Positional Nystagmus Showing Neutral Points

Abstract

We encountered patients who had their static direction-changing positional nystagmus 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 call these head positions neutral points. At the neutral points, the cupula of the horizontal semicircular canal of the affected ear is positioned vertical to the gravitational plane and no deflection of the cupula occurs. The positional nystagmus observed (except the neutral points) was thought to occur due to a ‘heavy cupula’ or ‘light cupula’, which may be determined by the specific gravity of its endolymph.

“Light cupula” involving all three semicircular canals: A frequently misdiagnosed disorder

“…The concept of light cupula has been recently introduced for the diagnosis of patients with positional vertigo and persistent DCPN [1][2][3][4][5][6]. Positional nystagmus with the following characteristics is observed in patients with light cupula: (1) persistent geotropic DCPN without latency on the supine head-roll test, (2) the presence of a null plane at which geotropic nystagmus ceases on slight turning of the patient's head (15-40°) to the affected side, (3) horizontal nystagmus towards the affected side at the bowing (90°n ose-down) position, (4) horizontal nystagmus towards the healthy side when lying down (the supine position), and (5) spontaneous nystagmus towards the healthy side in the sitting position without neck flexion or extension [1][2][3][4][5][6].…”

“…Positional nystagmus with the following characteristics is observed in patients with light cupula: (1) persistent geotropic DCPN without latency on the supine head-roll test, (2) the presence of a null plane at which geotropic nystagmus ceases on slight turning of the patient's head (15-40°) to the affected side, (3) horizontal nystagmus towards the affected side at the bowing (90°n ose-down) position, (4) horizontal nystagmus towards the healthy side when lying down (the supine position), and (5) spontaneous nystagmus towards the healthy side in the sitting position without neck flexion or extension [1][2][3][4][5][6]. Of these characteristics, persistent geotropic DCPN without latency on the supine head-roll test is the most important diagnostic criterion for the diagnosis of the light cupula [1].…”

“…Of these characteristics, persistent geotropic DCPN without latency on the supine head-roll test is the most important diagnostic criterion for the diagnosis of the light cupula [1]. Because the theory of light cupula in the clinical field has been only recently introduced [6] and evidence supporting the theory is indirect, the diagnosis of light cupula might have been disregarded by many clinicians. The clinical practice guidelines for BPPV also do not consider light cupula a differential diagnosis in patients with positional vertigo [9].…”

“…The geotropic DCPN of LSCC canalolithiasis is transient, has latency of a few seconds, and is either weakened or lost after repetitive examination (fatigability). On the other hand, the nystagmus observed in the light cupula, which also exhibits geotropic DCPN on the head-roll test, is persistent without latency or fatigability [1][2][3][4][5][6]. The percentage of patients with geotropic DCPN due to the light cupula has been reported to be as high as 14.2% [1]; however, this disease entity has been somewhat underestimated in the differential diagnosis of positional vertigo.…”

The Density Difference of Cupula and Endolymph Changes the Mechanics of Semicircular Canals

“…cupulolithiasis) or local inflammatory processes; (5) daily fluxes of endolymph composition (Borelli et al 2003). There are some, although limited, electrophysiological data suggesting a canal sensitivity to linear acceleration and to the orientation of the canals relative to gravity (Ledoux 1949;Lowenstein and Compton 1978;Hiruma and Numata 2004). The effects of positional geotropic nystagmus were also explained by the difference of specific weights of cupula and surrounding endolymph (Money and Myles 1974).…”