非注視下で周期性方向交代性眼振を認めた内耳道に限局した聴神経腫瘍例

抄録

Periodic alternating nystagmus (PAN) may be related to vestibulocerebellar system disease, occur with a loss of vision, and be congenital in origin. Acquired PAN has been reported in association with a variety of conditions, many of which involve the cerebellum. However, our case with PAN was a patient with an acoustic tumor localized in the internal auditory canal.
This case was a 28-year-old female. She underwent an initial medical examination in June 2004. Her chief complaint was hearing impairment. However, in all test, we could not identify any audiogram abnormality. In September of the same year, she became dizzy, and had a vertigo attack on the 15th November. We thus admitted to hospital. During this hospitalization, we identified PAN in the equilibrium test.
Waespe et al. have reported that experimental ablation of the nodulus and uvula of the cerebellum in monkeys causes PAN; baclofen abolishes this nystagmus. Pharmacological evidence suggests that the nodulus and uvula maintain inhibitory control vestibular responses using GABA. Thus, the GABA agonist baclofen is able to abolish PAN due to experimental or clinical lesions of the nodulus and uvula.
Leigh et al. have presented a hypothetical explanation for PAN based on instability in central vestibular-optokinetic pathways. They have suggested that normal vestibular adaptation mechanisms act to reverse the direction of PAN.
In this case, the characteristic pattern of peripheral nystagmus was indicated, PAN was abolished without baclofen, and MRI imaging showed that the acoustic tumor was localized in the internal auditory canal. Furthermore, findings of cerebellar disorder were not seen. So, our case's PAN seems to support the latter opinion.