Consultant for Pediatricians.
Differentiating Epileptic Seizures From Nonepileptic Spells
By DONALD OLSON, MD |
November 1, 2008
Dr Olson is associate professor of neurology and pediatrics at Stanford University School of Medicine in Stanford, Calif.
Ideally, a seizure event should be captured on EEG, but this is seldom practical in the outpatient laboratory. If the events are reasonably frequent, a long-term EEG that records the habitual attacks helps provide diagnostic certainty.38 Both inpatient and outpatient long-term EEG are feasible, and outpatient video recording during EEG is increasingly practical, but the inpatient setting provides much more control over video recording conditions.
For seizures with altered consciousness, the EEG will almost always show some paroxysmal change, and most of the time an evolving rhythmic ictal discharge will be apparent if the seizures are epileptic. Exceptions include some frontal lobe seizures in which the epileptogenic cortex is distant from recording scalp electrodes, such as in the mesial frontal or the orbital frontal region. Even in such cases, a paroxysmal EEG change, such as slowing, will be evident, but prominent movement artifacts may obscure the EEG. Other exceptions include auras or simple partial seizures. Not enough of the cortex may be synchronized to allow recording of the rhythmic discharges from the scalp electrodes.39
Because it is important that children who are hospitalized for video EEG recordings have their habitual seizures, antiepileptic drugs often are tapered. For patients with mixed epileptic and nonepileptic events, drug tapering presents a problem because drug withdrawal may simply uncover the epileptic attacks that were pharmacologically controlled, although the patient may also experience nonepileptic spells. It is important to document the variety of attacks in question and make sure that the video EEG captures the habitual events and not anomalous seizures that are provoked solely by medication withdrawal.
- The distinction between epileptic seizures and syncope can be particularly challenging. Transient loss of consciousness-particularly if accompanied by body stiffening-can suggest seizures, but positive motor signs are common in syncope.
- Conversion disorders can manifest as psychogenic nonepileptic seizures (PNES) in adults and children. A history of significant social stresses points to the possibility of PNES.
- Behavioral nonepileptic events such as inattention or daydreaming may be hard to distinguish from absence seizures unless there is a clear history of a lack of response to physical stimulation. An electroencephalogram (EEG) is helpful, because untreated persons with absence epilepsy will almost always have generalized spike wave discharges.
- An EEG performed in the first 24 hours after a presumed seizure will show epileptiform abnormalities 51% of the time. Repeated EEGs, sleep deprivation before the EEG, and sleep recorded during the EEG all increase the likelihood of recording epileptiform discharges.
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