Horizontal nystagmus is gravity-dependent in patients with vestibular neuritis

Horizontal nystagmus can be observed in the acute stage of vestibular neuritis, Although the direction of the nystagmus is gravity independent, its intensity can be influenced by gravity. In this study, we compared the slow phase velocity (SPV) of horizontal nystagmus in different head positions in patients with vestibular neuritis to analyze the static effects of gravity on horizontal nystagmus.

The study enrolled 22 vestibular neuritis patients with spontaneous horizontal nystagmus (9 men, 13 women; median age 40 years). The deficits were right-sided in 9 patients and left-sided in 13. The nystagmus was recorded in the sitting, supine, right and left ear down positions. The intensity of spontaneous nystagmus in the sitting versus while supine position, and SPV in affected ear down (AED), healthy ear down (HED), and supine positions were compared. The position-induced nystagmus was calculated to quantify the effect of head positions on nystagmus.

The nystagmus intensity in the supine position had no statistic difference than when sitting, with a median value of 6.3°/s and 5.6°/s, respectively(P = 0.355). SPV in AED had a median value of 7.8°/s, which was greater than when supine (P = 0.008) and HED (4.8°/s) (P < 0.001). Position-induced nystagmus in left and right ear-down positions were 1.4°/s and -1.4°/s respectively, which were significantly correlated (Spearman's ρ = -0.848, P < 0.001).

The nystagmus intensity in vestibular neuritis is gravity dependent; it's greater in AED than in supine and HED, and the effect of head position on nystagmus was nearly symmetrical in left and right ear-down positions.