Upbeat Nystagmus in Dorsolateral Pontine Infarction

Clinical Correspondence Section Editors: Robert Avery, DO Karl C. Golnik, MD Upbeat Nystagmus in Dorsolateral Pontine Infarction Tzu-Pu Chang, MD, David S. Zee, MD, Daniel R. Gold, DO U Downloaded from http://journals.lww.com/jneuro-ophthalmology by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 05/04/2022 pbeat nystagmus (UBN) is usually caused by lesions involving the paramedian brainstem including the perihypoglossal nuclei, medial longitudinal fasciculus, or ventral tegmental tract (1,2). Interruption of the pathway from anterior semicircular canal to superior vestibular nucleus to extraocular elevator muscles (superior rectus [SR] and inferior oblique [IO]) via the brachium conjunctivum can also theoretically cause UBN, but previous reports attributing UBN to brachium conjunctivum injury had larger or multiple lesions involving other anatomical structures (3). Here we report a patient with UBN whose MRI showed an acute infarct in the left dorsolateral pons involving the rostral portion of left superior vestibular nucleus. A 65-year-old man came to the emergency department (ED) with vertigo and unsteadiness. In the ED, he had spontaneous upbeat nystagmus (UBN) with a torsional component (fast phase with top poles beating toward the right ear) that was most prominent in right gaze (video can be accessed at https://collections.lib.utah.edu/ark:/87278/ s6kx02v4). Neurologic examination was otherwise intact. By 3 days after symptom onset, his UBN had resolved. The video head impulse test (vHIT; EyeSeeCam, Fürstenfeldbruck, Germany) showed normal vestibulo-ocular reflexes (VOR) in all 6 semicircular canals. He could walk without support but veered to the right side. The brain MRI 2 days after onset demonstrated a small left dorsolateral pontine hyperintensity on diffusion-weighted imaging (Fig. 1A) and T2/FLAIR (Fig. 1B), involving the left superior vestibular nucleus (SVN). Although downbeat nystagmus (DBN) is almost always cerebellar in origin, UBN is nearly always caused by a brainstem lesion. The most commonly reported localization for UBN is the caudal medial medulla (1,4). FIG. 1. A. MR with diffusion-weighted imaging, and B. FLAIR demonstrates a hyperintense lesion in the left dorsolateral pons, involving the left rostral SVN. BC, brachium conjunctivuml; MLF, medial longitudinal fasciculus; SVN, superior vestibular nucleus. Department of Neurology (T-PC), Neuro-medical Scientific Center, Taichung Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan; Department of Neurology (T-PC), School of Medicine, Tzu Chi University, Hualien, Taiwan; and Department of Neurology (DRG, DSZ), Johns Hopkins University School of Medicine, Baltimore. The authors report no conflicts of interest. Address correspondence to Daniel R. Gold, DO, Department of Neurology, Johns Hopkins University School of Medicine, 600 N. Wolfe St, Pathology 2-210, Baltimore, MD 21287; E-mail: [e-mail] e94 In this area, the nucleus intercalatus of Staderini, nucleus of Roller, or nucleus pararaphales of the paramedian tract are located, suggesting that the pathophysiology of the UBN relates to an impaired neural integrator for vertical gaze holding. UBN is also commonly seen with acute medial longitudinal fasciculus (MLF) lesions. The MLF includes pathways that originated in the contralateral vertical semicircular canals (anterior canal [AC] and posterior canal [PC]) and utricle, with AC and PC afferents Chang et al: J Neuro-Ophthalmol 2021; 41: e94-e96 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence leaving the labyrinth and first synapsing in the ipsilateral medical vestibular nucleus (MVN). They then decussate and ascend through the contralateral MLF, projecting to innervate the cyclovertical elevator (AC) or depressor (PC) muscles. MLF injury can preferentially involve 1) AC afferents causing UBN (more in the contralesional eye) and ipsiversive torsional nystagmus; 2) PC afferents causing DBN (more in the ipsilesional eye) and ipsiversive torsional nystagmus; or 3) can equally affect AC and PC (and/or utriculo-ocular motor) pathways causing a jerky seesaw pattern