Persistent geotropic direction‐changing positional nystagmus with a null plane: The light cupula

Abstract

The patients with light cupula show persistent geotropic DCPN without latency. Affected side(s) can be determined by the direction and intensity of the characteristic positional nystagmus and the side of the null plane. The pathophysiology and treatment of light cupula still remain to be elucidated.

“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].…”

“…1E), and a diagnosis of light cupula on the right side was made by Ewald's second law [1]. A null plane at which the geotropic nystagmus disappeared could be identified when the patient's head was slightly (about 35°) turned to the right in the supine position, which indicated that the cupula of the right LSCC is aligned with the direction of the gravity vector [1]. Then, the Dix-Hallpike test was performed with the patient in the sitting position.…”

“…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.…”

“…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. In fact, differential diagnosis between the light cupula and the canalolithiasis type of LSCC BPPV is difficult unless the latency and persistency of the nystagmus are carefully examined on the supine head-roll test.…”

“…However, patients with typical positional vertigo in which the findings of positional nystagmus do not meet the diagnostic criteria for BPPV are often encountered in the clinic. Recently a concept of the light cupula has been introduced, which accounts for some of positional vertigo [1][2][3][4][5]. The light cupula indicates the cupula with lower specific gravity than the surrounding endolymph of which specific gravity is same as that of the cupula under normal condition.…”