Ictal symptoms and signs reflect area(s) of the brain involved in the seizure. Events early in the seizure have greater localizing value than later ones as these latter may result from propagation. As certain symptoms, such as a rising abdominal sensation in a focal seizure, may result from involvement of any one of two or more anatomically distinct regions usual accompanying phenomena may help to distinguish possible ictal areas of origin. Therefore, a cluster of patient- and observer-reported phenomena will more accurately chart seizure origin and propagation than will a single symptom or sign. Knowledge of cortical, thalamic, and brain stem physiology will equip the physician with insightful questions of the patient and associates and will allow perceptive evaluations of video-telemetry seizure depictions. Not only will such scrutiny localize most focal seizures but also it will often distinguish primary generalized from secondarily generalized seizures.1
Precipitating factors such as flashing lights or sleep deprivation need be sought. Enquiry about lifestyle may disclose potentially alternative diagnoses, such as excessive daytime sleep in a child thought to have absence or dyscognitive (temporal lobe) seizures. Epilepsy is likely more often overdiagnosed than underdiagnosed. Social and psychological consequences of incorrect diagnoses are difficult to reverse.2
As some phenomena will localize but not lateralize to a neural system, that is, visual or limbic, the neurological examination may help to determine the side of epileptogenesis. A decreased nasolabial fold or impaired fine finger movements are two of many physical signs of potential ictal lateralizing value. Moreover, normal aspects of the examination may eliminate certain regions, for example, full visual fields for calcarine occipital seizure onset. Therefore, thoughtful clinical evaluation will develop specific questions for electroencephalography (EEG), thus enhancing its value.
Appropriate questions for EEG derive from the clinical evaluation and include: (1) does the child have epilepsy; (2) what type is present—focal, generalized, or secondarily generalized; (3) what is its severity and thus its prognosis; and (4) are there any avoidable precipitating factors?
In addition to an understandable concern about overlooking a significant EEG phenomenon, three factors can lead to overinterpretation of EEGs, particularly pediatric EEGs.
The first are sharply contoured artefacts such as muscle, sudden movement, electrode malfunction, and bottle-sucking. Before assigning any label to a waveform, think artefact first.
Secondly, nonartefactual apiculate (sharply contoured) waveforms usually appear in normal background activity of childhood, especially while awake or drowsy. These potentials are either apiculate in themselves or combine with other, smoother waveforms to create an apiculate morphology. As rich mixtures of waveforms appear in the posterior head, central and temporal regions; nonspike apiculate waveforms occur particularly often at these sites.
The following criteria help to identify real spikes in this apparent minefield: (1) the discharge should be paroxysmal, that is, clearly distinguished from background activity; (2) ...