Multiple sclerosis as a cause of the acute vestibular syndrome.

Multiple sclerosis (MS) causes dizziness and vertigo. Reports suggest responsible lesions are often in the intra-pontine 8th nerve fascicle. We sought to determine frequency and clinical features of demyelinating acute vestibular syndrome (AVS). This is a prospective observational study (1999-2011). Consecutive AVS patients (vertigo, nystagmus, nausea/vomiting, head-motion intolerance, unsteady gait) with a risk for central localization underwent structured bedside examination and neuroimaging. When applicable, we identified MS based on clinical, imaging, and laboratory features. Of 170 AVS presentations, 4% (n = 7) were due to demyelinating disease. Five had an acute MS plaque likely responsible for the clinical syndrome. Lesion location varied-1 medulla; 1 inferior cerebellar peduncle; 1 middle cerebellar peduncle; 1 posterior pontine tegmentum; 1 in the intrapontine 8th nerve fascicle; 1 superior cerebellar peduncle; 1 midbrain. Only two had a lesion in or near the intra-pontine 8th nerve fascicle. Three were first presentations (i.e., clinically isolated demyelinating syndrome), while the others were known MS. All had central oculomotor signs. In two patients, the only central sign was a normal horizontal head impulse test (h-HIT) of vestibular function. All patients improved with steroid therapy. Demyelinating disease was an uncommon cause of AVS in our series. Symptomatic lesions were not restricted to the 8th nerve fascicle. Five patients had relatively obvious oculomotor signs, making differentiation from vestibular neuritis straightforward. Two patients had unidirectional, horizontal nystagmus that followed Alexander's law and was suppressed with fixation (true pseudoneuritis). The presence of a normal h-HIT in these suggested central localization.