Ophthalmology · UKMLA & AKT

Diabetic cranial nerve palsies

A free high-yield preview for the UKMLA Applied Knowledge Test. Below are the key points to recognise diabetic cranial nerve palsies — the full SA Note notes add investigations, management, complications and 10 practice questions.

Key high-yield points

  • Diabetes causes microvascular ischaemia of the vasa nervorum → focal axonal injury in CN III, IV, or VI
  • Pupil-sparing CN III palsy = ischaemic/diabetic cause - damage is in the nerve core, sparing superficial parasympathetic fibres
  • Pupil-involved CN III palsy = compressive lesion (e.g. posterior communicating artery aneurysm) - external compression affects outermost parasympathetic fibres first

Pupil involvement in CN III palsy = posterior communicating artery aneurysm until proven otherwise - neurosurgical emergency requiring urgent MRI/MRA.

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