of nystagmus (UBN in one eye and DBN in the other) (5). An acute MLF lesion will commonly cause an internuclear ophthalmoplegia and skew deviation as well (resulting from involvement of the interneurons connecting sixth nucleus to contralateral medial rectus subnucleus and utricle pathways, respectively), making localization of this variety of UBtorsional nystagmus straightforward. In addition to the MVN-MLF pathway, 2 additional pathways carrying AC afferents have been confirmed in animal studies (1). Anterior canal fibers also project to the caudal SVN, which then cross the midline of the rostral medulla and ascend through the ventral tegmental tract (VTT) to the oculomotor subnuclei (SR and IO). In the third pathway, fibers from the rostral portion of the SVN course dorsally and join the brachium conjunctivum (BC, also known as the superior cerebellar peduncle), and then upward to the oculomotor subnuclei (SR and IO). In contrast to the single pathway that carries PC afferents (MVNMLF), these 3 pathways (MVN-MLF, caudal SVN-VTT, and rostral SVN-BC) jointly convey fibers responsible for the AC VOR. In our case, the UBN appeared more torsional during right gaze, in the canal plane of the left AC. MRI showed a small stroke involving the left SVN in the lateral pons, compatible with damage to the rostral SVN-BC pathway. FIG. 2. Excitatory VOR pathways of anterior semicircular canal with additional labels highlighting the mirror location of lesion site. The neurons in the rostral portion of SVN receive signals from anterior canal and project to oculomotor nucleus through BC, which contribute to one of the 3 anterior canal VOR pathways. Damage of the neurons result in upbeat nystagmus. III, oculomotor nucleus; IV, trochlear nucleus; BC, brachium conjunctivum; IR, inferior rectus; IO, inferior oblique; INC, interstitial nucleus of Cajal; LVN, lateral vestibular nucleus; MVN, medial vestibular nucleus; SR, superior rectus; SO, superior oblique; SVN, superior vestibular nucleus; VOR, vestibulo-ocular reflexes; VTT, ventral tegmental tract. Source: Neuro-Ophthalmology Virtual Education Library: NOVEL (online) Available from: https://collections.lib.utah.edu/ark:/87278/s6xq1s4t. Accessed September 2019. Chang et al: J Neuro-Ophthalmol 2021; 41: e94-e96 e95 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence Three days after symptom onset, AC and PC VOR testing through vHIT did not show an abnormality in the plane of the left AC. This may be because the VOR impairment had recovered (or was compensated for centrally) or because the other 2 pathways (MVN-MLF and caudal SVN-VTT) remained intact (Fig. 2). Our case not only demonstrates that a lateral pontine lesion can cause UBN, but provides further support for a rostral SVN-BC pathway contributing to the AC VOR in humans. In the future, the UBN caused by damage to the AC VOR pathways (e.g., this case) and the UBN associated with an abnormal neural integrator (e.g., pure UBN in Wernicke’s encephalopathy) will need to be clarified, especially as pharmacological treatment approaches may differ. The presence or absence of a torsional component in patients with UBN may be an important clue to the localization because UB-torsional e96 nystagmus would be expected with unilateral AC VOR pathway involvement. REFERENCES 1. Leigh RJ, Zee DS. The Neurology of Eye Movements. Oxford, UK: Oxford University Press, 2015. 2. Fisher A, Gresty M, Chambers B, Rudge P. Primary position upbeating nystagmus. A variety of central positional nystagmus. Brain. 1983;106:949–964. 3. Tilikete C, Milea D, Pierrot-Deseilligny C. Upbeat nystagmus from a demyelinating lesion in the caudal pons. J Neuroophthalmol. 2008;28:202–206. 4. Hirose G, Ogasawara T, Shirakawa T, Kawada J, Kataoka S, Yoshioka A, Halmagyi GM. Primary position upbeat nystagmus due to unilateral medial medullary infarction. Ann Neurol. 1998;43:403–406. 5. Jeong SH, Kim EK, Lee J, Choi KD, Kim JS. Patterns of dissociate torsional-vertical nystagmus in internuclear ophthalmoplegia. Ann N Y Acad Sci. 2011;1233:271–278. Chang et al: J Neuro-Ophthalmol 2021; 41: e94-e96 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.