Primary Position Upbeat Nystagmus

Two patients with upbeat nystagmus in the primary position of gaze were studied neuro-otologically. The nystagmus appeared with oscillopsia and body imbalance in gait and standing. These symptoms appeared during malnutrition caused by the loss of appetite. One patient was alcoholic and the other had a psychiatric disorder. Nutritional encephalopathy was diagnosed in both patients. 1) Upbeat nystagmus was observed during forward, downward, right and left gaze. It did not behave in accordance with Alexander's law. Pursuit eye movement in the upward direction was saccadic, and the velocity of saccadic eye movement in the downward direction decreased. Vertical optokinetic nystagmus could not be elicited. Disturbance of horizontal eye movements was observed in pursuit eye movement and optokinetic nystagmus. 2) The position and velocity of the head and eyes during vertical head oscillation with fixation on an earth-fixed visual target were recorded with a microcomputer and a specially designed program. The velocity of upward eye movements was faster than that of downward eye movements, suggesting a disturbance of the integration mechanism from position signal to velocity signal in visual and vestibular pursuit eye movement. We concluded that a disturbance of the neural integrator in the prepositus hypoglossi nuclei was probably responsible for upbeat nystagmus in these patients.