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Sixth Cranial (Abducens) Nerve Palsy

By

Michael Rubin

, MDCM, Weill Cornell Medical College

Last full review/revision Jun 2019| Content last modified Jun 2019
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Sixth cranial nerve palsy affects the lateral rectus muscle, impairing eye abduction. The eye may be slightly adducted when the patient looks straight ahead. The palsy may be secondary to nerve infarction, Wernicke encephalopathy, trauma, infection, or increased intracranial pressure, or it may be idiopathic. Determining the cause requires MRI and often lumbar puncture and evaluation for vasculitis.

Etiology

Sixth cranial (abducens) nerve palsy results from the following:

Children with respiratory infection may have recurrent palsy. However, the cause of an isolated 6th cranial nerve palsy is often not identified.

Symptoms and Signs

Symptoms of 6th cranial nerve palsy include binocular horizontal diplopia when looking to the side of the paretic eye. Because the tonic action of the medial rectus muscle is unopposed, the eye is slightly adducted when the patient looks straight ahead. The eye abducts sluggishly, and even when abduction is maximal, the lateral sclera is exposed. With complete paralysis, the eye cannot abduct past midline.

Palsy resulting from a cavernous sinus lesion (eg, due to thrombosis, infection, tumor, or an aneurysm) can cause severe head pain, chemosis (conjunctival edema), anesthesia in the distribution of the 1st and 2nd division of the 5th cranial nerve, and paralysis of the 3rd, 4th, and 6th cranial nerves. Both sides may be affected, although unevenly.

Diagnosis

  • MRI

  • If vasculitis is suspected, erythrocyte sedimentation rate (ESR), antinuclear antibodies, and rheumatoid factor

A 6th nerve palsy is usually obvious, but the cause is not. If retinal venous pulsations are seen during ophthalmoscopy, increased intracranial pressure is unlikely.

CT is often done because it is often immediately available. However, MRI is the test of choice; MRI provides greater resolution of the orbits, cavernous sinus, posterior fossa, and cranial nerves. If imaging results are normal but meningitis or benign intracranial hypertension is suspected, lumbar puncture is done.

If vasculitis is suspected clinically, evaluation begins with measurement of ESR, antinuclear antibodies, and rheumatoid factor.

In children, if increased intracranial pressure is excluded, respiratory infection is considered.

Treatment

  • Treatment of the cause

In many patients, 6th cranial nerve palsies resolve once the underlying disorder is treated. Idiopathic palsy and ischemic palsy usually abate within 2 months.

Key Points

  • Sixth cranial (abducens) nerve palsy typically results from small-vessel disease, particularly in diabetics, but the cause is often unidentified.

  • This palsy may cause impaired abduction and horizontal diplopia.

  • To identify the cause, do neuroimaging (preferably MRI), followed by lumbar puncture if imaging results are normal and benign intracranial hypertension is suspected; if vasculitis is suspected, start with erythrocyte sedimentation rate (ESR), antinuclear antibodies, and rheumatoid factor.

  • If increased intracranial pressure is excluded in children, consider respiratory infection.

  • Sixth cranial nerve palsy usually resolves whether a cause is identified or not.

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NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
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