A 20-year-old man with bilateral medial medullary infarction showed transition of bowtie and upbeat nystagmus intohemi-seesaw nystagmus. Follow-up MRI revealed near complete resolution of the right medullary lesion. This transitionof nystagmus suggests that the upbeat nystagmus was generated by bilateral lesions in the ascending pathways fromboth anterior semicircular canals (SCC), and that the hemi-seesaw nystagmus was caused by damage to the pathwayfrom the left anterior SCC.
