title: Periodic alternating nystagmus during caloric stimulation.
abstract: Periodic alternating nystagmus (PAN) is a form of horizontal jerk nystagmus characterized by periodic reversals in direction. We report a case who exhibited transient PAN induced by caloric stimulation. The patient was a 75-year-old male. He had experienced floating sensation in January 2010. Eight months later, he was referred to our university hospital. Gaze nystagmus and positional tests revealed no nystagmus. Only weak right-beating horizontal nystagmus was observed during left Dix-Hallpike maneuver. Electronystagmography showed normal saccadic and smooth pursuit eye movements. The optokinetic nystagmus pattern test was also bilaterally normal. However, during the caloric stimulation to the right ear, at 166 s from the start of irrigation, the direction of nystagmus alternated from leftward to rightward, and thereafter this reversal of direction repeated 15 times. Magnetic resonance imaging showed no significant lesion except for chronic ischemia in the brain. The patient probably had some kind of latent lesion of impaired velocity storage and exhibited transient PAN induced by caloric stimulation. Caloric stimulation is useful and simple examination to disclose latent eye movement disorders of which velocity storage mechanism is impaired.
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Kyoto Prefectural University of Medicine, Kyoto, Japan. Electronic address: taki@koto.kpu-m.ac.jp.
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Taki
authors.affiliation: Department of Otolaryngology, Kyoto Prefectural Yosanoumi Hospital, Yosa, Kyoto, Japan.
authors.forename: Tatsuhisa
authors.initials: T
authors.lastname: Hasegawa
authors.affiliation: Department of Otolaryngology, Maizuru Medical Center, Maizuru, Kyoto, Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Adachi
authors.affiliation: Department of Otolaryngology, Omihachiman Community Medical Center, Omihachiman, Shiga, Japan.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Fujita
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Sakaguchi
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Hisa
mesh_terms: D000368:Aged; D001921:Brain / Q000473:pathology*; D002150:Caloric Tests; D004584:Electronystagmography; D006801:Humans; D002534:Hypoxia, Brain / Q000150:complications / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging; D008297:Male; D009759:Nystagmus, Pathologic / Q000150:complications / Q000175:diagnosis*
keywords: Caloric stimulation; Periodic alternating nystagmus; Velocity storage