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Sixth Cranial Nerve (Abducens Nerve) Palsy

By Michael Rubin, MDCM, Professor of Clinical Neurology;Director, Neuromuscular Service and EMG Laboratory, Weill Cornell Medical College;New York Presbyterian Hospital-Cornell Medical Center

A palsy of the 6th cranial nerve affects the ability to turn the eye outward.

Palsy refers to paralysis, which can range from partial to complete.

Many disorders can cause this palsy:

Some of these disorders, such as tumors and brain abscesses, increase pressure within the skull and put pressure on (compress) the nerve. Other disorders, such as a blocked artery, interfere with blood flow to the nerve.

If 6th cranial nerve palsy occurs alone (without other cranial nerve palsies), its cause is often never identified.

Symptoms

The affected eye cannot turn fully outward and may turn inward when people look straight ahead. Double vision occurs when people look toward the side of the affected eye.

Other symptoms of 6th cranial nerve palsy depend on the cause. For example, disorders that increase pressure inside the skull may cause a severe headache and temporary blurring of vision when people move their head suddenly. Also, the face and mouth may be numb, and people may be unable to move the affected eye in other directions.

Diagnosis

  • Neurologic examination

  • Ophthalmoscopy

  • Computed tomography or magnetic resonance imaging

  • Sometimes a spinal tap

  • Sometimes blood tests

Usually, doctors can easily identify a 6th cranial nerve palsy, based on results of an eye examination. However, the cause is less obvious.

An ophthalmoscope (see Figure: What Is an Ophthalmoscope?) is used to look into the eye and check for evidence of increased pressure within the skull and abnormalities in blood vessels. Computed tomography (CT) or, preferably, magnetic resonance imaging (MRI) of the brain is done to exclude tumors and other abnormalities that may be increasing pressure within the skull. If results of imaging are normal, a spinal tap (lumbar puncture) may be done to determine whether an infection or bleeding is present.

If symptoms suggest vasculitis, blood is withdrawn to check for evidence of inflammation, such as certain abnormal antibodies (antinuclear antibodies and rheumatoid factor) and an abnormal erythrocyte sedimentation rate (ESR—how quickly red blood cells settle to the bottom of a test tube containing blood). After all tests are done, the cause may remain unknown.

Treatment

  • Treatment of the cause

Treatment of 6th cranial nerve palsy depends on the cause. When the cause is treated, the palsy usually resolves.

Palsies with no identifiable cause usually resolve without treatment within 2 months, as do those due to a blocked blood vessel.

* This is the Consumer Version. *