To examine clinical, electrophysiological differences among subgroups of schizophrenic patients with different QEEG profiles identified by cluster analysis.

Fifty-two schizophrenic patients were studied (age:34.64 ± 10.41, 18–58 years). Digital, resting electroencephalogram was recorded and submitted to quantitative-topographic spectrum analysis (QEEG), and patients’ clinical state was assessed by the Greek version of Positive and Negative Syndrome Scale (PANSS). QEEG data were submitted to cluster analysis, and QEEG, clinical differences were compared using Kruskal-Wallis non-parametric test.

Three groups of patients with different electrophysiological profiles (p < 0.05) were detected by cluster analysis of QEEG data: Group A, characterized by increased levels of relative power in α frequency band, low levels in β, medium levels of relative power in δ, θ frequency bands; Group B, characterized by increased levels of relative power in δ, θ frequency bands and medium in α, β; Group C, characterized by increased levels of relative power in β frequency band, very low in α, medium in δ, θ bands. According to PANSS, group A patients had lower (p < 0.05) levels of agitation, hostility/aggression, difficulty in abstract thinking, stereotypic thought and attention deficit than patients of the other groups.

Cluster analysis can be used to identify characteristically different QEEG profiles of schizophrenic patients. The cluster with increased relative power in the α frequency band, low levels in β, and medium in δ, θ bands was “healthier” in specific PANSS parameters than the clusters with low α and increased relative power in δ, θ and β frequency bands.