What's going on?

There is an interruption in the sympathetic nerve supply to the eye. A lesion may occur anywhere along the route of the sympathetic nerves; i.e., the hypothalamus, the cervical spine, the thorax including the upper portion of the lung (see pancoast tumour) and the neck. Note: Keep in mind carotid artery dissection as a rare but important cause of acute Horner's syndrome.

If I examine the patient what will I find?

A small pupil (miosis) on the affected side with a small ptosis, anhidrosis (lack of sweating on the side of the face) and apparent enophthalmos because of a lowered upper lid and an elevated lower lid.

What if I've diagnosed it?

Refer soon/urgently via letter.

What will the hospital do?

Search for the cause. There are several pharmacological tests available that use drops to find exactly which order neurones are affected, thus allowing better localisation of the lesion causing the condition. Now that imaging is easily accessible, scans of the entire sympathetic tract are recommended.

What do I need to do?

A thorough search should be made for a cause. The neck should be palpated and the nasopharynx thoroughly examined.

What to tell the patient

This will depend on the underlying aetiology.

Problems that may arise, and how to deal with them

Very rarely, acute onset of unilateral Horner's syndrome may indicate an ipsilateral carotid artery dissection.