Reversal of Vertical Nystagmus with Convergence in Anti-DPPX Encephalitis

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: This is a man who initially presented with spontaneous upbeat and torsional nystagmus, which led to the diagnosis of anti-DPPX encephalitis (for further details on this patient's course and for a video of his nystagmus, see reference 1). Over 6-12 months, his spontaneous (mainly) upbeat nystagmus (UBN) transitioned to spontaneous downbeat nystagmus (DBN). In this video, he has gaze-evoked nystagmus (e.g., right-beating in right gaze and left-beating nystagmus in left gaze) with a downbeat component. While spontaneous downbeat nystagmus was present in primary gaze, with convergence, this transitioned to upbeat nystagmus. Vertical nystagmus reversing with convergence is a finding often seen in patients with Wernicke's encephalopathy. While the semicircular canals (posterior, horizontal, and anterior) are the angular acceleration detectors in the labyrinth, the otoliths (utricle and saccule) are the linear acceleration detectors and are responsible for the translational vestibulo-ocular reflex (t-VOR). In order for the t-VOR to generate appropriate eye movements, orbital position and vergence angle must be taken into account(2). Brainstem structures responsible for processing otolithic inputs include the medial and inferior vestibular nuclei (MVN and LVN), which have projections to the cerebellar nodulus (which also has a role in modulating the t-VOR)2. In patients with acute Wernicke's encephalopathy(2), gaze-evoked nystagmus can be attributed to damage involving the MVN-nucleus prepositus hypoglossi (NPH) complex, while the horizontal (angular) VOR is commonly impaired since the horizontal semicircular canal afferents synapse in the MVN. With Wernicke's the transition from spontaneous upbeat nystagmus (attributed to damage involving the nucleus of Roller and nucleus intercalatus, which both inhibit the flocculus) to downbeat nystagmus with convergence can also be explained by damage to the MVN and LVN given their role in the t-VOR. In this patient with anti-DPPX encephalitis, impairment of MVN-LVN and/or nodulus are all possible explanation or the transition of DBN to UBN with convergence. It is possible that the initial spontaneous upbeat-torsional nystagmus resulted from asymmetric pontomedullary damage involving the vertical semicircular canal (SCC) pathways (multiple MRIs showed no clear T2/FLAIR or T1-enhancing posterior fossa lesions). Several theories exist for the transition of spontaneous UBN to spontaneous DBN: 1) Given the proximity of the paramedian tract nuclei (PTN), the chronic downbeat nystagmus could relate to vertical SCC pathway recovery with persistent PTN damage - i.e., a similar mechanism to the prevailing theory for transition of acute UBN to chronic DBN in Wernicke's encephalopathy. Since the PTN normally excites the flocculus, damage to the PTN can cause relative hypoactivity of the flocculus and an upward bias (slow phase drift since anterior canal [upward or anti-gravity] pathways are overactive) with resultant downbeat nystagmus. 2) The patient also developed gaze-evoked nystagmus in lateral and up and down gaze after 6-12 months, likely related to dysfunction of the flocculus/paraflocculus rather than the MVN-NPH given its presence in horizontal and vertical gaze. The spontaneous DBN and saccadic pursuit and VOR suppression that also developed are also suggestive of a flocculus/paraflocculus syndrome. It is therefore possible that the acute asymmetric vertical SCC pathway injury recovered, but flocculus/paraflocculus impairment developed chronically. 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: This is a man who initially presented with spontaneous upbeat and torsional nystagmus, which led to the diagnosis of anti-DPPX encephalitis. Over 6-12 months, his spontaneous (mainly) upbeat nystagmus (UBN) transitioned to spontaneous downbeat nystagmus (DBN). In this video, he has gaze-evoked nystagmus (e.g., right-beating in right gaze and left-beating nystagmus in left gaze) with a downbeat component. While spontaneous downbeat nystagmus was present in primary gaze, with convergence, this transitioned to upbeat nystagmus. Vertical nystagmus reversing with convergence is a finding often seen in patients with Wernicke's encephalopathy. While the semicircular canals (posterior, horizontal, and anterior) are the angular acceleration detectors in the labyrinth, the otoliths (utricle and saccule) are the linear acceleration detectors and are responsible for the translational vestibulo-ocular reflex (t-VOR). In order for the t-VOR to generate appropriate eye movements, orbital position and vergence angle must be taken into account. Brainstem structures responsible for processing otolithic inputs include the medial and inferior vestibular nuclei (MVN and LVN), which have projections to the cerebellar nodulus (which also has a role in modulating the t-VOR). In patients with acute Wernicke's encephalopathy, gaze-evoked nystagmus can be attributed to damage involving the MVN-nucleus prepositus hypoglossi (NPH) complex, while the horizontal (angular) VOR is commonly impaired since the horizontal semicircular canal afferents synapse in the MVN. With Wernicke's the transition from spontaneous upbeat nystagmus (attributed to damage involving the nucleus of Roller and nucleus intercalatus, which both inhibit the flocculus) to downbeat nystagmus with convergence can also be explained by damage to the MVN and LVN given their role in the t-VOR. In this patient with anti-DPPX encephalitis, impairment of MVN-LVN and/or nodulus are all possible explanation for the transition of DBN to UBN with convergence. It is possible that the initial spontaneous upbeat-torsional nystagmus resulted from asymmetric pontomedullary damage involving the vertical semicircular canal (SCC) pathways (multiple MRIs showed no clear T2/FLAIR or T1-enhancing posterior fossa lesions). Several theories for the transition of spontaneous UBN (acutely) to spontaneous DBN (chronically) in this patient include: 1) Given the proximity of the paramedian tract nuclei (PTN), the chronic downbeat nystagmus could relate to vertical SCC pathway recovery with persistent PTN damage - i.e., a similar (or identical) mechanism to the prevailing theory for transition of acute UBN to chronic DBN in Wernicke's encephalopathy. Since the PTN normally excites the flocculus, damage to the PTN can cause relative hypoactivity of the flocculus and an upward bias (slow phase drift since anterior canal [upward or anti-gravity] pathways are overactive) with resultant downbeat nystagmus. 2) The patient also developed gaze-evoked nystagmus in lateral and up and down gaze after 6-12 months, likely related to dysfunction of the flocculus/ paraflocculus rather than the MVN-NPH given its presence in horizontal and vertical gaze. The spontaneous DBN and saccadic pursuit and VOR suppression that also developed are also suggestive of a flocculus/paraflocculus syndrome. It is therefore possible that the acute asymmetric vertical SCC pathway injury recovered, but flocculus/paraflocculus impairment developed chronically. https://collections.lib.utah.edu/ark:/87278/s6bg75c3