A 50-year-old woman with carpal tunnel syndrome has wasting of the thenar muscles and impaired opposition of the thumb. On testing, light touch and two-point discrimination over the skin of the central palm and thenar eminence are completely normal. What is the anatomical basis for this preservation?
- A The palmar skin is supplied by the recurrent motor branch rather than sensory fibres
- B The palmar cutaneous branch of the median nerve arises proximal to the flexor retinaculum and passes superficial to it ✓
- C Palmar skin is supplied by branches of the ulnar nerve arising in Guyon canal
- D Digital branches regenerate faster than motor branches after compression
Correct answer: B. The palmar cutaneous branch of the median nerve arises proximal to the flexor retinaculum and passes superficial to it
Explanation
The palmar cutaneous branch of the median nerve leaves the parent trunk roughly 5 cm proximal to the wrist, crosses the flexor retinaculum superficially, and supplies the central palmar skin. Because it never enters the carpal tunnel, its territory is spared even in advanced compression. This sparing localises the lesion to the tunnel itself rather than a proximal median nerve injury.
Reference: Moore's Clinically Oriented Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.