The “light cupula” phenomenon masquerading in congenital nystagmus

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Abstract Objective/Hypothesis: Congenital nystagmus alone does not cause vertigo or dizziness, but we often encounter patients with this condition who complain of dizziness or vertigo. These patients also show positional nystagmus under an infrared camera (opened in the dark). Among them, we found a patient who had persistent direction changing positional nystagmus (DCPN) with two neutral points. This type of nystagmus is thought to be due to “light or heavy cupula” of the affected ear’s lateral semi-circular canal (SCC). The neutral point is deviated to the right or left from the supine position (first neutral point), and the deviated side is the affected side. If “light or heavy cupula” reflects the pathological condition of the endolymph in the affected ear lateral SCC, the side of the neutral point is thought to show the side of vestibular disorder. Case Report: The patient was a 51-year-old woman who complained of sudden onset of vertigo and hearing loss in the left ear. After admission therapy, hearing loss improved, but nystagmus did not disappear. She was diagnosed as having congenital nystagmus by typical electronystagmography. After this, she suffered vertiginous episodes and her left hearing level fluctuated and deteriorated. She was diagnosed with Meniere's disease. Simultaneously, she also showed persistent DCPN with two neutral points (“light cupula” type was observed eight times and “heavy cupula” type was twice.), whose first neutral point’s side changed at each time. Finally, she continued showing “light cupula” type persistent DCPN with two neutral points. Conclusion: The clinical characteristics of our patient suggested that bilateral latent vestibular disorder can occur in patients with Meniere's disease suffering from unilateral hearing impairment behind the congenital nystagmus. Persistent DCPN including “light cupula” can be explained by changes of the specific gravity of the surrounding endolymph in the affected ear.