PSSNEWS An On-Line Publication for COPE Continuing Education in Optometry Abducens Nerve Palsies 2.0 Hours - COPE 69959- NO This program is supported by an educational grant from Alcon Leonid Skorin Jr, OD, DO, FAAO, FAOCO Learning Objectives: 1. To correlate the anatomical course of the abducens cranial nerves with a patient's clinical presentation 2. To differentiate between abducens nerve palsies and their imposters 3. To determine an appropriate treatment regimen for a patient with an isolated abducens nerve palsy arteritis was made. The patient’s blood Case Presentation pressure was measured in the office and found An 83-year-old female presents with a recent to be normal. Blood work testing found a onset horizontal diplopia. She also complains normal fasting blood sugar but the patient’s of occipital headaches, fatigue and one recent complete blood count was positive for episode of amaurosis fugax. The patient normochromic, normocytic anemia. Her denied being a diabetic and she felt her Westergren erythrocyte sedimentation rate hypertension was adequately controlled with was grossly elevated at 120mm/hr and her C- atenolol. She does take one 81 mg. aspirin reactive protein value was also elevated. daily and has been recently taking The final diagnosis was temporal arteritis acetaminophen for her occipital headaches which was confirmed by temporal artery without relief. biopsy. The patient was started on high dose Examination confirmed a left abducens cranial oral prednisone and showed a significant nerve palsy. There was no afferent pupillary improvement in all her signs and symptoms. defect, visual acuity was 20/25 best corrected in each eye (the patient had mild-moderate Discussion of Case Presentation nuclear sclerotic cataracts), there was no This case highlights the importance of not papilledema and no other neurologic findings only localizing the abducens cranial nerve were present. palsy but incorporating this finding within the context of the patient’s other neurologic signs Based on the patient’s history and examination and symptoms. Although this patient had findings a tentative diagnosis of either definite risk factors for vasculopathic disease vasculopathic mononeuropathy or temporal (advanced age and hypertension) it was 1 actually her other neurologic (occipital fibers loop around the abducens nuclei. The headaches, amaurosis fugax) and abducens fascicle travels anteriorly through constitutional (fatigue) symptoms in the pons, lateral to the parapontine reticular combination with the recent onset diplopia formation, and through the pyramidal tract to that helped point to another possible vision exit the brain stem into the subarachnoid threatening diagnosis: temporal arteritis. spaces within the cerebellopontine angle.3 It then travels up the clivus over the petrous Further evaluation helped confirm this ridge where the nerve fibers are anchored at condition: the base of the skull to the tips of the petrous pyramids by the petrosphenoidal ligaments. Blood pressure measurement The nerve fibers enter the substance of the confirmed that the patient’s cavernous sinus and lie laterally, adjacent to hypertension was medically the carotid arteries. The nerve fibers enter the controlled. orbit through the medial portion of the superior orbital fissure where they innervate Diabetes was ruled-out with a fasting the lateral rectus muscle which moves the eye blood sugar. laterally.4 Anemia was identified with a complete The patient’s clinical presentation is a direct blood count. Low-grade anemia is a result of the location of the lesion along the common finding in patients with long and complicated course of the abducens temporal arteritis and helps explain nerve. Any associated neurologic signs or the patient’s complaint of fatigue. symptoms are a direct consequence of the local neuroanatomy. The erythrocyte sedimentation rate and the serum C-reactive protein were CONGENITAL ABDUCENS NERVE elevated. There is a combined PALSIES sensitivity of diagnosing temporal arteritis of 97% when both these tests MOBIUS SYNDROME (CONGENITAL are elevated. BULBAR PARALYSIS) Mobius syndrome is the occurrence of congenital bilateral sixth nerve and facial ANATOMY nerve deficits because the nerves, nuclei or both do not develop.5 The following are The paired sixth (abducens) cranial nerve common clinical findings: patients have a nuclei are located in the brainstem at the level mask-like facies, the mouth is often held open, of the pons, in the caudal portion of the atrophy of the tongue indicates hypoglossal paramedian pontine tegmentum, beneath the 1 cranial nerve involvement, the eyelids cannot floor of the fourth ventricle. Each nucleus be closed completely, deafness and mental contains two types of neurons: large