Down beating nystagmus: magnetic resonance imaging and neuro-otological findings.

Twenty-four patients with down beating nystagmus (DBN) underwent magnetic resonance imaging (MRI) of the head. MRI provided diagnostic images in Arnold-Chiari malformation (6 cases), cerebellar atrophy (6 cases), 1 case with a prepontine-medullary epidermoid tumour and was helpful in the diagnosis of 2 patients with multiple sclerosis and 1 with a ponto-cerebellar infarct. Multiple cerebral hemisphere lesions were found in 6 patients (5 of them over 60 years of age) in whom no diagnosis was made. All cases of DBN, plus 3 additional patients with Arnold-Chiari malformation and other types of nystagmus, were neuro-otologically assessed. Sensitivity of the nystagmus to head tilt with respect to the gravity vector had no localizing value. Impaired horizontal vestibulo-ocular reflex suppression occurred more frequently in those patients with abnormal posterior fossa MRI. Pure torsional nystagmus, and DBN with a strong torsional component, in patients with Arnold-Chiari malformation was associated with syringomyelia. Magnetic resonance is the imaging method of choice for investigating patients with DBN.