A 68-year-old woman visited a neighbor hospital with a 2-month history of floating dizziness. Brain MRI revealed a large tumor occupying the entire left cerebellar hemisphere, and the patient was transferred to the department of neurosurgery at our hospital. The patient was diagnosed as having a diffuse large B-cell lymphoma primarily originating from the cerebellum by stereotactic needle biopsy study and positive results of immunohistochemistry for the surface markers CD 19 and CD 20. The patient recovered completely after 4 cycles of combined chemotherapy with high-dose methotrexate and Ara-C. However, she visited our department again complaining of persistent floating dizziness. Neurological examination revealed no significant findings other than the upward and leftward gaze-evoked nystagmus (GEN). ENG showed GEN during upward and leftward gaze in the light. Both horizontal and vertical pursuits were disturbed and the saccadic pursuit was marked. The horizontal optokinetic nystagmus (OKN) was poorly induced, while caloric nystagmus was well induced by cold water bilaterally. GEN is attributed to a deficit in the velocity-to-position integrator, suggestive of brain stem or cerebellar lesions. GEN is also known to be closely correlated with deficits of smooth pursuit eye movements and slow phase of OKN, as in our case. The MRI in our case revealed brainstem lesions (medial vestibular and prepositus hypoglossi nuclei) and cerebellar lesions, involving the flocculus/paraflocculus, vermis, cerebellar hemisphere VI, VII and uvula, which could explain the above-mentioned abnormal eye movements. The reduced slow phase of OKN and well induced caloric nystagmus seemed to be apparently contradictory results from the point of view of the function of the velocity storage integrator (VSI). However, the impaired OKN was presumably ascribed to insufficient visual inputs conveyed to the VSI from the vestibulocerebellum. Therefore, it was assumed that the function of the VSI was still intact, while the velocity-to-position integrator seemed to show functional deficit.
