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

Though benign paroxysmal positional vertigo (BPPV) is the most common vestibular disorder causing positional vertigo, 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 was introduced, which accounts for some of positional vertigo. Under a normal condition in which the specific gravity of the cupula is same as that of the surrounding endolymph, semicircular canals (SCCs) are not influenced by the gravity. The light cupula, which indicates cupula with lower specific gravity than the surrounding endolymph, is characterized by persistent geotropic direction-changing positional nystagmus (DCPN) without latency on the supine head-roll test and the presence of a null plane. Unless the duration and pattern of positional nystagmus are carefully examined, the light cupula can be misdiagnosed as other types of BPPV. We present a patient with light cupula on the right side who reported recurrent episodes of positional vertigo and had been diagnosed as BPPV with multiple canal involvement (posterior and lateral SCCs) on the opposite side. In this study, we present the mechanism of typical positional nystagmus patterns in patients with light cupula involving all of the unilateral SCCs, and discuss the possible causes of misdiagnosis of the light cupula.