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Primary position upbeat nystagmus has been associated clinically with lesions of the midbrain,1 cerebellar vermis,2-5 brachium conjunctivum,6 and lower brain stem near the inferior olive.7-9 However, only the latter two lesions have been confirmed pathologically.6-8 Even in these studies, the precise localization remains unclear. We report a case of primary position upbeat nystagmus with a discrete vascular lesion that involved the hypoglossal nucleus and and adjacent structures.
REPORT OF A CASE
A 39-year-old woman was admitted seven days after a sudden onset of dysarthria and vertical oscillopsia. Results of an examination showed primary position upbeat nystagmus that persisted in all directions of gaze. No other oculomotor abnormalities were noticed. The tongue deviated to the right; fasciculation and slight atrophy were seen on the right side of the tongue with simultaneous palatal weakness (Fig 1). No other abnormal signs were observed.Normal laboratory studies included complete
Kato I, Nakamura T, Watanabe J, Harada K, Aoyagi M, Katagiri T. Primary Position Upbeat Nystagmus: Localizing Value. Arch Neurol. 1985;42(8):819–821. doi:10.1001/archneur.1985.04210090087024
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