In thoracic outlet syndrome (TOS) causing neurogenic compression of the lower trunk of the brachial plexus (C8–T1), which of the following findings is MOST characteristic?
- A Weakness and wasting of intrinsic hand muscles (thenar and hypothenar) with medial forearm sensory loss ✓
- B Wrist drop and weakness of wrist extension
- C Loss of elbow flexion and biceps wasting
- D Loss of shoulder abduction and external rotation
Correct answer: A. Weakness and wasting of intrinsic hand muscles (thenar and hypothenar) with medial forearm sensory loss
Explanation
The lower trunk of the brachial plexus (C8–T1) forms the medial cord, which contributes to the ulnar nerve and the medial head of the median nerve. Lower trunk compression in TOS causes: weakness and wasting of intrinsic hand muscles (both thenar medial portion via median C8–T1, and hypothenar via ulnar), sensory loss over the medial forearm (medial cutaneous nerve of the forearm, T1) and ring/little fingers. Wrist drop suggests radial nerve (posterior cord, C7). Loss of shoulder abduction/external rotation suggests upper trunk (C5–C6 — Erb's palsy).
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.