Abstract
We often encounter clinical cases with nystagmus or abnormal eye movements that are suspected to be associated with central vertigo. However, imaging techniques such as magnetic resonance imaging (MRI) may not always yield abnormal findings for such cases. For 2 patients who were suspected as having central vertigo on the basis of oculomotor testing but had normal MRI findings, we identified the lesion site using the results of neuro-otological tests. (1) Since direction-changing positional nystagmus was observed, with inhibited optokinetic nystagmus or saccadic pursuit, we suspected cerebellar or brain stem lesions. (2) Caloric testing yielded a normal response. Hence, the vestibular nucleus, abducens nucleus, oculomotor nerve nucleus, and medial longitudinal fasciculus were considered to be lesion-free. Visual suppression was also normal; this allowed us to rule out the pons, cerebellar flocculus, and nodulus as lesion sites. Moreover, preserved saccadic speed indicated no damage to the pons or midbrain. (3) Because hypermetria was observed during the saccade, we suspected damage to the cerebellar fastigial nucleus. Further, drift to the median during the saccade and gaze-evoked nystagmus were observed, suggesting a lesion in the nucleus prepositus hypoglossi, which is a neural integrator. Both our patients showed poor laterality; therefore, they were thought to have a degenerative disease. From the above-mentioned findings, we propose that MRI cannot reveal any abnormalities during the very early stages of spinocerebellar degeneration.
