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 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.
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.
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.
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. The patient is also evaluated for diabetes, and an erythrocyte sedimentation rate may be obtained to rule out giant cell arteritis .
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, highdose corticosteroids are given I.V.; this is called pulse therapy.
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