Superior Cerebellar Peduncle Demyelination Causing Geotropic Central Positional Nystagmus

While the presence of spontaneous nystagmus in multiple sclerosis (MS) patients frequently constitutes a sign of disease relapse, the occurrence of positional nystagmus is more often due to a non-MS cause (e.g., benign paroxysmal positioning vertigo (BPPV)). Rarely, a strategic infratentorial lesion can cause central positional/positioning nystagmus (CPPN) and mimic BPPV. Apogeotropic and downbeat CPPN constitute the commonest forms. We describe a MS patient with geotropic CPPN caused by a superior cerebellar peduncle (SCP) demyelinating plaque.