Abstracts

Rationale: Frequent epileptiform discharges lead to transient cognitive impairment and may contribute to learning disability and developmental delay in pediatric epileptic encephalopathies (Semin Pediatr Neurol. 1995;2(4):246-53). Although the anatomic substrate of interictal epileptiform discharge sleep-potentiation and increased nocturnal spike wave index is not yet fully understood, thalamic dysfunction has been suspected. Accordingly, the overall objective of the present study was to identify the frequency of thalamic MRI lesions in patients with sleep potentiated spiking and to correlate findings with the spike wave index. Methods: Data from 3000 longterm video-EEG admissions over an 8 years period were retrospectively reviewed for clinical presentation, EEG, and neuroimaging findings. The brain MRIs of patients with sleep-potentiated interictal epileptiform discharges were reviewed by two independent reviewers in order to identify thalamic involvement. Spike-wave index (SWI) was calculated as percentage of one-second bins containing at least one spike in the first five minutes of each hour of non-REM sleep. Results: 147 patients with sleep-potentiated epileptic spikes who also underwent a brain MRI were identified. Brain MRI was abnormal in 44 patients. Fourteen patients of those with MRI abnormalities (32%) had either signal abnormalities or volume loss in the thalamus (8 left sided, 2 right sided and 4 bilateral). Eleven had periventricular leukomalacia (PVL) or perinatal stroke, 2 had malformation of cortical development and 1 had lateralized hemispheric signal change consistent with Rasmussen encephalitis. Patients with thalamic involvement had a significantly higher average SWI (73%) relative to patients without thalamic lesions (45%; p<0.05). These groups did not differ with regards to age of diagnosis, frequency of language problems, autistic spectrum disorder, or occurrence and frequency of seizures. PVL (p<0.01) and perinatal strokes (p<0.01) were more frequently seen in patients with thalamic lesions. Conclusions: Structural lesions involving the thalamus may contribute to sleep potentiation of epileptic spikes and to an increased SWI. Disrupted thalamo-cortical circuits, possibly in the setting of PVL or early acquired strokes may play a role in the generation of frequent nocturnal spiking. Careful examination of the thalamus in patients with abnormal neuroimaging may assist in the earlier identification of the patients at risk for electrical status epilepticus in sleep, regional sleep potentiated spiking and related neurologic morbidity. Similarly, detailed anatomic imaging of the thalamus, and perhaps of the thalamo-cortical white matter connectivity may be warranted in patients with sleep-potentiated spikes on EEG.