EEG spikes resembling cardiac M-shaped waves in the EKG: the cerebral M pattern

Abstract

Interictal epileptiform discharges (IEDs) in the electroencephalogram (EEG) are electroclinical patterns typified by sharp waves and spikes, and defined as waveforms that are distinct from the background activity due to their high amplitude (typically 2.5-fold higher than the background voltage). Their duration may vary from less than 70 ms (classified as spikes) to 70-200 ms (classified as sharp waves). There is a large body of literature on the characteristics of typical IEDs 1-5 but a paucity of data on atypical IEDs.All scalp-recorded electrical activities are generated by postsynaptic potentials in cortical neurons. It is hypothesized that IEDs represent the summation of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials in the cortex. IEDs in scalp recordings typically have a negative polarity that reflects the action of perpendicularly oriented neurons in the cortex. However, it is noteworthy that in certain types of cerebral insult (particularly congenital CNS anomalies), augmentation of the deep cortical EPSPs may Studies of interictal epileptiform discharges are essential for improving the diagnosis, classification, and management of epilepsy. In this case series we sought to identify the clinical and neurophysiological significance of bifid spikes, whose pattern bears a strong resemblance to the cardiac M pattern. We hypothesize that, analogous to the cardiac M pattern, the cerebral M pattern is generated by a conduction defect associated with asynchronous spatiotemporal averaging of electrical signals in the cortex, resulting in the signals reaching the scalp with different latencies. Unlike the cardiac M pattern, the pathology underlying the cerebral M pattern is unknown, although congenital CNS anomalies may be a culprit.

Atypical Interictal Epileptiform Discharges in Electroencephalography

“…Theoretically, this process is triggered by cortical deafferentation due to a sub-cortical pathology. Bifid spikes17 and “notched” delta18 are presumed to emanate from conduction defects in projection fibers, resulting in the electrical signals reaching the scalp with different latencies, configuring a “notched” appearance.…”