The "gold standard" in the diagnosis of nonepileptic seizures (NESs) is a recording of a typical event during video-EEG monitoring. This procedure is available at all centers specializing in epilepsy and is increasingly available at general hospitals and even in some neurologic group practices.
During this procedure, the EEG is recorded for a prolonged period, accompanied by continuous closed-circuit video observation. The digitized EEG and recorded behavior are displayed simultaneously, allowing point-to-point correlations of recorded events and any accompanying electrographic changes.
Two types of monitoring are in general use:
Outpatient studies are less expensive and more convenient than inpatient monitoring. DAYMON is most appropriate for patients with relatively high seizure frequencies-at least three events per week. To increase yield, DAYMON should be carried out when the patient is sleep-deprived.
If the patient's seizure frequency is relatively low, inpatient video-EEG monitoring for 24 hours or more is indicated. This procedure requires hospital admission and a dedicated staff. Although more costly than DAYMON, inpatient monitoring is effective. More than one event may be recorded, increasing diagnostic certainty if the events are stereotyped. Inpatient monitoring also allows recording of a full night's sleep, increasing the possibility of recording sleep-provoked epileptiform activity as well as nocturnal clinical events. Several days of monitoring may be required before the diagnosis is made.
During video-EEG monitoring, the patient wears an EEG transmitter connected to a wall outlet by coaxial cable. Wall-mounted video cameras provide continuous behavioral observation. Both EEG and video signals are transmitted to a control room, where the EEG is reformatted and conducted to a video monitor. The EEG signal and video are displayed simultaneously for on-line observation, and both are recorded on videotape. The EEG may be recorded on paper or stored on optical disc.
The patient can move about and carry out normal activities, such as napping, talking, and watching television. Participation by a family member or friend is encouraged, especially someone who has observed the patient's events in the past. Hyperventilation and photic stimulation are carried out. These may cause clinical or diagnostic changes in patients with epileptic seizures but not NESs. Although NESs may occur spontaneously, the application of these procedures appears to increase diagnostic yield.
An important diagnostic aid is suggestion techniques to precipitate one of the patient's usual events. These techniques may take the form of placing alcohol pads over the carotid arteries or administering intravenous saline. The patient is told that the procedure will be carried out to induce a seizure and that only by recording an event will a diagnosis be possible. If an event is precipitated and the event is typical of the patient's usual seizure, a diagnosis of NESs is highly likely. False positives are rare. When DAYMON is performed in this manner, an overall success rate of approximately 60% may be expected (French 1993). There are some ethical concerns about the use of deception, although definitive diagnosis can allow patients to obtain proper therapy and avoid unnecessary antiepileptic drugs, with their side effects.
During NESs, the EEG will show:
Although the EEG tracing is frequently obscured by movement artifact, small interpretable segments containing alpha activity may be apparent, indicating that consciousness is preserved.
A normal or nonepileptiform EEG during a seizure may suggest a NES, but it can also occur during a simple partial seizure or frontal lobe complex partial seizure undetected by surface leads. A normal EEG during a seizure in which the patient is displaying generalized motor movements would not be expected in a true epileptic seizure, however.
The most important task is to ensure that the recorded event(s) are typical of the patient's spontaneous attacks. This task can be accomplished only by reviewing the recorded attack with a person who has witnessed such events. If it is determined that the recorded and spontaneous attacks are similar, a presumptive diagnosis of NESs can be made.
Some clinicians require that more than one attack be recorded, but this is not always possible. Nonetheless, it appears that a single recorded event similar to previous attacks is sufficient to consider NESs the most likely diagnosis.
This diagnosis, of course, does not exclude the possibility of coexisting epilepsy, especially if the patient has attacks with different clinical features. Some epilepsy patients experience psychogenic nonepileptic seizures at some point, and patients with psychogenic nonepileptic seizures can have neurologic illness.
The interictal EEG is not useful in making the distinction because it may be normal or abnormal in either case. The interictal EEG of patients with NESs may contain epileptiform discharges, even though the ictal record does not reveal electrographic seizure activity.
If intensive video-EEG monitoring is not available, a diagnosis of NESs can be made with reasonable assurance using commonly available tools. Probably the best method is to obtain an EEG after the patient is sleep-deprived. A video camera can be set up in the EEG room. During the recording, and after explaining the procedure, apply techniques of suggestion, emphasizing the importance to the patient of recording an event.
The use of 24-hour ambulatory cassette EEG recording to diagnose NESs is not recommended unless a home video unit is available. Unless the behavioral aspects of the attack are recorded, there is too little diagnostic information. Moreover, excessive EEG artifacts during an attack often makes it very difficult to interpret the cassette EEG. If the patient has attacks characterized by staring with little motor activity, a cassette EEG can be useful. Certainly, differentiation of absence seizures from NESs characterized by loss of awareness is relatively easy. Again, simultaneous video recording greatly enhances diagnostic power.
Reviewed and revised February 2004 by Orrin Devinsky, MD, New York University
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