Two types of direction-changing positional nystagmus with neutral points

Objectives

We encountered patients who had static direction-changing positional nystagmus (DCPN) canceled at about 20-30° yaw head rotation from the supine position. This nystagmus was also canceled when the head was rotated 180° from this position. We termed these head positions neutral points. The positional nystagmus observed (except at the neutral points) was thought to occur due to a “heavy cupula” or “light cupula”. The purpose of this study was to examine DCPN with neutral points as well as the pathomechanism of this condition.

Methods

Retrospective case review of patients attending two hospitals. Sixteen patients who exhibited DCPN with neutral points were examined using an infrared camera (installed in goggles). Using this system, the vestibulo-ocular reflex (VOR) was recorded, and VOR gain was obtained. Vestibular function and the affected side were determined. In addition, the angle between the supine position and neutral point was measured in each patient. We also examined other positional nystagmus occurring at other times.

Results

In the heavy cupula type group, we noted positional nystagmus for which repositioning maneuvers were successful, whereas, in the light cupula type group, repositioning maneuvers were not effective. The angle between supine position and neutral point was 26.5 ± 11.6°.

Conclusions

Heavy cupula type may occur as a result of otoconia while light cupula type may be due to the specific gravity of the endolymph. The VOR gain and side of the benign paroxysmal positional vertigo (BPPV) observed suggested that the affected side was that to which the neutral point was deviated.     

Benign paroxysmal positional vertigo showing sequential translations of four types of nystagmus

Objective

We report a case of benign paroxysmal positional vertigo (BPPV) showing sequential translation of four types of nystagmus and discuss its pathophysiology.

Methods

The case was 65-year-old female. We analyzed her nystagmus three-dimensionally.

Results

At the first visit, she showed vertical-torsio nystagmus of the posterior canal type of BPPV (P-BPPV) and subsequently showed recently reported geotropic nystagmus with a long time constant. Two weeks later, she showed apogeotropic nystagmus of the horizontal canal type of BPPV (AH-BPPV) and subsequently a geotropic nystagmus with a short time constant of the horizontal canal type of BPPV (GH-BPPV).

Conclusions

Three kind of nystagmus, namely P-BPPV, AH-BPPV and GH-BPPV can be explained by the otoconial debris hypothesis of the same ear. Finally, the recently reported geotropic nystagmus with a long time constant may be explained by a reversible lesion such as the denatured cupula or utricular imbalance of the same ear.     

Transdermally administered scopolamine vs. dimenhydrinate. II. Effect on different types of nystagmus

The effects of transdermally administered scopolamine (TTS-scopolamine) (release rate 5 micrograms/h, one and two patches) and dimenhydrinate (100 mg) on caloric, angular acceleration induced and optokinetic nystagmus were examined in 16 volunteers in a randomized double-blind study. All drugs induced a statistically significant decrease in maximum velocity of caloric nystagmus, as compared with placebo. In the rotatory test, two TTS-scopolamine and dimenhydrinate reduced the vestibular gain significantly. No changes were observed in time constant. In the optokinetic test, all drugs tended to reduce the responses, but a statistically significant reduction was found only after two TTS-scopolamine. The results indicate that the drugs effective against motion sickness reduce the nystagmic response, which at least partly explains the mode of action of the drugs. The target organ of the drugs is presumably the vestibular nucleus, where vestibular and visual impulses are integrated to ensure optimal gain for vestibular orientation reflexes.     

Effect of body positions in human optokinetic nystagmus and optokinetic after nystagmus

We determined whether whole body tilt would shift the axis of optokinetic nystagmus (OKN) and optokinetic-after nystagmus (OKAN) induced by full-field rotation at 35 degrees/sec. Fifteen normal people were positioned upright or tilted 30 degrees, 60 degrees or 90 degrees to both sides. Stripes of 5 degrees were projected on a 10-foot dome around the subject's yaw axis. Each trial lasted 45 sec. The lights were then extinguished, and the subject remained in darkness for 30 sec, while after nystagmus (OKAN) was recorded. Horizontal and vertical eye movements were recorded by video-oculography at 60 Hz. Eye position and velocity data were stored on optic disk cartridge by use of the data acquisition system. A. OKAN: For the subject in the upright position, the OKN velocity vector was aligned with both gravity and the subject's yaw axis with two minor exceptions. When the subject was tilted, a vertical OKN component (VOKN) appeared in a majority of subjects. For all 15 subjects, the mean angle of the OKN velocity vector regravity (Vectorg) was 22.6 +/- 7.2 degrees at 30 degrees tilted position. The Vectorg were 48.5 +/- 10.3 degrees at 60 degrees tilted position, and 76.4 +/- 12.6 degrees at 90 degrees tilted position. This represented shifts of the OKN velocity vector from the body axis of 7.4 degrees, 11.5 degrees and 13.6 degrees, respectively. The horizontal OKN (HOKN) gain remained unchanged in different positions. B. OKAN: The duration of HOKAN and initial slow phase velocity (SPV) of HOKAN decreased as the body position increased from upright to 30 degrees, 60 degrees and 90 degrees tilted position, respectively. The incidence and initial SPV of VOKAN and Re-Body did not change as the body position increased from upright to 30 degrees, 60 degrees and 90 degrees tilted position, respectively. Thus, VOKN was observed during HOKN as subjects were tilted and tended to vector to gravity, but VOKAN was not always observed during horizontal OKAN when subjects were tilted.