Extraocular motor nerve palsies
Dysfunctions of the third, fourth, and sixth cranial nerves are called extraocular motor nerve palsies. Each of these nerves innervates specific muscles.
❑ The oculomotor (third cranial) nerve innervates the inferior, medial, and superior rectus muscles; the inferior oblique extraocular muscles; the pupilloconstrictor muscles; and the levator palpebrae muscles.
❑ The trochlear (fourth cranial) nerve innervates the superior oblique muscles.
❑ The abducens (sixth cranial) nerve innervates the lateral rectus muscles.
The superior oblique muscles control downward rotation, intorsion, and abduction of the eye. Complete dysfunction of the third cranial nerve is called total oculomotor ophthalmoplegia and may be associated with other central nervous system abnormalities. Myasthenia and dysthyroid disease should be examined as differential diagnoses.
Causes
The most common causes of extraocular motor nerve palsies are diabetic neuropathy and pressure from an aneurysm or brain tumor. Other causes of these disorders vary, depending on the cranial nerve involved.
❑ Third-nerve (oculomotor) palsy (acute ophthalmoplegia) may be congenital or acquired and causes diplopia. It may result from an aneurysm (particularly in the posterior communicating artery); microvascular disease, such as diabetes or hypertension; tumor; or trauma. Rare causes include uncal herniation, cavernous sinus mass lesion, orbital disease, herpes zoster, and leukemia. In children, a cause may be ophthalmic migraine.
❑ Fourth-nerve (trochlear) palsy also results from closed head trauma (blowout fracture) or sinus surgery.
❑ Sixth-nerve (abducens) palsy more commonly results from increased intracranial pressure; vasculopathic entities, such as diabetes, hypertension, and atherosclerosis; trauma; and idiopathic thyroid disease. Less common causes include giant cell arteritis, cavernous sinus mass (meningiomas, aneurysms, or metastasis), multiple sclerosis, and stroke.
Signs and symptoms
The most characteristic clinical effect of extraocular motor nerve palsies is diplopia of recent onset, which varies in different visual fields, depending on the muscles affected.
❑ Typically, the patient with third-nerve palsy exhibits ptosis, exotropia (in which the eye looks outward), pupil dilation, and unresponsiveness to light; the eye is unable to move and can’t accommodate.
❑ The patient with fourth-nerve palsy complains of diplopia and displays an inability to rotate the eye downward or upward. The patient develops a head tilt to compensate for vertical diplopia.
❑ Sixth-nerve palsy causes one eye to turn; the eye can’t abduct beyond the midline. To compensate for diplopia, the patient turns his head to the unaffected side.
Diagnosis
A complete neuro-ophthalmologic examination and thorough patient history are needed to diagnose these palsies. Differential diagnosis of third-, fourth-, or sixth-nerve palsy depends on the specific motor deficit exhibited by the patient.
For all extraocular motor nerve palsies, magnetic resonance imaging and computed tomographic scans rule out tumors and aneurysms. The patient is also evaluated for diabetes, and an erythrocyte sedimentation rate may be obtained to rule out giant cell arteritis.
Treatment
Identification of the underlying cause is essential because treatment of extraocular motor nerve palsies varies accordingly. Neurosurgery is necessary if the cause is an intracranial tumor or an aneurysm. For giant cell arteritis, high-dose corticosteroids are given I.V.; this is called pulse therapy.
Special considerations
❑ After treatment of the primary condition, the patient may need surgery to realign the extraocular muscles.
Book Source Details
- Book Title: Handbook of Diseases
- Author(s): Springhouse
- Year of Publication: 2003
- Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.
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Copyright Details: Handbook of Diseases, Copyright © 2008 Williams & Wilkins.
More About Causes of Nerve symptoms
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More About This Book:
Title: Handbook of Diseases
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2003
ISBN: 1-58255-266-5
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