Periodic Alternating Nystagmus and Central Head-Shaking Nystagmus from Nodulus Injury

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: This is a 35-year-old man who suffered a gunshot wound to his cerebellum. When he regained consciousness days later, he experienced oscillopsia due to periodic alternating nystagmus (PAN). He was started on baclofen 10 mg bid, and had a dramatic response and only had moderate spontaneous left-beating nystagmus (without PAN) along with gaze-evoked nystagmus. The dose was increased to 20 mg 4 times/day, at which time nystagmus and oscillopsia resolved completely (without sedation). However, following 10-15 seconds of 2-3 Hz horizontal head-shaking, there was robust left-beating nystagmus. This could be explained by injury to the nodulus, a localization that explains both PAN and certain central patterns of head-shaking nystagmus (HSN) such as this (i.e., robust HSN in the absence of unilateral vestibular loss). Neuronal circuits responsible for velocity storage (which normally prolong the vestibulo-ocular reflex response beyond the mechanical limitations of the semicircular canal cupula) are mainly located in the vestibular nucleus and nodulus. Disinhibition of velocity storage due to nodulus injury can therefore contribute to PAN or central HSN as in this case. 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: This patient suffered a gunshot wound to the cerebellum. When he regained consciousness days later, he experienced oscillopsia due to periodic alternating nystagmus (PAN). He was started on baclofen 10 mg bid, and had a dramatic response and only had moderate spontaneous left-beating nystagmus (without PAN) along with gaze-evoked nystagmus. The dose was increased to 20 mg 4 times/day which was tolerated well, and nystagmus and oscillopsia resolved completely. However, following 10-15 seconds of 2-3 Hz horizontal head-shaking, there was robust left-beating nystagmus. This could be explained by injury to the nodulus, a localization that explains both PAN and certain central patterns of head-shaking nystagmus (HSN) such as this (i.e., robust HSN in the absence of unilateral vestibular loss). Neuronal circuits responsible for velocity storage (which normally prolong the vestibulo-ocular reflex response beyond the mechanical limitations of the semicircular canal cupula) are mainly located in the vestibular nucleus and nodulus. Disinhibition of velocity storage due to nodulus injury can therefore contribute to PAN or central HSN as in this case. https://collections.lib.utah.edu/ ark:/87278/s64b892v