Benign encephalitis: electro-oculographic analysis of opsoclonus

Two cases of benign encephalitis are described, which showed opsoclonus associated with myoclonic jerks of the body and face, and with cerebellar dystaxia in one case. EOG and EEG analysis during the course of these cases showed: 1. opsoclonic eye movements were triggered by saccadic and non-saccadic eye movements, 2. decrease of luminancy and loss of fixation were releasing, but not triggering opsoclonic bursts during the initial stages, 3. eye closure had the strongest trigger effect, which lasted very long and allowed an objective description of the (benign) course of the illness, 4. besides conjugate, mostly horizontal, spontaneous eye movements oblique and vertical ones were also obtained. Monocular and disconjugate eye movements were seen only during the initial stages, 5. statistical analysis of the frequency of single eye movements during periods of opsoclonic bursts showed that, in the course of the disease the variability of frequencies decreased and the degree of fast frequencies increased, particularly with open eyes, 6. the frequent coincidence of opsoclonus and lesions of the cerebellum or of the cerebellar pathways is striking, but the initially distinct EEG changes, the very different trigger modes and certain pathoanatomically described cases without any cerebellar lesion indicate the more general character of the disturbance. 7. the entity of opsoclonus, body tremulousness, and benign encephalitis has to be differentiated from other syndromes including the sign opsoclonus by recording the EEG and EOG during the course of the disease; this might lead to very useful diagnostic and prognostic information.