ABSTRACT
PURPOSE: A hypomotor seizure is a useful descriptive terminology, but its clinical and ictal characteristics are not fully understood. We investigated the clinical and electrophysiological characteristics of hypomotor seizures in children. METHODS: We reviewed 394 video-taped recordings, performed between Dec. 1994 and Feb. 2003., to select patients of hypomotor seizures. Exclusion criteria were as follows; i) hypomotor seizures accompanied with other types of seizures in a single event, ii) patients without neurocognitive dysfunctions who were older than 3 years old, iii) non-convulsive status epilepticus, iv) poor video quality. A total of 329 hypomotor seizures from 42 patients (M:F=27:15) were included. The mean age of onset was 1.9 years old, the mean age at the monitoring 4.5 years old, and the mean duration of follow-ups 3.9 years. RESULTS: Thirteen patients (31%) showed generalized onset, hypomotor seizures while 29 patients (69%) showed partial onset hypomotor seizures. 35 patients (83.3%) had neurocognitive deficits. Significant abnormalities in the on brain MRIs were revealed in 23 patients (54.8 %). The concordance rates of interictal epileptiform discharges were 29.0%. In 8 patients, (hypomotor seizures were separately accompanied by other types of seizures (19.0%)). Comparing generalized seizures (group 1) with partial seizures (group 2), there were no significant differences in the clinical parameters between the two groups. In brain MRIs, group 2 tended to have focal lesions. On the analysis of ictal rhythms in group 1, diffuse spike and wave discharges were noted in 8 patients, rhythmic beta in 2 patients, semirhythmic theta in 1 patient, diffuse attenuation of the background in 1 patient, and bilateral beta in 1 patient. Among 5 patients with ictal rhythms other than diffuse spike and wave discharges, 4 patients were younger than 3 years old. On the analysis in group 2, rhythmic ictal patterns were noted in 24 patients (82.8%), seimirhythmic in 2 patients (6.9%), and irregular in 3 patients (10.3%). The distribution of ictal frequencies was as follows:alpha in 3 (10.3%), beta in 4 (13.8%), theta in 10 (34.5%), delta in 4 (13.8%), repetitive spikes or sharp waves in 5 (17.3%), and spikes and waves in 3 (10.3%). Rhythmic beta patterns tended to be localized into the posterior quadrant. CONCLUSION: Hypomotor seizures consist of generalized-onset (31%) and partial-onset (69 %). No clinical parameters can predict the ictal patterns. Various patterns in patients with generalized onset hypomotor seizures under 3 years old may suggest different mechanisms of generalized hypomotor seizures from absence seizures. Rhythmic beta patterns from the posterior quadrant may suggest the localization-specific ictal patterns.