Bipolar type I and II disorders: manifestations of a single disease or two independent nosologies?

The aim is to compare patients with bipolar type I and II disorders according to socio– demographic characteristics, the structure of depressive and hypo-/manic episodes, as well as patterns of concomitant mental disorders. Materials and methods : 173 patients with bipolar disorder were included in this multicenter cross-sectional study, 46.8% of them with type I (n=81). The study participants independently filled out a computerized structured questionnaire for screening for affective disorders, where symptoms of depression and hypo-/mania were recorded. After that, the participants underwent a structured interview with a researcher to verify the diagnosis and identify concomitant mental disorders. The analysis was performed in RStudio version 4.4.0 using the standard R package and the «psych» package. Results : In patients with bipolar type I and II disorders, there were no significant differences in age, sex, and level of education, as well as the frequency of concomitant mental disorders. Patients with bipolar type I disorder were significantly more likely to have symptoms of depression such as psychomotor retardation and thoughts of self–harm or death, and patients with bipolar type II disorder had symptoms of decreased energy levels. In addition, patients with bipolar type I disorder, compared with patients with bipolar type II disorder, were significantly more likely to have all the symptoms of mania, with the exception of hyperthymia and increased talkativeness. Nevertheless, the classification of bipolar type I and II disorders based on cluster analysis for all symptoms of depression and hypo-/mania had sensitivity = 77.92% and specificity = 56.63%. Conclusion : There are no symptoms of depression and hypo-/mania that are pathognomonic only to type I or type II bipolar disorder. Despite some significant differences, clustering-based classification has moderate sensitivity and low specificity. Thus, a single bipolar disorder cannot be divided into two independent nosologies based solely on the structure of mood episodes.