A 34-year-old woman develops acute neck pain followed by left-sided hemiparesis. Examination shows ptosis and miosis of the right eye with anhidrosis, while the pupil reacts normally to light. Carotid bruit is heard on the right. MRI shows an infarct in the right middle cerebral artery territory. The most likely diagnosis is:

• A Right internal carotid artery dissection ✓
• B Right third nerve palsy with embolic stroke
• C Right lateral medullary infarct
• D Temporal arteritis with right ophthalmic artery involvement

Explanation

Painful Horner syndrome (partial ptosis, miosis, anhidrosis) combined with ipsilateral cerebral ischaemia and neck pain is the classic presentation of internal carotid artery dissection, caused by stretch or compression of sympathetic fibres around the vessel. Third nerve palsy causes mydriasis with extraocular muscle weakness, not miosis. Lateral medullary infarct would add brainstem signs such as dysphagia and crossed sensory loss, which are absent.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.