A Case Report on the Apogeotropic Direction Changing Type of Positional Nystagmus Following Acoustic Trauma

A 56-year-old man complained of a hearing loss and tinnitus in his right ear after short intense exposure to a high level of sound. Although he had no complaints of vertigo or dizziness, his neuro-otological examination revealed apogeotropic direction changing type of positional nystagmus. An audiogram showed right high-frequency sensorineural hearing loss. An eye tracking test (ETT) and an optokinetic nystagmus (OKN) test showed no abnormalities. A caloric test showed normal responses in both ear sides. One week after the exposure to a high level of sound, the positional nystagmus completely disappeared. Apogeotropic direction changing type of positional nystagmus is generally considered to be a phenomenon observed in patients with central vestibular lesion. However, physical examination and laboratory tests of this patient suggested that he suffered from only a peripheral vestibular impairment. From these results, apogeotropic direction changing type of positional nystagmus observed in this patient resulted from an impair-ment of the peripheral vestibular system.