Interictal EEG Abnormalities in Patients with Psychogenic Nonepileptic Seizures
Reuber M, Fernández G, Bauer J, Singh DD & Elger CE;
Commented by , 21 Oct 2002
Background
The management of suspected nonepileptic seizures can be complicated by more or less specific abnormalities in the EEG. Ideally the diagnosis should be based on video-EEG, and the patients should not receive treatment with antiepileptic drugs (AED), although this is not true in many cases.
It has been reported that the prevalence of interictal changes is increased in patients with psychogenic nonepileptic seizures (PNESs), but the diagnostic significance of these changes has never been described.
Aim
To examine interictal EEG abnormalities in patients with PNESs.
Methods
The study was retrospective and included EEG reports of 187 consecutive patients with PNESs. The diagnosis was established by video-EEG/EEG and expert observation (80.2 %), or if PNESs had occurred spontaneously in front of an experienced epileptologist (19.8 %). A diagnosis of coexisting epilepsy was based on video-EEG/EEG (43.9 %), or clinical assessment by an experienced epileptologist (56.1 %).
To investigate whether PNESs alone are associated with an increased prevalence of interictal EEG changes, EEGs of PNES patients without any other known cause of EEG disturbance (N = 50) were analyzed with EEGs of healthy matched controls (N = 50). All EEGs were reported by two blinded experienced epileptologists, and all discrepant reports were reviewed by an EEG board examiner.
Results
Of all 187 patients with PNESs 57 had also epilepsy. The remaining 130 patients showed higher rates of nonspecific (53.8 %) and epileptiform EEG abnormalities (12.3 %) compared to the general population (p < 0.001). In the controlled study, EEG abnormalities were 1.8 times more common in patients (18 %) than in controls (10 %) (no statistical significance; p = 0.19). The frequency of epileptiform EEG changes was similar to previous reports (2.0 %).
Discussion
The study describes a two-fold increase in the prevalence of EEG abnormalities in patients with PNES compared to previous reports. The authors speculate that more frequent EEGs carried out in the current study, more sensitive EEG recordings, more frequent use of AED and possible overreporting of EEG might account for some of this discrepancy.
In the controlled study, where patients had no clinically recognizable cause of EEG disturbance, the frequency of EEG disturbance dropped to 18 % in the PNES group. The authors suggest that the most likely explanation for this is that organic brain dysfunction is an important risk factor for the development of PNESs. EEG changes were seen 1.8 times as often as in the controls.
This figure was not statistically significant, which could be explained by the fact that selection and reporting bias was removed from the controlled part of the study. Although the conclusion of the study in this regard is weak, it provides important information regarding the prevalence of PNESs, the clinical evaluation of PNESs and potential risk factors. Furthermore the study states the necessity of not starting inappropriate AED treatment on the basis of nonspecific EEG changes.