Cranial Nerve Palsy

What the cranial nerves do

There are 12 pairs of cranial nerves. Each one is numbered with a Roman numeral and controls specific functions. A palsy means the nerve is not working properly, causing weakness, loss of movement or loss of sensation.

The nerves for smell (I) and vision (II) are technically cranial nerves too, but their problems are usually described as smell loss or optic neuropathy rather than palsy.

Symptoms of cranial nerve palsy

Eye movement palsies (III, IV and VI)

These are the palsies most people mean by the term. The main symptom is double vision that goes away when you cover one eye. Other clues:

• Third nerve palsy: a drooping eyelid that may completely close the eye, the eye pointing down and out, and in some cases a dilated pupil that does not react to light. A third nerve palsy with a big pupil is an emergency until an aneurysm is ruled out.
• Fourth nerve palsy: one image above or tilted relative to the other. People often tilt their head away from the affected side to compensate. Old childhood photos sometimes show the same head tilt, which suggests a long-standing congenital palsy that has started to cause symptoms.
• Sixth nerve palsy: side-by-side double vision that is worse looking toward the affected side and at distance. In children and adults it can be a sign of raised pressure inside the skull.

Facial nerve palsy (VII)

One side of the face droops, the forehead cannot wrinkle, the eye cannot close fully, and the mouth droops. Taste on the front of the tongue may change and sounds may seem loud. Bell's palsy is the most common cause. A stroke usually spares the forehead, while a facial nerve palsy affects the whole side of the face.

Lower cranial nerve palsies (IX to XII)

These cause hoarse voice, choking or coughing when swallowing, nasal-sounding speech, shoulder weakness, or a tongue that wastes or points to one side. They often occur together and suggest a problem at the base of the skull or in the brainstem.

Causes

Microvascular (small vessel) disease

In adults over 50, especially with diabetes, high blood pressure or high cholesterol, the most common cause of an isolated III, IV or VI palsy is reduced blood flow to the nerve. These palsies often start with pain around the eye, usually spare the pupil, and recover on their own.

Inflammation and infection

• Viral inflammation, especially with herpes simplex or varicella zoster (Ramsay Hunt syndrome)
• Lyme disease, which can cause facial palsy on one or both sides
• Meningitis, sinus infections spreading to the skull base, and middle ear infections
• Multiple sclerosis, sarcoidosis and Guillain-Barré syndrome (Miller Fisher variant)

Compression and structural causes

• Brain aneurysm, particularly of the posterior communicating artery pressing on the third nerve
• Brain tumors, acoustic neuroma, pituitary tumors and skull base tumors
• Raised intracranial pressure from hydrocephalus, bleeding or idiopathic intracranial hypertension
• Cavernous sinus thrombosis or carotid-cavernous fistula

Other causes

• Head injury: the fourth nerve is particularly vulnerable.
• Stroke affecting the brainstem.
• Giant cell arteritis in people over 50, which can also threaten vision.
• Congenital palsies present from birth.

Conditions such as myasthenia gravis and thyroid eye disease can mimic a cranial nerve palsy by affecting the muscle or the junction between nerve and muscle.

How a cranial nerve palsy is diagnosed

A doctor, often a neurologist or neuro-ophthalmologist, will:

1. Test eye movements in every direction, eyelid position and pupil reactions.
2. Test facial strength, facial sensation, hearing, swallowing, tongue and shoulder movements to see how many nerves are involved.
3. Check the optic nerves at the back of the eye for swelling, a sign of raised pressure.

Tests depend on the pattern:

• MRI of the brain with contrast, and often MR or CT angiography to look for an aneurysm
• Blood tests: blood sugar and HbA1c, ESR and CRP (for giant cell arteritis), and sometimes Lyme or myasthenia antibodies
• Lumbar puncture if infection, inflammation or abnormal pressure is suspected

Imaging may be delayed in an older adult with diabetes and a classic pupil-sparing palsy, but it is done if recovery does not start in about 3 months or if other symptoms appear.

Treatment

Treatment targets the cause:

• Microvascular palsy: control of blood sugar, blood pressure and cholesterol. The nerve usually recovers on its own.
• Bell's palsy: oral steroids started within 72 hours improve recovery. Antivirals are sometimes added in severe cases.
• Aneurysm or tumor: neurosurgery, endovascular coiling, radiation or other cancer treatment.
• Infection: antibiotics or antivirals.
• Giant cell arteritis: high-dose steroids started immediately.

Managing symptoms while the nerve recovers

• Double vision: an eye patch or frosted tape on one lens of your glasses. Prisms can be fitted to lenses. Alternate the patched eye in children to prevent amblyopia.
• Eye that will not close: lubricating drops by day, ointment and taping the lid at night to protect the cornea.
• Swallowing problems: a speech and language therapist can teach safe swallowing techniques.
• Persistent deviation: if no further recovery occurs after 6 to 12 months, eye muscle surgery or Botox can realign the eyes.

Do not drive while you have double vision unless your doctor says it is safe with a patch.

Outlook

Most microvascular third, fourth and sixth nerve palsies improve within 3 to 6 months. About 70 to 85% of people with Bell's palsy recover fully, most within 3 months. Palsies from trauma, tumors or aneurysms recover more slowly and less completely, depending on how badly the nerve was damaged and how quickly the cause was treated.

Frequently asked questions

What are the symptoms of cranial nerve palsy?

Symptoms depend on the nerve. Eye nerve palsies cause double vision, a drooping eyelid or an eye that turns in or out. A facial nerve palsy causes a drooping face and trouble closing the eye. Lower cranial nerve palsies cause hoarseness, swallowing problems or tongue weakness.

Is cranial nerve palsy serious?

It can be. Many palsies are caused by diabetes-related blood flow problems or viral inflammation and recover on their own. But a palsy can also be the first sign of an aneurysm, stroke, tumor or infection, so every new palsy needs prompt assessment, and some need emergency imaging.

Can a cranial nerve palsy go away on its own?

Yes, often. Palsies caused by small vessel disease from diabetes or high blood pressure usually improve within 3 to 6 months. Most Bell's palsy recovers within weeks to months. Palsies from structural causes need treatment of the cause.

Which cranial nerve palsy is most common?

Facial nerve palsy, usually Bell's palsy, is the most common overall. Among the eye movement nerves, sixth nerve palsy is the most common in adults, followed by fourth and third nerve palsies.

Can stress cause cranial nerve palsy?

Stress does not directly damage cranial nerves. It may play a role in reactivating viruses like herpes simplex that are linked to Bell's palsy. A new palsy should never be put down to stress without a medical examination.