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Primary position upbeat nystagmus
Ivan Adamec1, Tereza Gabelić, Magdalena Krbot
1Department of Neurology, Zagreb School of Medicine and University Hospital Center, Referral Center for Demyelinating Diseases of the Central Nervous System, Kišpatićeva 12, Zagreb HR-10000, Croatia.
Abstract:
Primary position upbeat nystagmus is a rare clinical finding. We report a patient with clinically isolated syndrome suggestive of multiple sclerosis who presented with primary position upbeat nystagmus. MRI revealed a demyelinating lesion in the lower medulla, which affected the nucleus intercalatus; this type of lesion inhibits the flocculovestibular inhibitory pathway, thereby causing upbeat nystagmus. Nystagmus still persisted after pulsed corticosteroid therapy. This could be due to a loss of central adaptation of the vestibulo-ocular system in our patient, because of more diffuse brainstem damage, shown on vestibular-evoked myogenic potentials as delayed latencies on both sternocleidomastoid muscles and a conduction block for the left extraocular muscles.
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