Horner syndrome: What causes it?

Horner syndrome is a rare disorder caused by damage to the sympathetic nerves of the face and eye. The sympathetic nerves control circulation and perspiration.

Horner syndrome isn't a disease but a sign of an underlying — often serious — disorder. Causes of Horner syndrome include:

• Brainstem stroke
• Tumor in the upper part of the lung and low cervical spinal cord
• Cluster headaches
• Injury to the carotid artery in the neck

Signs and symptoms of Horner syndrome occur on the side of the face on which the sympathetic nerve has been damaged and include:

• Drooping of the upper eyelid (ptosis) and slight elevation of the lower lid
• Decreased pupil size in the affected eye
• Decreased or absent sweating on the affected side of the face (anhidrosis)

The physical signs of Horner syndrome are so subtle that they often go undetected. An ophthalmologist may confirm a diagnosis by special eye tests. There's no specific treatment for Horner syndrome. Treatment is directed at the underlying cause when possible.