Case Report: A light cupula phenomenon involving all three semicircular canals?

This is the authors' abstract. We don't add key points for this paper.

The light cupula phenomenon is an uncommon vestibular disorder characterized by persistent, direction-changing positional nystagmus with rapid onset without fatigue. While often reported in the horizontal semicircular canal, involvement of all three semicircular canals is remarkably rare. We present a case of a 55-year-old male with acute-onset vertigo and distinctive geotropic horizontal nystagmus in the supine position accompanied by a vertical downbeat component in the upright position, suggesting simultaneous cupula activation in all three semicircular canals of a single vestibular apparatus. Neurological and imaging evaluations ruled out central causes. In accordance with clinical and radiological findings, the light cupula phenomenon caused by heavier endolymph appeared to best explain our patient's findings. This case highlights the diagnostic complexity of light cupula syndrome, particularly regarding its vertical canal manifestations, which remain poorly understood. Future comprehensive research of the anatomy and pathophysiology of the light cupula phenomenon across the whole vestibular apparatus is needed to improve clinical recognition and management.