Ocular Motor Signs in Brainstem Demyelinating Disease - Spontaneous Upbeat, Vertical Gaze-Evoked Nystagmus, Slow Saccades, Bilateral Vestibular Loss, INOs

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: This is a 25-year-old woman who presented with painful vision loss bilaterally two years prior to this video recording, which was diagnosed as optic neuritis. Months later, she experienced oscillopsia and binocular horizontal diplopia and was subsequently diagnosed with multiple sclerosis. No records were available regarding previous examinations. At the time of this video recording, her exam was as follows: visual acuities of 20/60 OD and 20/125 OS with a mild relative afferent pupillary defect OS. Ishihara plates were 15/16 OD and 13/16 OS and there was mild temporal pallor OU. Visual fields were intact to confrontation. On ocular motor and vestibular examination, adduction deficits (OD>OS) were noted in both eyes in addition to abducting nystagmus OU with lateral gaze. There was an 8 prism diopter (PD) exotropia (XT) in primary gaze, which increased to 20 PD XT in right gaze and 25 PD XT in left gaze. Adduction deficits could not be overcome by convergence. In primary gaze, there was spontaneous upbeat nystagmus (UBN), and there was gaze-evoked nystagmus vertically (UBN in up gaze and downbeat in down gaze). Saccades were mild to moderately slow horizontally more than vertically, and adducting saccades were slower than abducting saccades. When taking into account her nystagmus, pursuit and vestibulo-ocular reflex (VOR) suppression appeared to be normal. There were poor fast phases to an optokinetic stimulus. The visually-enhanced vestibulo-ocular reflex appeared to be normal, and there were intermittent catch-up saccades noted with head impulse test horizontally and vertically. Salient findings included the following, which could be correlated with MRI hyperintensities throughout the brainstem (no involvement of the cerebellum): 1) Spontaneous UBN: this caused vertical oscillopsia that was independent of head movements. UBN often localizes to the dorsal caudal medulla (nucleus of Roller and nucleus intercalatus), and in fact, hyperintense T2/FLAIR signal was present bilaterally in this region (see arrows in figure). Visual acuities were impaired in part due to bilateral optic neuritis, but also given her spontaneous nystagmus. 2) Hypoactive VOR: this caused oscillopsia that depended on head movements (e.g., walking) and bilateral vestibular loss was shown on bedside and video head impulse testing (HIT). Afferents from the horizontal semicircular canals (SCC) synapse in the medial vestibular nucleus (hyperintense T2/FLAIR signal was present in the region of the MVN-nucleus prepositus hypoglossi complex bilaterally; see arrows in figure), while afferents from the vertical SCC synapse on other vestibular subnuclei that in turn project rostrally via the medial longitudinal fasciculus (MLF) to the trochlear and oculomotor nuclei. Bilateral dorsal pontine hyperintense T2/FLAIR signal was present in the region of the MLFs (see arrows in the figure). 3) Bilateral adduction paresis: this was responsible for horizontal diplopia from bilateral internuclear ophthalmoplegia (INO) with adduction deficits and abducting nystagmus OU from bilateral lesions in the MLF. Notably, even when unilateral or bilateral INOs are present, HIT/video HIT in the plane of the horizontal SCCs is typically normal/near normal. As an example, a patient with a right INO can have a right adduction deficit (or lag) with leftward gaze. However, when a HIT is performed to the right (requiring activation of the right medial rectus), the afferents from the horizontal SCC can bypass the MLF lesion (via the ascending tract of Deiters), allowing for preservation of the efferent limb of the horizontal VOR. In this patient's case, hypofunction in the planes of the horizontal SCC could be explained by bilateral MVN lesions. 4) Vertical gaze-evoked nystagmus: this was due to vertical gaze holding impairment from either lesions in the interstitial nucleus of Cajal (INC) involvement in the rostral midbrain (see arrows in figure), or from lesions in the medially located pontomedullary paramedian tracts (receive vertical gaze holding signals from INC and relay to cerebellar flocculus). 5) Slow horizontal saccades: while the slow adducting saccades could be explained by bilateral INOs, the abducting saccades were also slow and fast phases were poor with an optokinetic stimulus. Vertical saccades appeared to be normal when taking into account her significant UBN. Given widespread dorsal pontine disease (see arrows in figure on sagittal FLAIR), it is likely that paramedian pontine reticular formation (PPRF) was involved. There was no contrast enhancement on MRI, although symptoms had been stable for several years by that point. Given extensive dorsal brainstem involvement, neuromyelitis optica (NMO) should be a strong consideration, although evaluation was more consistent with MS given typical supratentorial periventricular lesions and negative NMO testing. 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: Salient findings included the following, which could be correlated with MRI hyperintensities throughout the brainstem (no involvement of the cerebellum): 1) Spontaneous UBN: this caused vertical oscillopsia that was independent of head movements. UBN often localizes to the dorsal caudal medulla (nucleus of Roller and nucleus intercalatus), and in fact, hyperintense T2/FLAIR signal was present bilaterally in this region (see arrows in figure). Visual acuities were impaired in part due to bilateral optic neuritis, but also given her spontaneous nystagmus. 2) Hypoactive VOR: this caused oscillopsia that depended on head movements (e.g., walking) and bilateral vestibular loss was shown on bedside and video head impulse testing (HIT). Afferents from the horizontal semicircular canals (SCC) synapse in the medial vestibular nucleus (hyperintense T2/FLAIR signal was present in the region of the MVN-nucleus prepositus hypoglossi complex bilaterally; see arrows in figure), while afferents from the vertical SCC synapse on other vestibular subnuclei that in turn project rostrally via the medial longitudinal fasciculus (MLF) to the trochlear and oculomotor nuclei. Bilateral dorsal pontine hyperintense T2/ FLAIR signal was present in the region of the MLFs (see arrows in the figure). 3) Bilateral adduction paresis: this was responsible for horizontal diplopia from bilateral internuclear ophthalmoplegia (INO) with adduction deficits and abducting nystagmus OU from bilateral lesions in the MLF. Notably, even when unilateral or bilateral INOs are present, HIT/video HIT in the plane of the horizontal SCCs is typically normal/near normal. As an example, a patient with a right INO can have a right adduction deficit (or lag) with leftward gaze. However, when a HIT is performed to the right (requiring activation of the right medial rectus), the afferents from the horizontal SCC can bypass the MLF lesion (via the ascending tract of Deiters), allowing for preservation of the efferent limb of the horizontal VOR. In this patient's case, hypofunction in the planes of the horizontal SCC could be explained by bilateral MVN lesions. 4) Vertical gaze-evoked nystagmus: this was due to vertical gaze holding impairment from either lesions in the interstitial nucleus of Cajal (INC) involvement in the rostral midbrain (see arrows in figure), or from lesions in the medially located pontomedullary paramedian tracts (receive vertical gaze holding signals from INC and relay to cerebellar flocculus). 5) Slow horizontal saccades: while the slow adducting saccades could be explained by bilateral INOs, the abducting saccades were also slow and fast phases were poor with an optokinetic stimulus. Vertical saccades appeared to be normal when taking into account her significant UBN. Given widespread dorsal pontine disease (see arrows in figure on sagittal FLAIR), it is likely that paramedian pontine reticular formation (PPRF) was involved. https://collections.lib.utah.edu/ark:/87278/s64517rm