Treatment of the gravity dependence of downbeat nystagmus with 3,4-diaminopyridine.

The authors examined the effect of 3,4-diaminopyridine (DAP) on the gravity-dependent (GD) vertical ocular drift component of downbeat nystagmus in 11 patients with idiopathic cerebellar ataxia. With the head tilted downward (45 degrees ), DAP reduced slow phase velocity (SPV) in 7 of 11 patients by 36%. Its efficacy correlated with the GD modulation. DAP minimizes the gravity-independent velocity bias and may improve deficient inhibitory cerebellar control on overacting otolith-ocular reflexes.