Background: Although numerous electroencephalographic (EEG) studies have been performed in psychiatric populations, and some have identified specific abnormalities within groups of functional psychoses, differences in EEG findings among subgroups of functional mental illness need to be evaluated with careful consideration of the nosologic systems employed in each study. In the present study, we examined whether there might be EEG differences among subgroups of functional psychoses defined by DSM-IV.
Methods: A total of 143 patients, whose discharge diagnoses met the DSM-IV criteria for mood disorder, schizophrenia, and other psychotic disorders, were studied. EEG findings were compared among seven diagnostic categories: mood disorder without, with mood-congruent, and with mood-incongruent psychotic features; schizoaffective disorder; schizophreniform disorder; brief psychotic disorder; and schizophrenia.
Results: The frequency of epileptiform variants, including the phantom spike and wave, positive spikes, and small sharp spikes, was significantly higher among patients with mood-incongruent psychotic mood disorder (33%), schizoaffective disorder (33%), and schizophreniform disorder (30%), as compared with patients with nonpsychotic mood disorder (3.2%) and schizophrenia (0%).
Conclusions: Our results imply that patients with "atypical" psychoses that are located between typical mood disorder and schizophrenia have similar biological vulnerability, represented by epileptiform EEG variants.