Amadeo R. Rodriguez, MD,
Robert A. Egan, MD and
Jason J.S. Barton, MD, PhD, FRCPC
From the Departments of Medicine (Neurology) and Ophthalmology and Visual Sciences (A.R.R., J.J.S.B.), University of British Columbia, Vancouver, Canada; and Neuro-Ophthalmology (R.A.E.), St. Helena Neurology, St. Helena, CA.
Address correspondence and reprint requests to Dr. Amadeo R. Rodriguez, Neuro-ophthalmology Section D, VGH Eye Care Centre, 2550 Willow Street, Vancouver, BC, Canada V5Z 3N9 arrodr{at}gmail.com
In skew deviation, one eye is higher than the other, causingvertical diplopia. Skew deviation is a prenuclear disorder resultingfrom imbalance in otolith input to the oculomotor system, producedby unilateral lesions anywhere from the otoliths to the interstitialnucleus of Cajal in the rostral midbrain,1 and as such is onecomponent of the ocular tilt reaction.2,3 We report a womanwith a history of fluctuating diplopia after resection of aleft thalamic angioma. She was shown to have intermittent paroxysmalocular tilt reaction episodes superimposed on a tonic oculartilt reaction.
A 64-year-old woman initially presented at age 55 with malaise,headache, and imbalance, leading to the discovery on neuroimagingof a vascular malformation in the left thalamus. Following resection,she had persistent vertical diplopia on downgaze, and episodesseveral times a day of vertical diplopia in other gaze positions,associated with a sense of twisting of her eyes. For 9 yearsshe had been on both gabapentin and carbamazepine, with uncertaineffect: she reported some modest reduction in episodes withincreasing the dose of gabapentin from 600 mg/day to 1,200 mg/day.Visual acuity, tests of color vision with pseudo-isochromaticplates, visual fields by confrontation, pupils, and fundus examinationshad normal results. Palpebral fissures were symmetric. Ductionswere full in all directions. Fixation was steady. Pursuit andcancellation of the vestibulo-ocular reflex were normal. Saccadeswere rapid and accurate. Cover testing showed that she was orthophoricin primary position (i.e., eyes aligned in straight-ahead gaze)but had a small 3-prism diopter left hypertropia in downgaze.Maddox wing testing showed a small 1-degree excyclotropia (topof the eyes rotated away from each other). She had a right headtilt. The remainder of the neurologic examination had normalresults. During her examination, she developed episodes of conjugatecounterclockwise torsion (i.e., the upper pole of both eyestilted toward her left shoulder) with right hypertropia, lasting1 to 3 seconds, at variable intervals (see video).
MRI showed a large cavernous hemangioma in the left meso-diencephalicjunction (figure).
Ocular tilt reaction consists of skew deviation, ocular torsion,head tilt, and deviation of the subjective visual vertical,all tilted toward the lower (hypotropic) eye,2,3 with the sideof the tilt named for the side of the hypotropic eye. It canbe produced experimentally by stimulation of the utricular nerve,4and represents a normal otolithic-ocular response to lateraldisplacement of the linear acceleration vector, as happens whenone travels around a curve in a vehicle. The pathway for theotolithic-ocular response projects from the vestibular end-organto the vestibular nuclei in the medulla and on to the interstitialnucleus of Cajal in the midbrain. This pathway decussates inthe pons: hence static ocular tilt reactions from hypofunctionare ipsiversive (lower eye on the side of the lesion) with peripheralvestibular and pontomedullary lesions and contraversive withpontomesencephalic lesions.1 The direction of the deviationproduced by paroxysmal hyperfunction in this pathway (i.e.,irritative lesions), on the other hand, is in the opposite direction.5,6Our patient, who has a lesion in the vicinity of the left interstitialnucleus of Cajal, illustrates this point. She has a tonic righthead tilt and mild left hypertropic skew deviation, which representsa partial ocular tilt reaction—partial in that there isno significant torsion at baseline—that is contraversivewith respect to the lesion (head is tilted away from the sideof the lesion). Superimposed on this, she develops paroxysmalepisodes of left ocular tilt reaction, with a right hypertropicskew deviation and counterclockwise torsion.
Paroxysmal ocular tilt reaction is distinctly rare. One patientwith multiple sclerosis had pendular nystagmus and a paroxysmalocular tilt reaction that improved with carbamazepine.5 Anotherpatient with a lesion in the vicinity of the left interstitialnucleus of Cajal presented with right hypertropia, conjugatetorsion, left head tilt, and nystagmoid eye movements.6 Threepatients were described with episodic ocular torsion and skewdeviation due to mesodiencephalic lesions, in whom the conjugateocular torsion was initiated by a torsional fast eye movement.7Similar to our case, one of these patients had a cavernoma inthe right mesodiencephalic region: there was a baseline ipsilateralhypertropic skew deviation with episodes of clockwise oculartorsion and dystonic movements in the contralateral limbs. Suchvascular lesions may be particularly likely to produce bothtonic hypofunction and transient hyperfunction.
Ocular tilt reaction is a prenuclear disorder due to imbalancein otolithic pathways anywhere from the vestibular organ tothe midbrain.
Ocular tilt reaction is the triad of 1) skewdeviation, a prenuclearvertical misalignment of the eyes, 2)head tilt toward the hypotropiceye, and 3) ocular torsion.If all three components are present,ocular tilt reaction iscomplete. Partial forms also exist.
Ocular torsion in oculartilt reaction usually consists of incyclotorsionof the uppereye (the upper pole of the eye is rotated nasally)with excyclotorsionof the lower eye (the upper pole of theeye is rotated temporally);thus, the tops of both eyes arerotated toward the lower ear.(In contrast, IV nerve palsy,the most common cause of verticalmisalignment, involves excyclotorsionof the upper eye.)
Asthe pathway for the otolithic-ocular response decussatesinthe pons, lesions of the lower pons/medulla cause an ipsiversive(ipsilateral eye is hypotropic) ocular tilt reaction, whereaslesions of the upper pons/midbrain cause a contraversive one.
Whereas most cases of ocular tilt reaction are tonic and dueto a decrease in tonic neural activity, paroxysmal ocular tiltreaction is due to intermittent unilateral hyperfunction, withtilt in the direction opposite to that of tonic ocular tiltreactions.
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CASE REPORT
DISCUSSION
