Types of Depression More Frequent in Bipolar than in Unipolar Affective Illness: Results of the Polish DEP-BI Study

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Background: The aim of the study was to assess the relative frequency of various kinds of depression in patients with bipolar and unipolar affective illness. The study was performed in the framework of the DEP-BI project aimed at assessing the prevalence of bipolar disorders among depressive outpatients treated by psychiatrists in Poland. Methods: Eight-hundred and eighty patients (237 male, 643 female) participated in the study. The patients were classified into the following diagnostic categories: bipolar affective illness type I, type II, bipolar spectrum disorder and unipolar affective illness. The various kinds of depression in each group were assessed by means of a semistructured questionnaire added to the diagnostic interview. Results: In the group of bipolar patients, a significantly higher frequency of psychotic depression in male compared to female patients was observed. Male bipolar patients compared with unipolar depressed ones had significantly more episodes of psychotic depression (odds ratio, OR, 4.29) and atypical depression (hypersomnia and hyperphagia; OR 2.82), and those with bipolar spectrum had more episodes of treatment-resistant depression (OR 2.56). Female bipolar patients compared with unipolar depressed ones had significantly more frequently an early onset of depression (before 25 years; OR 2.95) and postpartum depression (OR 2.48). On the other hand, the percentage of agitation, irritability, distractibility, thought racing and panic attacks during depression was not different in patients with bipolar and unipolar affective illness either in males or females. Conclusions: Some kinds of depression occur with a higher frequency in patients with bipolar compared to unipolar affective illness. The occurrence of a given type of depression may constitute an aid for the diagnosis of bipolar illness. The results of this study did not confirm the concept of bipolar mixed depression based on the presence of anxiety symptoms occurring during the depressive episode. The limitation of our study may be the lack of formal criteria or a structured interview to assess the symptoms occurring during depressive episodes.