You are in: eMedicine Specialties > Ophthalmology > EXTRAOCULAR MUSCLES Abducens Nerve PalsyArticle Last Updated: Jul 14, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 9
  Author: Michael P Ehrenhaus, MD, Director, Department of Cornea, External Disease & Refractive Surgery, Assistant Professor, Department of Ophthalmology, State University of New York Downstate Medical Center Michael P Ehrenhaus is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, American Medical Association, American Society of Cataract and Refractive Surgery, and Contact Lens Association of Ophthalmologists Coauthor(s): Mohammedyusuf E Hajee, MD, Clinical Assistant Instructor, Staff Physician, Department of Ophthalmology, Director, Blood Flow Laboratory, State University of New York-Downstate Medical Center; Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences Editors: Andrew W Lawton, MD, Medical Director of Neuro-Ophthalmology Service, Section of Ophthalmology, Baptist Eye Center, Baptist Health Medical Center; Simon K Law, MD, PharmD, Assistant Professor of Ophthalmology, Jules Stein Eye Institute; Chief of Section of Ophthalmology Surgical Services, Department of Veterans Affairs Healthcare Center, West Los Angeles; Brian R Younge, MD, Professor of Ophthalmology, Mayo Clinic School of Medicine; Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri; James P Gills, MD, Founder, St Luke's Cataract and Laser Institute; Professor, Department of Ophthalmology, University of South Florida College of Medicine Author and Editor Disclosure Synonyms and related keywords: sixth nerve palsy, VI nerve palsy, 6th nerve palsy, cranial nerve VI palsy INTRODUCTIONSection 2 of 9
  BackgroundCranial nerve VI, also known as the abducens nerve, innervates the ipsilateral lateral rectus (LR), which functions to abduct the ipsilateral eye. It has the longest subarachnoid course of all the cranial nerves; therefore, its syndromes are similar to those of the fourth nerve because of their long intracranial courses. The sixth nerve nucleus is located in the pons, just ventral to the floor of the fourth ventricle and just lateral to the medial longitudinal fasciculus (MLF). About 40% of its neurons protect into the ipsilateral MLF only to cross over to the contralateral side and ascend to innervate that contralateral medial rectus subnucleus to participate in contralateral eye adduction. Patients usually present with binocular horizontal diplopia (double vision producing a side-by-side image with both eyes open) and esotropia in primary gaze. The deviation, as would be expected, is noted to be greater when the patient fixates with the paretic eye at distance. Patients also may present with a head-turn to maintain binocularity and binocular fusion and to minimize diplopia. It is rare to find true congenital sixth nerve palsy. A typical workup of a sixth nerve palsy involves excluding paresis of other cranial nerves (including VII and VIII), a check of ocular muscle motility and evaluating pupillary responsiveness. Checking deep tendon reflexes (DTRs) and motor function to exclude corticospinal tract involvement also is important. MRI is indicated for any brainstem findings to exclude pontine glioma in children (most have papilledema and nystagmus without other cranial nerve involvement) and in adults that show no improvement. In young adults, a lumbar puncture (LP) for cerebrospinal fluid (CSF) analysis is completed to exclude meningitis in patients who have no history of diabetes or hypertension and who have a negative head CT scan. Senior patients should have blood testing for an erythrocyte sedimentation rate (ESR) and/or a C-reactive protein to screen for giant cell (temporal, cranial) arteritis. Poor or no resolution should prompt a full neurologic evaluation and a consideration of other possible diagnoses (eg, congenital esotropia, Möbius syndrome, Duane syndrome). PathophysiologyOnly the ipsilateral lateral rectus that is solely innervated by the involved peripheral sixth cranial nerve is affected; therefore, only deviations in the horizontal plane are produced. In isolated cases of peripheral nerve lesions, no vertical or torsional deviations are present. Central nervous system lesions of the abducens nerve tract are localized easily secondary to the typical findings associated with each kind of lesion. Damage to the sixth nerve nucleus results in an ipsilateral gaze palsy. The lack of a contralateral adduction defects makes it easy to differentiate nuclear from a fascicular or nonnuclear lesion. Abducens palsy frequently is seen as a postviral syndrome in younger patients and as an ischemic mononeuropathy in the adult population. FrequencyUnited StatesSixth nerve palsies fall into the following categories: 8-30% idiopathic, 10-30% miscellaneous, 3-30% trauma, 0-6% aneurysm, and 0-36% ischemic. The sixth cranial nerve is the most commonly affected of the ocular motor nerves. In children, it is second most common after the fourth nerve, with an incidence of 2.5 cases per 100,000 in the population. Mortality/MorbidityA young patient should have an aggressive workup because of the greater likelihood of a neoplasm causing the palsy. Patients older than 40 years require a less aggressive workup because of the greater likelihood of the etiology being more benign in nature (eg, ischemic mononeuropathy, vasculopathy). AgeCranial nerve VI palsy can occur in all age groups; however, the etiology varies depending on the age group. CLINICALSection 3 of 9
HistoryClinical history includes the following:
PhysicalPhysical findings include the following:
CausesNot all abduction deficits are cranial nerve VI palsies. Mimickers are orbital lesions, medial wall fractures, Duane syndrome, thyroid disease, and myasthenia gravis.
DIFFERENTIALSSection 4 of 9
Giant Cell Arteritis
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