Editors' note: Impaired vestibular responses in internuclear ophthalmoplegia: Association and dissociation

Abstract

In “Impaired vestibular responses in internuclear ophthalmoplegia: Association and dissociation,” Choi et al. determined that the medial longitudinal fasciculus (MLF) serves as the main passage for the high-acceleration vestibulo-ocular reflex (VOR) from the contralateral posterior canal. They also concluded that the associations and dissociations of the vestibular dysfunction indicate variable combinations of damage to the vestibular fibers ascending or descending in the MLF in strokes causing isolated unilateral internuclear ophthalmoplegia (INO). Dr. Johnston raises concerns regarding these conclusions. Based on her experience, horizontal VOR latencies are normal in patients with INO, implying integrity of direct VOR. She explained that undamaged fibers in MLF or extrafascicular pathways can still initiate the VOR without delay. Dr. Kim, senior author of the study, points out, in Dr. Johnston's study, that the VOR was recorded only in the eye on the lesion side by adopting lower velocity and acceleration of head motion and did not specify the lesion extent or INO as an isolated finding. He also adds that her suggestion does not explain the preservation of the head impulse VOR for the ipsilesional anterior canal in the presence of impairments for other canals, and impaired VOR gains in the eye on the contralesional side in patients with strictly isolated unilateral INO. These findings support separate brainstem pathways for posterior and anterior canal projections pertaining to high acceleration stimuli. In “Impaired vestibular responses in internuclear ophthalmoplegia: Association and dissociation,” Choi et al. determined that the medial longitudinal fasciculus (MLF) serves as the main passage for the high-acceleration vestibulo-ocular reflex (VOR) from the contralateral posterior canal. They also concluded that the associations and dissociations of the vestibular dysfunction indicate variable combinations of damage to the vestibular fibers ascending or descending in the MLF in strokes causing isolated unilateral internuclear ophthalmoplegia (INO).