Ictal Nystagmus by Epileptic Activation of Cortical Smooth Pursuit System: Electrophysiological and Neuroimaging Study

Background: Epileptic nystagmus is rare. There is no report in Korea about epileptic nystagmus by the activation of cortical smooth pursuit area. We studied a 29-year-male patient with nonconvulsive simple partial status epilepticus presenting as pure ictal nystagmus. Methods: The EEG including electrooculogram and electronystagmogram during ictus was done. Brain MRI including 99mTc-ECD SPECT and 18F-FDG PET were also done during ictus and repeated after complete relief from symptom. Subtraction images obtained from each of SPECT and PET were coregistrated onto MRI. Humphrey visual field test was done for documentation of visual field defect. Results: EEG was compatible with nonconvulsive status epilepticus arising from right mesial occipital area with 9-10 Hz frequency. Compensatory left beating nystagmus with midline crossing feature was noted and characteristic ipsiversive linear slow phase was presented in electronystagmogram. Brain neuroimages from MRI, 99mTc-ECD SPECT, and 18F-FDG PET revealed that the right parietotemporooccipital area was relevant area, but the right frontal eye field area was spared, which was much clear in SISCOM image. Conclusions: Clinical feature and electronystagmogram in this case showed typical epileptic nystagmus by activation of cortical smooth pursuit regions in which the relevant regions was posterior parietotemporooccipital area. The sparing of the frontal eye field area in this case suggested clearly that the epileptic nystagmus by the activation of cortical smooth pursuit regions could occur without involvement of frontal eye field area.ope