Preferential Impairment of the Contralesional Posterior Semicircular Canal in Internuclear Ophthalmoplegia

Abstract

BackgroundThe vertical vestibulo-ocular reflex (VOR) may be impaired in internuclear ophthalmoplegia (INO) as the medial longitudinal fasciculus (MLF) conveys VOR-signals from the vertical semicircular canals. It has been proposed that signals from the contralesional posterior semicircular canal (PSC) are exclusively transmitted through the MLF, while for the contralesional anterior canal other pathways exist.ObjectiveHere, we aimed to characterize dysfunction in individual canals in INO-patients using the video-head-impulse test (vHIT) and to test the hypothesis of dissociated vertical canal impairment in INO.MethodsVideo-head-impulse testing and magnetic resonance imaging were obtained in 21 consecutive patients with unilateral (n = 16) or bilateral (n = 5) INO and 42 controls. VOR-gains and compensatory catch-up saccades were analyzed and the overall function (normal vs. impaired) of each semicircular canal was rated.ResultsIn unilateral INO, largest VOR-gain reductions were noted in the contralesional PSC (0.55 ± 0.11 vs. 0.89 ± 0.08, p < 0.001), while in bilateral INO both posterior (0.43 ± 0.11 vs. 0.89 ± 0.08, p < 0.001) and anterior (0.58 ± 0.19 vs. 0.88 ± 0.09, p < 0.001) canals showed marked drops. Small, but significant VOR-gain reductions were also found in the other canals in unilateral and bilateral INO-patients. Impairment of overall canal function was restricted to the contralesional posterior canal in 60% of unilateral INO-patients, while isolated involvement of the posterior canal was rare in bilateral INO-patients (20%). Reviewers correctly identified the INO-pattern in 15/21 (71%) patients and in all controls (sensitivity = 84.2% [95%-CI = 0.59.5–95.8]; specificity = 95.5% [95%-CI = 83.3–99.2]).ConclusionUsing a vHIT based overall rating of canal function, the correct INO-pattern could be identified with high accuracy. The predominant and often selective impairment of the contralesional posterior canal in unilateral INO further supports the role of the MLF in transmitting posterior canal signals. In patients with acute dizziness and abnormal vHIT-results, central pathologies such as INO should be considered as well, especially when the posterior canal is involved.

Greater Disability Is Associated with Worse Vestibular and Compensatory Oculomotor Functions in People Living with Multiple Sclerosis

“…Our findings in PLW-MS, nearly all of whom had clinical evidence of brainstem involvement, are in agreement with the extend prior studies that reveal a similar pattern of graduated involvement of the lateral, anterior, and posterior SCC pathways in adults who have evidence of INO associated with medial longitudinal fasciculus lesions on magnetic resonance imaging [ 23 , 24 ]. In a cohort of adults with brainstem infarcts or demyelination that was associated with INO, the results, which were obtained from a vHIT system not unlike the system we used, revealed that a VOR gain reduction was more pronounced for the contralesional posterior SCC than the ipsilateral lateral and anterior SCCs in unilateral INO [ 24 ]. It is of note that PLW-MS who have either unilateral or bilateral INO have been shown to have asymmetrical ipsilesional VOR deficits and that the VOR gain is lower for the adducting compared to the abducting eye when the eye movement is measured binocularly using search coils [ 23 ].…”

“…In response to lateral head impulses, PLW-MS have been shown to recruit CSs less often and with a slightly longer latency than persons who are status-post unilateral vestibular deafferentation [ 19 ] but more often with a reduced latency relative to healthy controls [ 21 , 22 ]. PLW-MS who have documented infratentorial lesions [ 23 , 24 ] and with suspected occult [ 18 ] internuclear ophthalmoplegia (INO) are reported to have asymmetrical abnormal VOR gains.…”

“…To date, only the VOR gain and CS frequency from six-canal vHIT have been reported in investigations of the vestibular function and compensatory oculomotor behavior in PLW-MS [ 7 , 23 , 24 ]. Additionally, few studies have investigated the association between the tests of the SCC function and MS-related disability [ 25 ].…”

Eye Movement Abnormalities in Multiple Sclerosis: Pathogenesis, Modeling, and Treatment

“…The latter is a combination of skew deviation, contralateral head tilt and ocular torsion, and reflects dysfunction of vestibular reactions in the roll plane ( 11 ). The role of the MLF in carrying exclusively contralateral posterior semicircular canal signals is confirmed by studies that combine MRI and the video-head-impulse test ( 12 ). Patients with unilateral INO may have vertical diplopia due to a non-evident skew deviation, which can be relieved by using a small vertical prism.…”

Vertigo Due to Vascular Mechanisms

“…[55][56][57] Among these, upbeat, seesaw nystagmus, and contraversive OTR and SVV tilt and impairment of the vertical VOR may occur as well as abnormal cervical and ocular VEMP responses. [55][56][57] Ten patients with INO due to strokes showed a prominent decrease in the VOR gain for the contralesional posterior canal during HITs. 55 The MLF may serve as the pathway for high acceleration VOR from the contralateral posterior canal.…”