Abstracts

Rationale: Focal slowing is often interpreted as a sign of an underlying structural lesion. This is largely based on studies of adults. We examined the frequency of MRI demonstrated structural abnormalities in patients with focal slowing on the EEG and the concordance between the EEG and MRI features.Methods: EMU reports were retrospectively reviewed for children with non-syndromic epilepsies (3m to 19y). All children with reports of focal slowing and who had a MRI scan were included. Localization was categorized as temporal (T), anterior (AT), posterior quadrant (PQ) and other (subcortical, hemispheric, multifocal, diffuse). Side was left only, left>right (L), bilateral (B), right>left, or right only (R). The depth of the lesions were categorized as: cortical gray matter only(CGM); cortical white matter only(CWM); both of CGM and CWM; the junction of CGM and CWM; and Multilayer.Results: Of 105 included children with focal slowing, 76(72%) had abnormal MRIs. The types of structural lesion were malformation of cortical development (MCD) in 29/76(38%) , atrophy in 12/76(16%) and stroke in 8/76(11%) cases. The depth of lesion were both CGM and CWM in 19/76(25%) , Multilayer in 17/76(22%), CGM in 15/76(20%) and CWM in 10/76(13%) cases. When the MRI was abnormal, the side of abnormality was concordant with side of slowing in 50(66%) cases. The location of MRI abnormality and focal slowing were concordant in 32(42%). There were 69(66%) children who had interictal epileptiform discharges IEDs, and 54 of these had an abnormal MRI. Side of IED and MRI abnormality were concordant in 36/54(67%) cases. Location was concordant in 23/54(43%) cases. Slowing and IED side were concordant in 59/69(86%) cases and concordant for localization in 49/69(71%) cases. Focal slowing in temporal and anterior regions was more likely to indicate a lesion in these regions whereas posterior quadrant slowing was equally associated with a PQ lesion or a lesion elsewhere. (See table.1)Conclusions: 1. Focal slowing in children evaluated for epilepsy is strongly indicative of an underlying structural lesion, most of them involving several brain layers. MRI is essential if focal slowing is found. 2. The localization of either slowing or IED is only partially correlated with location of the structural abnormality. Of particular interest to us was the fact that lesions in the temporal lobe may have associated slowing in the posterior quadrant, considerably behind the actual lesion. 3. Interictal epileptiform discharges and focal slowing are highly concordant.