Abducens nerve palsy
Abducens Nerve Palsy: Description, Causes and Risk Factors:
Alternative Name: Sixth nerve palsy, lateral rectus palsy, cranial mononeuropathy VI.
Cranial nerve six supplies the lateral rectus muscle allowing for outward (abduction) eye movement. A sixth nerve palsy, also known as abducens nerve palsy, is a neurological defect resulting from an impaired sixth nerve or the nucleus that controls it. This may result in horizontal double vision (diplopia) with in turning of the eye and decreased lateral movement. Abducens nerve palsy is the most commonly affected of the ocular motor nerves. In children, it is the second most common after the fourth nerve, with an incidence of 2.5 cases per 100,000 in the population
In general terms, the most common causes of abducens nerve palsy in adults are:
More common causes may include diabetes, hypertension, atherosclerosis, trauma, idiopathic.
- Less common causes may include increased intracranial pressure, giant cell arteritis, cavernous sinus mass (e.g. meningioma, brainstem glioblastoma aneurysm, metastasis), multiple sclerosis, sarcoidosis/vasculitis, post-myelography or lumbar puncture, stroke (usually not isolated).
The affected individual will have an esotropia or convergent squint on distance fixation. On near fixation the affected individual may have only a latent deviation and be able to maintain binocularity or have an esotropia of a smaller size. Patients sometimes adopt a face turn towards the side of the affected eye, moving the eye away from the field of action of the affected lateral rectus muscle, with the aim of controlling diplopia and maintaining binocular vision.
Diplopia is typically experienced by adults with abducens nerve palsy, but children with the condition may not experience diplopia due to suppression. The neural plasticity present in childhood allows the child to 'switch off' the information coming from one eye, thus relieving any diplopic symptoms. Whilst this is a positive adaptation in the short term, in the long term it can lead to a lack of appropriate development of the visual cortex giving rise to permanent visual loss in the suppressed eye; a
condition known as amblyopia.
The most common symptom is binocular horizontal diplopia. This manifests when you look to the side of the paretic eye. When the patient looks straight ahead, his/her eye becomes slightly adducted. The affected eye abducts abnormally. The lateral sclera is fully exposed when abduction is maximal.
Other symptoms may include:
Diagnosis is usually based on laboratory data and imaging. These may include:
Laboratory studies may include:
CBC (complete blood cell) count.
- Glucose levels.
- Glycosylated hemoglobin (HbA1C).
- Erythrocyte sedimentation rate (ESR) and/or C-reactive protein
- Rapid plasma reagin test.
- Fluorescent treponemal antibody-absorption test.
- Lyme titer.
- Glucose tolerance test.
- Antinuclear antibody test.
- Rheumatoid factor.
- Antinuclear antibodies.
Imaging Studies: MRI or CT scan.
The first aims of management should be to identify and treat the cause of the condition, where this is possible, and to relieve the patient symptoms, where present. In children, who rarely appreciate diplopia, the aim will be to maintain binocular vision and, thus, promote proper visual development. In adults initial treatment may include Fresnel prisms, occlusion, or even BOTOX injections.
Thereafter, a period of observation of around 9 to 12 months is appropriate before any surgical intervention, as some palsies will recover without the need for surgery.
The procedure chosen will depend upon the degree to which any function remains in the affected lateral rectus. Where there is complete paralysis, the preferred option is to perform vertical muscle transposition procedures. An alternative, and less satisfactory, approach is to operate on both the lateral and medial rectii of the affected eye, with the aim of stabilizing it at the midline, thus giving single vision straight ahead but diplopia on both left and right gaze. This procedure is rarely used, but might be appropriate for those with total paralysis who, because of other health problems, are at increased risk of the anterior segment ischemia associated with complex multi-muscle transposition procedures.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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