Magnetoencephalography in the detection of focal lesions in West syndrome

Background: According to the international classification of epilepsy syndr omes, West syndrome (WS) is a form of generalized epilepsy. However, it is known that localized lesions can induce WS and that patients with WS often subsequently develop focal seizures. We evaluated such patients using magne toencephalography (MEG). Method: Fourteen patients of 3 months to 6 years of age who had or who had previously had WS were examined. MEGs were recorded using a laying-type A h ole-cortex MEG system with a 160-channel first-order gradiometer. Twelve-ch annel electroencephalography (EEG) and one-channel electrocardiography (ECG ) were simultaneously recorded. Equivalent current dipoles were estimated a t the point of spikes on the EEG. Results: Patients were classified by magnetic resonance imaging (MRI) findi ngs into a focal lesion group (group F, n = 7) and a non-focal lesion group (group N, n = 7). The dipoles estimated from the MEG were classified into three groups: W, with the dipoles distributed over a wide brain area (n = 7 ); WC, dipoles distributed over a wide area along with a dense dipole distr ibution in a specific cortical area (n = 3); and C, closed dipole distribut ion in a unilateral cerebral focal area (n = 4). Patients were also classif ied by the stage of the disease during which the MEG was recorded, and by t he type of seizure they experienced. Those with hypsarrhythmia examined ear ly in the disease all had pattern W regardless of their lesion group, where as those examined later exhibited more diverse dipole patterns that corresp onded to seizure type. Conclusions: Dipoles were distributed widely over bilateral cerebral cortex when patients had infantile spasms with hypsarrhythmia whether or not they had focal lesions. The dipole distribution pattern in MEG changed accordin g to changes in seizure type. (C) 2001 Elsevier Science B.V. All rights res erved.