skip to main content

Third Nerve Palsy – Aberrant Regeneration Red Flag — SCE Neurology MCQ

Instant feedback + full explanation. One question, done properly.

HardNeuro-ophthalmologyThird Nerve Palsy – Aberrant Regeneration Red FlagSCE Neurology

A 50-year-old man with longstanding diabetes develops a unilateral painless pupil-sparing third nerve palsy. His symptoms resolve spontaneously over 8 weeks. Six months later, aberrant regeneration is noted — the ptotic eyelid retracts on downgaze, and the pupil constricts on attempted adduction. What does the presence of aberrant regeneration signify?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Aberrant regeneration does NOT occur after microvascular third nerve palsy — its presence should prompt investigation for a compressive lesion (aneurysm, tumour)

Aberrant regeneration of the third nerve (misdirection of regenerating axons) does NOT occur after microvascular (ischaemic) third nerve palsy because the neural architecture is preserved (the lesion is demyelinating/ischaemic, not axonal). The presence of aberrant regeneration (lid retraction on downgaze, pupil constriction on adduction — 'pseudo-Argyll Robertson pupil') indicates prior axonal damage and should raise concern for a compressive lesion (PComA aneurysm, meningioma, or other mass). This requires urgent imaging. A: Aberrant regeneration should not follow microvascular palsy. C: MG has fatigable weakness, not aberrant regeneration. D: Diabetes causes microvascular, not compressive damage. E: Not a normal variant.

Reference: ABN Neuro-ophthalmology Guidelines