Cranial Nerve Palsies (III, IV, VI)

Key points

• III nerve palsy: eye 'down and out' with ptosis ± pupil dilation; pupil-involved → posterior communicating artery aneurysm until proven otherwise; pupil-spared → microvascular (diabetes, hypertension).
• IV nerve palsy: vertical diplopia, head tilt away; common after trauma.
• VI nerve palsy: horizontal diplopia, failure of abduction — 'false localising sign' of raised ICP.
• Multiple cranial neuropathies: consider cavernous sinus pathology.

Decision points in this pathway

• Pupil involved (dilated)?

The full step-by-step algorithm, including what to do at each branch, opens in the app for approved members.