Elsevier

Auris Nasus Larynx

Volume 38, Issue 1, February 2011, Pages 46-51
Auris Nasus Larynx

Two types of direction-changing positional nystagmus with neutral points

https://doi.org/10.1016/j.anl.2010.07.004Get rights and content

Abstract

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.

Introduction

Static direction-changing positional nystagmus (DCPN), which disappears at about 20–30° yaw head rotation from the supine position, is classified as “heavy” or “light” cupula type DCPN [1]. Heavy cupula type DCPN is thought to be caused by detached otoconia rather than by the specific gravity of the endolymph, though a “heavy cupula” may be caused by “cupulolithiasis” or “buoyancy” in the horizontal canal. On the contrary, light cupula type DCPN is strongly thought to be caused by increased specific gravity of the endolymph [1]. Clarification seems to be needed for the following issues: (1) What clinical differences exist between the two types? (2) How large is the angle (θ) between the supine position and the neutral point exactly? and (3) How is vestibular function and which ear is affected? Examination of these issues may lead to a better understanding of the pathomechanisms of the two types of DCPN with neutral points.

Section snippets

Patients and methods

Sixteen patients who exhibited DCPN with neutral points were examined at the National Hospital Organization Chiba Medical Center and Tokyo Metropolitan Komagome Hospital between 2002 and 2007. An infrared camera (installed in goggles) (IRN-1, J. Morita MFG. Corp., Kyoto, Japan) or Frenzel glasses were used to distinguish heavy from light cupula type DCPN. Heavy cupula type DCPN shows nystagmus beating toward the neutral points (Fig. 1A), while light cupula type DCPN shows nystagmus beating away

Results

Heavy cupula type DCPN was found in 9 patients and light cupula type DCPN was detected in 7 patients. The male to female ratio in heavy cupula type DCPN was 4:5 and the ratio of right to left side deviation was 7:2 (Table 1). The male to female ratio and the ratio of right to left side deviation in light cupula type DCPN was 2:5 (Table 1). The angle (θ) between the supine position and first neutral point was 26.5 ± 11.6° (n = 15): heavy type 24.5 ± 8.7° (n = 8) and light type 28.7 ± 14.5° (n = 7), showing

Discussion

We encountered patients whose static DCPN was 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. As shown in Fig. 1, at the neutral points the cupula of the horizontal semicircular canal of the right ear is positioned vertical to the gravitational plane, and no deflection of the cupula occurs. Heavy cupula type DCPN exhibits nystagmus beating

Conclusions

DCPN with neutral points was classified into heavy cupula type and light cupula type. Heavy cupula type may occur due to otoconia and light cupula type may occur due to an increased density or viscosity of the surrounding endolymph. Anatomically, the angle between the supine position and neutral point is considered to be the angle between the cupula and the gravity vector on the plane of the affected lateral semicircular canal. The concurrence of direction between the gravitational vector and

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