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Psychogenic Nonepileptic Seizures
Abstract & Commentary
By Steven Karceski, MD, Director of Clinical Trials, Cornell Comprehensive Epilepsy Center, Weill Cornell Medical College. Dr. Karceski reports he is on the speakers bureau for GlaxoSmithKline, Cyperonics, and Pfizer; and receives research support from Novartis and Cyberonics.
Synopsis: Frontal lobe dysfunction may presdispose people to have psychogenic nonepileptic seizures; this dysfunction can be measured by analyzing a brief period of the awake EEG.
Source: Knyazeva MG, et al. Psychogenic seizures and frontal disconnection: EEG synchronization study. J Neurol Neurosurg Psychiatry 2011;82:50-58.
Knyazeva and her colleagues used eeg in a novel way to look for differences in brain wave activity in people with psychogenic nonepileptic seizures (PNES). Like epileptic seizures, nonepileptic psychogenic seizures are episodes of transient neurological dysfunction. However, unlike epileptic seizures, PNES occur without the simultaneous, abnormal, evolving electrical potentials that are recorded during epileptic seizures. The lack of changes during the event (aka, the ictus) is one of the features of PNES that distinguishes it from other nonepileptic events like syncope. In short, the EEG is normal during PNES. EEG, and very often video-EEG, is the medical test that is most helpful when trying to differentiate between these types of events.
Knyazeva et al used the EEG in a novel way. Instead of looking at the ictal EEG (i.e., the EEG during the ictus), they looked at a 3-4 minute segment of awake-only EEG. They analyzed the interictal (between event) EEG, looking for patterns of synchronization between the hemispheres. They studied 13 patients with PNES and compared these to age- and sex-matched controls (people without seizures). They found that in the group with PNES, there was a hypersynchronization of brain wave activity in the left frontotemporal, left parietotemporal, and left central brain regions. They concluded that interictal EEG, when analyzed in this way, suggests that there is a brain substrate for PNES. Further, the region of abnormality may reside in the left frontal lobe. In short, the frontal lobe dysfunction may predispose the person to PNES.
PNES largely has replaced the older term pseudo-seizures. The reason for this is simple: the prefix pseudo- suggests that the seizures are "fake." In other words, a person who has PNES is "faking it." This could not be further from the truth in the vast majority of instances. Although true malingering is rarely encountered, most people with PNES are experiencing a somatization disorder, which falls under the broader category of conversion disorder. In other words, the person is subconsciously manifesting a psychic trauma in a physical way.
PNES is a relatively common illness. It can occur at any age (ranges include as young as 4 years old to 77 years old). The prevalence of PNES is estimated to be 0.5% of the general population. In comprehensive epilepsy centers, up to 20%-50% of patients will carry the diagnosis of PNES, whether as a sole diagnosis or in combination with epileptic seizures. Fifty percent to 70% of people with PNES have an associated psychiatric illness.
PNES and epileptic seizures can be difficult to distinguish from each another. Video-EEG records both the clinical manifestation of the event and the electroencephalogram. Both are then reviewed and carefully analyzed. Although there are pitfalls to the analysis, in most instances, this technology can separate epileptic seizures from PNES.
In their paper, the authors suggest that the EEG between events is also important. By analyzing this, there may be subtle differences in brain wave patterns. These differences suggest that there is a brain substrate for PNES. Their findings (primarily in the left frontal lobe; more specifically the prefrontal region) are similar to other reports of prefrontal dysfunction. For instance, prefrontal activation has been shown to occur in other conversion disorders like psychogenic paralysis (using functional MRI and positron emission computed tomography studies). In short, the findings coincide with other studies of somatization disorders.
This idea is not new. For many years, PNES has been observed to occur after traumatic brain injury. PNES have also occurred in people with prior CNS infection, stroke, and demyelinating disease. The most common association is between PNES and another psychiatric illness like depression or anxiety.
The authors admit that their study is limited. The population is small in number. Most of the study patients were taking medication (most often a benzodiazepine) and controls were not. Benzodiazepines cause changes in EEG increase in frontal lobe fast frequencies. It is possible that the benzodiazepines were responsible for the subtle changes in recorded synchronization.
All patients had video-EEG to confirm the diagnosis of PNES. However, it is not clear whether some of them also may have had epilepsy. This is an important distinction to make, especially since the two conditions can overlap.
Finally, it is not clear whether the observed changes could be due to a psychiatric illness. Focal dysfunction, as measured by functional brain imaging, has been reported in people with depression. Most often, this has been reported in the right hemisphere. In other words, the focal brain synchronization that Knazeva reported could indicate a brain substrate for the psychiatric illness, and not PNES.
It is clear that more study is needed. Careful analysis of interictal EEG may reveal abnormalities in many different medical illnesses. They also may occur as a result of medications that are active in the central nervous system. By studying these differences carefully, scientists may uncover information that expands the understanding of illnesses like PNES. Improved diagnostic testing may lead to earlier diagnosis, and ideally, improved treatments.