According to Semon's law, in a progressive organic lesion of the recurrent laryngeal nerve, which fibres are affected first?

• A Only sensory fibres, leaving motor function intact
• B Abductor fibres, so adduction is lost before abduction
• C All fibres equally, producing immediate cadaveric position
• D Adductor fibres, so abduction is lost before adduction ✓

Explanation

Semon's law states that in progressive recurrent laryngeal nerve palsies, the abductor fibres of the nerve are affected earlier than the adductor fibres, so the cord lies near the midline and moves on phonation but fails to abduct. This explains why a unilateral palsy causes hoarseness without airway compromise, as the paralysed cord remains adducted. The law is a clinical rule rather than a strict histological fact, but it remains the conventional teaching in Indian exams.

Reference: Dhingra's Diseases of Ear, Nose and Throat, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.