[Clinical evaluation of primary position downbeat nystagmus].

PURPOSE: Primary position downbeat nystagmus is a vertical nystagmus with a rapid phase downwards presenting in any gaze. We evaluated causative lesions, etiology, and incidence by age groups.

MATERIALS AND

METHODS

Twenty-five patients with primary position downbeat nystagmus were enrolled in this study. Their causative lesions, etiology, and frequency by age group were investigated. We divided the patients into 3 groups depending on age; under 30, from 30 to 60, and over 60 years.

RESULT: Cerebrovascular disorder was diagnosed in 5 patients. Four patients had cerebellar degeneration. Three patients had multiple sclerosis or Arnold-Chiari malformation. Two patients had cerebellar tumor. In the young group under 30, etiology was mainly cerebellar tumor or multiple sclerosis. Especially cerebellar tumor was limited to this group. In the middle age group, there was no distinctive tendency. In the older group over 60 years, cerebrovascular disorder was predominant. In 10 patients with intracranial lesions, the foci were located in the cerebellum, pons, or medulla oblongata.

CONCLUSION

The causes of primary position down beat nystagmus tended to be age-dependent. The locations of causative lesions were the cerebellum and the inferior brain stem.