Focal triphasic sharp waves and spikes in the electroencephalogram.

Abstract

There is a plethora of data in the EEG literature on the characteristics of the most prominent component of interictal epileptiform discharges (IED), namely the negative (fast) phase. Surprisingly, however, little attention has been drawn to the after-coming slow wave (ASW), and its pathological as well as clinical significance. In this paper, we will address the significance of prominent (high amplitude) ASW, giving rise to a triphasic morphology of the IED (focal triphasic sharp waves and spikes—FTSW). We will discuss this EEG pattern with respect to its clinical, neurophysiological, and neuropathological significance. This investigation was conducted on a heterogeneous group of patients at KKH, Ha'il, KSA. Our data revealed that FTSW were rare EEG events occurring primarily in the first two decades of life. Ninety percent of the patients with FTSW had epilepsy, presenting clinically with generalized convulsive seizures, often without partial onset. The majority of these patients responded favorably to anticonvulsant monotherapy. We were surprised to find that half of the patients with FTSW had chronic and/or static CNS pathology, particularly congenital CNS anomalies. Even though more than one mechanism may be involved in the pathogenesis of FTSW, we believe a deeply seated pacemaker as the source of this EEG pattern is the most compelling theory. The presence of FTSW should alert clinicians to the possibility of an underlying chronic and/or static CNS pathology, in particular congenital CNS anomalies, underscoring the significance of neuroimaging in the work-up of this population. Moreover, it is conceivable that the prominent ASW may contribute to the interictal intellectual dysfunction of these patients, justifying aggressive anticonvulsant therapy.