexus between the anterior and middle scalene muscles or by a cervical rib/fibrous band. It presents with medial forearm and hand paraesthesias (ulnar distribution), intrinsic hand muscle wasting (thenar/hypothenar), and positive provocation tests (Adson's, Roos elevated arm stress test). Arterial TOS (<1%) and venous TOS (~5%) are far less common.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.