Horner Syndrome

The three classic signs

• Ptosis: the upper eyelid droops by 1 to 2 mm. The lower lid may sit slightly higher (upside-down ptosis), making the eye look smaller or sunken.
• Miosis: the pupil on the affected side is smaller. The difference is most obvious in dim light, because the affected pupil dilates slowly (dilation lag).
• Anhidrosis: less sweating on that side of the face. This depends on where the nerve damage is, and is often absent.

Other features:

• in Horner syndrome present from birth or early childhood, the iris on the affected side may be lighter in color (heterochromia)
• facial flushing on the opposite side in some cases

Vision is normal. The pupil still reacts to light.

How the nerve pathway works

The sympathetic nerves to the eye travel in three segments:

1. First-order neuron: from the hypothalamus down the brainstem and spinal cord to the upper chest level.
2. Second-order neuron: exits the spinal cord, passes over the top of the lung, and runs up the neck.
3. Third-order neuron: travels along the internal carotid artery into the skull and to the eye.

Where the damage is points to the cause.

Causes

In some people no cause is found.

Carotid artery dissection

A tear in the wall of the carotid artery is one of the most important causes in adults. It can follow neck trauma, chiropractic manipulation, coughing or sports, or occur spontaneously. Pain on one side of the neck, face or head together with new Horner signs is a medical emergency, because dissection can cause a stroke.

Pancoast tumor

A lung cancer at the top of the lung can invade the sympathetic chain and the nerves to the arm, causing shoulder and arm pain, hand weakness and Horner syndrome. It is more common in smokers.

Diagnosis

Confirming Horner syndrome

An eye doctor or neurologist measures the pupils in bright and dim light and may use eye drops:

• Apraclonidine drops: cause the affected pupil to enlarge and the lid to lift, reversing the size difference.
• Cocaine drops: the normal pupil dilates but the affected one dilates poorly.
• Hydroxyamphetamine drops: help separate third-order from earlier causes, though availability is limited.

Finding the cause

• MRI of the brain and neck, with MR angiography, or CT angiography of the head and neck to look for dissection, stroke and tumors.
• Chest imaging (CT) to check the top of the lungs.
• In children: imaging of the head, neck, chest and abdomen, and urine tests (catecholamines) to look for neuroblastoma.

The urgency and choice of tests depend on how suddenly it appeared and the other symptoms.

Treatment

There is no treatment for Horner syndrome itself. Treatment targets the cause:

• antiplatelet or anticoagulant medicines for carotid dissection
• stroke care
• surgery, chemotherapy or radiation for tumors
• management of cluster headache

The droopy eyelid is usually mild. If it bothers you, eye drops (such as apraclonidine or oxymetazoline) can lift it temporarily, and minor eyelid surgery is possible.

Outlook

The outlook depends on the cause. Horner signs may improve if the nerve recovers, for example after dissection heals, but often persist. They do not affect vision. The underlying cause is what determines long-term health.

Frequently asked questions

What are the symptoms of Horner syndrome?

The classic signs are a mildly drooping upper eyelid, a smaller pupil and reduced sweating on the same side of the face. The pupil difference is easiest to see in dim light. Vision is not affected, and many people only notice it in photos.

Is Horner syndrome serious?

The eye signs are harmless, but the cause can be serious. Sudden Horner syndrome with neck or head pain can mean a carotid artery tear, and other causes include stroke and lung tumors. Any new Horner syndrome should be evaluated promptly.

What causes Horner syndrome?

It is caused by damage to the sympathetic nerves to the eye anywhere along their path from the brain, down the spinal cord, over the top of the lung and up the neck. Common causes include carotid artery dissection, stroke, lung tumors, neck surgery or injury, and neuroblastoma in children.

Can Horner syndrome go away?

Sometimes. If the underlying cause, such as a carotid dissection, heals, the signs can improve over months. In many people they persist. Eye drops or minor eyelid surgery can improve a noticeable droop.