Horner Syndrome

Overview

Horner syndrome is a group of signs caused by disruption of the sympathetic nerve pathway that travels from the brain, down through the chest, and up the side of the neck to the eye and face. This pathway controls the pupil, part of the eyelid, and sweating on the face. When it is interrupted anywhere along its long route, the result is a characteristic set of findings on one side of the face.

The classic triad is a drooping upper eyelid (ptosis), a constricted (small) pupil that does not enlarge normally in dim light, and decreased sweating on the affected side of the face. Horner syndrome itself is not dangerous, but it is important because it is a sign that something is affecting the nerve pathway. The underlying cause can range from harmless to serious, so the main goal is to find out what is responsible. Identifying the cause guides treatment.

Symptoms

The signs of Horner syndrome appear on one side of the face and may be subtle:

• A mildly drooping upper eyelid (ptosis)
• A small pupil that does not widen normally in dim light, so the difference between the two pupils is more obvious in low light
• The affected eye may appear slightly sunken
• Reduced or absent sweating on that side of the face
• Sometimes a slight elevation of the lower eyelid
• In children, a difference in eye color (the affected iris may be lighter) when the syndrome is present from a young age

Other symptoms depend on the underlying cause. For example, sudden Horner syndrome with severe neck or facial pain, or with other neurological symptoms, needs urgent evaluation because it can occasionally signal a serious problem.

Causes

Horner syndrome results from anything that interrupts the sympathetic nerve pathway along its course. Causes are often grouped by where along the pathway the problem lies:

• Central (brain and spinal cord): Stroke, tumors, or conditions affecting the brainstem or upper spinal cord.
• Within the chest and neck: Tumors at the top of the lung, injury or surgery in the neck or chest, and an enlarging blood vessel (aneurysm).
• Near the carotid artery: A tear in the wall of the carotid artery in the neck, which can also cause pain and is a stroke risk.
• Other and unknown: Injury, certain headaches, or no identifiable cause in some cases. In children, it may be present from birth or follow birth-related injury.

Risk Factors

• Conditions affecting the brainstem or spinal cord, such as stroke or tumors
• Lung tumors at the top of the chest
• Neck or chest injury or surgery
• Carotid artery tear (dissection) or aneurysm
• Certain severe headaches, such as cluster headache
• Birth-related injury in infants

Diagnosis

Diagnosis involves confirming the syndrome and then searching for its cause:

• Clinical exam: Examining the pupils in light and dark, eyelid position, and facial sweating; the pupil difference is typically greater in dim light.
• Eye drop testing: Special eye drops can confirm Horner syndrome and help localize where along the pathway the problem lies.
• Imaging: Depending on the suspected location and the person's symptoms, this may include MRI or CT of the brain, neck, and chest, and imaging of the blood vessels in the neck.
• Additional tests: Chosen based on the likely cause, such as evaluation for a carotid artery tear when there is associated pain.

Treatment

There is no treatment for Horner syndrome itself; care is directed at the underlying cause:

• Treating the cause: Management depends on what is found, such as treating a stroke, a carotid artery tear, an infection, or a tumor.
• Monitoring: When no serious cause is found or the cause resolves, the signs may improve on their own or remain stable and simply be observed.
• Symptom-related measures: The eyelid droop in Horner syndrome is usually mild and rarely affects vision; if cosmetic concerns are significant, options can be discussed with an eye specialist.

Because the same nerve pathway is involved in some serious conditions, the most important part of management is a careful evaluation to identify and treat any underlying problem promptly. Prognosis depends largely on that cause.

Prevention

Horner syndrome cannot be directly prevented because it is a sign of another condition, but you can reduce some underlying risks:

• Manage stroke risk factors such as blood pressure, diabetes, and smoking
• Avoid neck injuries and use seatbelts and protective gear
• Seek prompt care for severe or unusual neck pain or sudden facial changes
• Attend recommended health screenings

When to See a Doctor

See a doctor if you notice a persistent drooping eyelid, a difference in pupil size, or reduced sweating on one side of the face, since these warrant evaluation to find the cause. A new, unexplained difference in pupil size should always be checked.

Seek emergency care if these signs come on suddenly, especially with severe neck, face, or head pain, double vision, slurred speech, weakness, numbness, or dizziness. Sudden Horner syndrome can occasionally accompany a carotid artery tear or stroke, where prompt treatment is critical.

Related Topics

Frequently Asked Questions

References

1. National Institute of Neurological Disorders and Stroke (NINDS). Neurological disorders information.
2. Mayo Clinic. Horner syndrome — Symptoms and causes.
3. American Academy of Ophthalmology. Horner syndrome.
4. MedlinePlus, U.S. National Library of Medicine. Horner syndrome.