Extraocular motor nerve palsies
Extraocular motor nerve palsies are dysfunctions of the third, fourth, and sixth cranial nerves. 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 trauma, diabetes, or an intracranial aneurysm.
Causes and incidence
The most common extraocular motor nerve palsy affects the superior oblique muscle as a result of trauma. Other causes of these disorders vary, depending on the cranial nerve involved:
❑ Third nerve (oculomotor) palsy (acute ophthalmoplegia) may be congenital or acquired. Causes include oculomotor involvement resulting from intracranial tumors or aneurysms; diabetic neuropathy; and trauma.
❑ Sixth nerve (abducens) palsy commonly has an unknown etiology. Strokes are a common cause. Brain stem lesions, elevated intracranial pressure, inflamed petrous pyramid due to otitis media, cavernous sinus, orbital involvement with tumor and inflammation, or thyroid eye disease may be responsible for sixth nerve palsy.
There are approximately 4,500 cases of acquired extraocular motor nerve palsies in the United States. The incidence of congenital extraocular nerve palsies is unknown.
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 (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 displays diplopia and an inability to rotate the eye downward or upward. The head is tilted to the side opposite the involved area in superior oblique palsy.
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 and can develop torticollis.
Diagnosis
Diagnosis necessitates an orthoptic examination to isolate the involved muscle, a complete neuro-ophthalmologic examination, and a thorough patient history. Differential diagnosis of third, fourth, or sixth nerve palsy depends on the specific motor defect exhibited by the patient.
For all extraocular motor nerve palsies, a computed tomography scan or magnetic resonance imaging rules out tumors and may help detect the cause of the palsy, such as the cause of increased intracranial pressure. The patient is also evaluated for an aneurysm or diabetes. If sixth nerve palsy results from infection, culture and sensitivity tests identify the causative organism, and specific antibiotic therapy can be determined.
Treatment
Identification of the underlying cause is essential because treatment for extraocular motor nerve palsies varies accordingly. Neurosurgery is necessary if the cause is a brain tumor or an aneurysm. For infection, massive I.V. doses of antibiotics may be appropriate.
Special considerations
❑ If the palsy results from thyroid eye disease, the patient must have normal thyroid levels before eye muscle surgery is attempted.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
Other Book Chapters Related to Nerve symptoms
Read excerpts from these other book chapters related to Nerve symptoms:
Medical Books Excerpts
- Paresthesia
- "Professional Guide to Signs & Symptoms (Fifth Edition)" (2006)
- [ read ]
- Paresthesia
- "Signs & Symptoms: A 2-in-1 Reference for Nurses" (2007)
- [ read ]
Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2008 Williams & Wilkins.
More About Causes of Nerve symptoms
» Next page: Paresthesia (Professional Guide to Signs & Symptoms (Fifth Edition))
Rate This Website
What do you think about the features of this website?
Take our user survey and have your say:
Website User Survey
Medical Tools & Articles:
Next articles:
Tools & Services:
Medical Articles:
Forums & Message Boards
- Ask or answer a question at the Boards:
