A 16-year-old boy with rotatory positional vertigo and nausea, particularly when lying down, visited our clinic. Initially, we observed vertical/torsional (downward/leftward) nystagmus in the supine position, and it did not diminish. In the sitting position, nystagmus was not provoked. Neurological examinations were normal. We speculated that persistent torsional down-beating nystagmus was caused by the light cupula of the posterior semicircular canal. This case provides novel insights into the light cupula pathophysiology.
In the head-hanging position, positional down-beating nystagmus (p-DBN) generally occurs in patients with a cerebellar nodulus lesion [
A 16-year-old boy with rotatory positional vertigo and nausea particularly when lying down and at the time of rising visited our clinic on the next day of onset. He denied any hearing loss, tinnitus, headache, or facial neurological symptoms. Past medical, surgical, and family history and head trauma were unremarkable. There was no dysdiadochokinesis, dysmetria, or tremors. Gait was not ataxic, and there was no spontaneous or gaze-evoked nystagmus. Pure tone audiogram, neurological, and eye movement examinations, including the eye-tracking test, saccades, and drum optokinetic nystagmus test, were normal. Brain magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) findings were normal. The positional and positioning nystagmus test, including the supine head roll and bilateral Dix-Hallpike tests, was recorded using an infrared charge-coupled device camera. The supine head roll test revealed DBN with the torsional component toward the left without latency in straight and right supine positions (Figure
Video-oculographic recording of torsional down-beating nystagmus in the supine position in the head roll test. The vertical component is observed to be down-beating (slow phase velocity 16.5°/s, 84 beats/min) on the vertical recording. The torsional component is observed as a horizontal component beating toward the left on the horizontal recording. Video-oculography was performed using the public domain software ImageJ and a Windows computer [
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We speculated that persistent torsional DBN occurred because of the light cupula of the right posterior semicircular canal in the patient.
Persistent geotropic direction-changing positional nystagmus with the neutral position when turning the head to either side in the supine position reportedly occurred because of the light cupula of the horizontal semicircular canal [
In the light cupula of the posterior semicircular canal, persistent DBN with the torsional component toward the unaffected ear was observed in the affected ear-down position in the supine head roll test, because this position causes ampullopetal deflection of the cupula according to Ewald’s third law (Figure
A light cupula of the right posterior semicircular canal. Arrows indicate the deflection of the cupula. U: utricle.
Supine position
Sitting position
Several studies have reported that nystagmus of A-BPPV had down-beating component with or without a torsional component in the head-hanging position on the Dix-Hallpike test [
Vannucchi et al. reported that torsional DBN in the head-hanging position in the Dix-Hallpike test also occurred because of a rare variant canalolithiasis of the posterior semicircular canal [
P-DBN in the head-hanging position, with or without slight positional vertigo, is indicative of a cerebellar nodulus lesion and may be caused by multiple sclerosis, ischemia, intoxication, craniocervical malformation, or cerebellar degeneration [
In conclusion, we speculated that persistent torsional DBN in our patient was due to the light cupula of the posterior semicircular canal. We determined that the condition of the light cupula probably occurred not only in the horizontal but also in the posterior semicircular canal. These findings prove useful for elucidating the light cupula pathophysiology.
The authors declare that they have no competing interests.