[Light cupulopathy: persistent direction changing positional nystagmus with a null plane].

Objective: The purpose of this study was to report two cases of light cupulopathy, and describe the characteristics of these cases and analysis the possible physiopathological mechanisms. Methods: The histories, clinical features, characteristics of nystagmus, and vestibular function, as well as audiologic results of the two patients with light cupula were analyzed. Results: The two patients showed persistent geotropic direction changing positional nystagmus(DCPN)in the supine head roll tests. The null plane was present when the head was turn slightly towards affected side. Canalith repositioning maneuver was not effective. A mild sensorineural hearing loss was found on the involved ear in one patient but not in the other. The vestibular functions of two patients were abnormal. Conclusions: The characteristics of nystagmus with light cupulopathy are persistent geotropic DCPN with a null plane. The clinical features are similar with the horizontal semicircular canal canalolithasis. Canalith repositioning maneuver is not recommended for its ineffectiveness.