motor retardation may occur, and there is complete cells whose axons form the ipsilateral sixth loss of horizontal eye movement but vertical cranial fascicle and nerve, and a group of eye movements are usually normal.5,6 Up to smaller cells, the internuclear neurons. The 40% of these children have an esotropia that is internuclear neurons send their axons across usually 50 prism diopters or greater.7 the midline to travel in the contralateral medial longitudinal fasciculus (MLF), where DUANE’S RETRACTION SYNDROME they synapse in the contralateral medial rectus subnucleus to coordinate conjugate horizontal There are three types of Duane’s retraction gaze.2 The seventh (facial) cranial nerve syndromes. Type I is the form that can be 2 confused with congenital esotropia or an damage the abducens nucleus produce a abducens nerve palsy. This disorder of ocular conjugate gaze palsy to the ipsilateral side. motility is characterized by limitation of Involvement of the adjacent paramedian abduction, narrowing of the palpebral fissure pontine reticular formation and medial and retraction of the globe on adduction, slight longitudinal fasciculus can produce the one- or no limitation of adduction and upshoot or and-a-half syndrome which consists of a downshoot on adduction.8 There is a female horizontal gaze palsy combined with an preponderance and a predilection for the left internuclear ophthalmoplegia.6 eye. The exact etiology for this syndrome is not known. Numerous theories including Lesions that involve the abducens nerve mechanical, innervational and central nervous fascicles produce an ipsilateral abducens nerve system anomalies have all been implicated. palsy and also affect adjacent pontine structures. Lesions in the pontine tegmentum ABDUCTION DEFECTS NOT DUE TO may produce an ipsilateral facial palsy, ABDUCENS PALSY Horner’s syndrome, facial anesthesia and peripheral deafness. This syndrome of the Not all abduction deficits are actual sixth dorsal pons is known as Foville’s syndrome. nerve palsies. Various orbital conditions such Ventral pontine lesions involving the as muscle entrapment secondary to trauma or abducens fascicles also involve the sinus surgery or dysthyroid ophthalmopathy corticospinal tracts and facial nerve fascicles. which causes a restriction of the medial rectus Such lesions produce an ipsilateral abducens muscle can cause an abduction deficit. Forced palsy with contralateral hemiparesis. If there duction testing would identify a restricted is an accompanying ipsilateral facial cranial muscle when the globe is rotated manually in nerve palsy this is known as Millard-Gubler the direction of the limited duction. syndrome and if there is no facial nerve palsy, it is known as Raymond-Cestan syndrome.6 Other causes of abduction deficits include inflammatory orbital pseudotumor (myositis) Within the subarachnoid space, the abducens and ocular myasthenia gravis. The Tensilon nerve travels a long intracranial course. (intravenous edrophonium) test would show Although it was thought that this extensive temporary resolution of the abduction deficit length made the nerve more vulnerable to indicating myasthenia as the underlying cause. numerous insults, it is actually the location and course, rather than its length, that are the Spasm of the near reflex can simulate bilateral major factors that lead to an abducens nerve sixth nerve palsies. Pupillary miosis, which is paresis.6 In this location the nerve lies in close part of the near triad along with convergence proximity or is actually bound to various and accommodation helps confirm the blood vessels. These include the anterior diagnosis. Occluding one of the patent’s eyes inferior cerebellar artery, posterior inferior will often resolve the abduction deficit 4 cerebellar artery and the basilar artery. Any of including the miosis and pseudomyopia. these blood vessels can cause compression of the nerve as they become atherosclerotic or It should be remembered that a break in fusion from aneurysmal formation.9 of a congenital esophoria can mimic an abduction paresis. Elevated intracranial pressure may result in downward displacement of the brainstem, with ACQUIRED ABDUCENS NERVE PALSIES stretching of the abducens nerve, which is Abducens nerve palsies often present with tethered at its exit from the pons and in other neurologic or neuro-ophthalmic findings Dorello’s canal found at the tip of the that help localize the lesion. Lesions that temporal bone of the skull. This downward 3 and forward displacement can result in up to pituitary tumor, sphenoid mucocele, metastatic 30% of pseudotumor cerebri patients tumors), vascular problems (carotid-cavernous exhibiting either unilateral or bilateral thrombosis, carotid-cavernous fistula, dural abducens