Pseudo-Spontaneous Nystagmus and Bow and Lean Test in Horizontal Canal BPPV

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻:This is a 70-year-old woman presenting to the Emergency Department with positional vertigo that was determined to be due to the apogeotropic variant of right horizontal canal (HC) benign paroxysmal positional vertigo (BPPV). When her head is in a neutral position with the head in axis with the trunk, there is a pseudo-spontaneous nystagmus. The term ‘pseudo-spontaneous' is used because the nystagmus is created by otoconia within the HC sliding down to the most dependent portion of the canal, owing to its orientation - i.e., the most anterior portion of the HC is at about 20-30 degree higher than the posterior portion. Therefore, some patients with HC-BPPV may have an unprovoked ‘pseudo-spontaneous' nystagmus (unrelated to damage to the vestibular system) when the head is in a neutral position. In the case of right apogeotropic HC BPPV, leaning the head backward (the lean portion of the bow and lean test) will cause otoconial particles to slide posteriorly in an ampullopetal (excitatory) direction, which will generate a (strong) slow phase to the left and a fast phase to the right (right-beating nystagmus toward the affected ear). Because the orientation of the HC is in a similar (but less vertical) position with the head in axis with the trunk, for the same reasons, the pseudo-spontaneous nystagmus will be right-beating (toward the affected ear). Bowing the head forward (the bow portion of the bow and lean test) will cause otoconial particles to slide anteriorly in an ampullofugal (inhibitory) direction, creating a (weak) slow phase to the right and a fast phase to the left (left-beating nystagmus toward the healthy ear). 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: This is a 70-year-old woman presenting to the Emergency Department with positional vertigo that was determined to be due to the apogeotropic variant of right horizontal canal (HC) benign paroxysmal positional vertigo (BPPV). When her head is in a neutral position with the head in axis with the trunk, there is a pseudo-spontaneous nystagmus. The term "pseudospontaneous" is used because the nystagmus is created by otoconia within the HC sliding down to the most dependent portion of the canal, owing to its orientation-i.e., the most anterior portion of the HC is at about 20-30 degree higher than the posterior portion. Therefore, some patients with HC-BPPV may have an unprovoked "pseudo-spontaneous" nystagmus (unrelated to damage to the vestibular system) when the head is in a neutral position. In the case of right apogeotropic HC BPPV, leaning the head backward (the lean portion of the bow and lean test) will cause otoconial particles to slide posteriorly in an ampullopetal (excitatory) direction, which will generate a (strong) slow phase to the left and a fast phase to the right (right-beating nystagmus toward the affected ear). Because the orientation of the HC is in a similar (but less vertical) position with the head in axis with the trunk, for the same reasons, the pseudo-spontaneous nystagmus will be right-beating (toward the affected ear). Bowing the head forward (the bow portion of the bow and lean test) will cause otoconial particles to slide anteriorly in an ampullofugal (inhibitory) direction, creating a (weak) slow phase to the right and a fast phase to the left (left-beating nystagmus toward the healthy ear) https://collections.lib.utah.edu/ark:/87278/s68h2wk9. (Video created with the assistance of Dr. Ari Shemesh)