Cranial Nerve Disorders

Published on 14/05/2017 by admin

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Last modified 14/05/2017

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E. Lee Murray, MD

OVERVIEW

The most common primary cranial nerve deficits to come to the attention of the hospital neurologist are listed below. Not discussed here are other medical disorders which produce cranial nerve deficits as part of their clinical presentation including vascular disease (Chapter 16), demyelinating disease (Chapter 22), infectious diseases (Chapter 17) and tumors (Chapter 25). The disorders with primary cranial nerve manifestations include:

Bell palsy

Ramsay-Hunt syndrome

Hemifacial spasm (Chapter 23)

Herpes zoster ophthalmicus

Vestibulopathies (Chapter 32)

Trigeminal neuralgia (Chapter 20)

Glossopharyngeal neuralgia

Multiple cranial nerve palsies

Some of these are discussed in the chapters indicated. The remainder are discussed in this chapter.

BELL PALSY AND RAMSAY-HUNT SYNDROME

Bell palsy is the most common cause of unilateral facial weakness. The most common causes are herpes simplex virus (HSV) and varicella zoster virus (VZV); less likely are autoimmune and other infections. Ramsay-Hunt syndrome is peripheral facial palsy with herpes zoster oticus.

PRESENTATION is with subacute onset of unilateral facial palsy, typically involving upper and lower face (peripheral palsy), although early in the course or with milder symptoms the upper face involvement may be difficult to determine and the lesion might be thought to be central. Pain in or around the ipsilateral ear may be present before, contemporaneous with, or after the onset of the weakness. Bilateral involvement is uncommon and when present suggests diagnoses other than idiopathic facial palsy.

DIAGNOSIS is considered in all patients with unilateral facial weakness. Classic clinical features can make the diagnosis with sufficient accuracy to avoid extensive evaluation. With atypical presentation or other associated symptoms, additional study may be needed. The main differential diagnoses are stroke and demyelinating disease, although diabetes, cerebellopontine angle (CPA) tumor, Lyme disease, and infectious or neoplastic meningitis are considered. Magnetic resonance imaging (MRI) of the brain with special attention to the facial nerve can show inflammatory change but is of most value in ruling out other lesion such as tumor, stroke, or demyelinating plaque.

MANAGEMENT includes protection of the eye from exposure if eye closure and blinking are incomplete. Corticosteroids and antiviral agents are considered.1

Corticosteroids can hasten recovery and reduce residual damage. These are usually used unless contraindicated by comorbid condition (e.g., uncontrolled diabetes).

Antivirals have been used but their benefit is unproved. They may be considered especially for patients with severe deficit.

DIABETIC OPHTHALMOPLEGIA

Diabetic ophthalmoplegia is a common cause for hospital neurology consultation because of concerns over stroke syndrome or aneurysm. Etiology is likely ischemia affecting the central portion of the nerve, sparing the peripheral fibers innervating the pupil.

PRESENTATION is most commonly with pupil-sparing CN 3 palsy producing diplopia but without anisocoria unless there is another reason for that. Ptosis can occur. Pain can occur in a peri-orbital distribution. CN 6 or 4 palsies can occur but with lower incidence.

DIAGNOSIS is suspected in a diabetic with pupil-sparing CN 3 palsy. However, imaging with MRI and MR angiography (MRA) is almost always needed to look for aneurysm, cavernous sinus lesion, or other lesion. Brainstem ischemia or demyelination would be unlikely to produce an isolated cranial nerve palsy.

MANAGEMENT is supportive. The key is to rule out more concerning lesions. Most patients improve.

ABDUCENS NERVE PALSY

Abducens palsy in adults is usually due to ischemic neuropathy. Typical vascular risk factors predispose to this.

PRESENTATION is with horizontal diplopia, worse with lateral gaze to the affected side. With complete lesions, the eye does not abduct beyond the midline. If the abducens palsy is vascular, no other deficit is expected. If the lesion is in the cavernous sinus, CSF, or elsewhere in the brain, then additional deficits would be expected.

DIAGNOSIS is suspected by horizontal diplopia in the absence of other findings.

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