Abstract
We report a case of divergence nystagmus recorded by ENG, review the literature and discuss the probable etiology.
A 72-year-old male had had cardiac arrhythmia for several years. He complained of blurred vision and unsteady gait after an episode suggestive of cerebrovascular disorder. CT scan revealed a small low density area in his brain-stem. The neurological examination was normal except for eye movements. Neuro-otological examination showed divergence nystagmus on primary eye position, horizontal gaze nystagmus on both sides, direction changing positional nystagmus to the nasal side, no abnormality of saccadic or smooth pursuit eye movements, slightly reduced optokinetic response and normal caloric response with normal visual suppression. There were no abnormal findings on audiological examination.
Divergence nystagmus is a very rate phenomenon in clinical practice. We could find only 6 case reports, some of which cannot be considered thorough by studied. There has been no general agreement on the responsible lesion or mechanism.
In our case, CT of the brain revealed a small low density area in the pons, but we cannot immediatedly conclude that the focus of divergence nystagmus is in the pons. Recent studies, however, suggestthat not only a convergence but also a divergence center exists in the tegmental area of the mid-brain.
