Downbeat nystagmus in association with the dorsal midbrain syndrome: proposed mechanisms, literature review, and case series

In five patients with DBN and dorsal midbrain syndrome, aqueductal stenosis or compression with upgaze paresis were unifying features. Potential mechanisms for DBN include involvement of the interstitial nucleus of Cajal, disruption of descending midbrain projections to paramedian tracts, or unstable cerebellar outflow, but clinical and experimental evidence makes these explanations less compelling. Converging evidence from our series, prior reports, and non-human primate studies suggests bilateral posterior commissural dysfunction related to aqueductal pathology as the most plausible mechanism for DBN with the dorsal midbrain syndrome.