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Spontaneous nystagmus in dorsolateral medullary infarction indicates vestibular semicircular canal imbalance

Background: Spontaneous nystagmus caused by dorsolateral medullary infarction may be of vestibular origin. Objectives: To test if imbalance of the central pathways of the semicircular canals contributes to spontaneous nystagmus in dorsolateral medullary syndrome. Methods: We examined four patients with dorsolateral medullary syndrome and recorded spontaneous nystagmus binocularly at gaze straight ahead with the three-dimensional search coil technique. The median slow phase velocity of the nystagmus was analysed in the light and in the dark, and the normalised velocity axes were compared with the rotation axes as predicted from anatomical data of the semicircular canal. Results: The slow phase rotation axes of all patients aligned best with the rotation axes resulting from stimulation of the contralesional posterior and horizontal semicircular canals. This alignment cannot be explained by pure otolith imbalance. Conclusion: We propose that vestibular imbalance caused by an ipsilesional lesion of the central semicircular canal pathways of the horizontal and anterior semicircular canals largely accounts for spontaneous nystagmus in dorsolateral medullary syndrome.