Generalized 3-Hz spike-and-wave complexes emanating from focal epileptic activity in pediatric patients

Abstract

We describe two pediatric patients with an uncommon electrophysiological seizure propagation pattern. Both had dialeptic seizures as the main or only symptom. Case 1 had a small mass in the left medial temporal structures; case 2 had no lesion on magnetic resonance imaging. In both, the electroencephalogram showed not only left temporal spikes, but also bilaterally synchronous 3-Hz spike-and-wave complexes (SWCs) from onset and unusual secondarily generalized 3-Hz SWC patterns arising from the left temporal region. Case 1 was seizure free following resection of the mass; focal or generalized epileptiform electroencephalographic abnormalities were no longer present. In case 2, magnetoencephalography localized the spikes to the left superior and midtemporal gyrus, which ictal single-photon-emission computed tomography suggested was the origin of onset. These cases illustrate the close relationship between the focal epileptic area and 3-Hz SWCs and suggest that the focal area can trigger 3-Hz SWCs. The therapeutic strategy may need to be altered in such patients.

Fig. 1

Representative EEG activity in Case 1. (a) single spike in the left temporal area, (b) synchronous generalized 3 Hz spike-and-wave complexes from seizure onset, and (c) secondarily generalized 3 Hz spike-and-wave complexes. After undergoing resection of a tumor in the left temporal lobe, the patient was seizure-free, and the epileptic activities shown here also disappeared completely.

Fig. 2

(A) Case 1: Presurgical MRI of Case 1 showing a lesion in left temporal lobe, approximately 2×2 cm, which enhances with gadolinium (white arrow). (B) Postoperative MRI of Case 1 showing complete surgical resection of the brain tumor. (C) Case 2: Superimposed spike dipole on a coronal image of patient’s individual MRI. Note that the spikes, shown in Fig. 3 as (a), (b), and (c), are estimated to come from left temporal area. (D) Case 2: Subtraction ictal SPECT with 99m-Tc ethyl cysteinate dimmer. Note that the hyperperfusion (defined as over 2 with a Z score) occurs in the left superior to middle temporal gyrus.

Fig. 3

From top, EEG and MEG waveforms, magnified spike waveform, contour map of MEG, and dipoles on individual MRI of representative epileptic discharges are shown for Case 2. (a) single spike in the left temporal area, (b) synchronous generalized 3 Hz spike-and-wave complex from seizure onset, and (c) secondarily generalized 3 Hz spike-and-wave complex. MEG: The analyzed portions of the MEG waveform are indicated by the broken box. Note that MEG tends to show spikes with greater clarity than EEG. The time latency between the left and right epileptic discharges during generalized spikes, seen in panel b, is 7 ms. Contour maps: Arrows on the contour maps indicate the estimated dipoles. The solid line indicates magnetic field efflux, and the broken line indicates magnetic field influx from the brain surface. MRI: The circle and bar shown on the MRI scans indicate the dipole location and orientation, respectively.