Background: The current categorical split of mood disorders in bipolar (BP) disorders and depressive disorders has recently been questioned. The presence of a significant number of manic/hypomanic symptoms in patients with recurrent unipolar depression seems to challenge the traditional dichotomy of unipolar-BP disorder. Two highly unstable personality features, i.e., the cyclothymic temperament (CT) and borderline personality disorder, have been found to be more common in BP disorder than in major depressive disorder.
Aim: The aim was to assess the distributions of the number of mood spectrum, CT, and borderline personality items between two groups. Finding no bimodal distribution (a "zone of rarity") of these items would support a continuity between the two disorders.
Methods: Forty euthymic BP disorder patients and forty unipolar depression patients were administered the Structured Clinical Interview for the Mood Spectrum, which assesses lifetime symptoms, traits, and lifestyles that characterize threshold and subthreshold mood episodes. CT was assessed using Temperament Evaluation of Memphis, Pisa, Paris and San Diego-A relative to CT and borderline personality trait (BPT) was assessed using Structured Clinical Interview for DSM Disorders II personality questionnaire relative to BPT. The distribution of the number of CT and BPT items was studied by Kernel density estimate.
Result: Patient with recurrent depression endorsed manic/hypomanic items though less than BP group. However, the Kernel density estimates distributions of the number of hypomanic/manic items, CT and BPT items in the entire sample had a normal-like shape (i.e. no bimodality).
Conclusion: Normal-like curves in the distributions of mood symptoms, number of CT and BPT items in the entire sample, suggest significant amount of overlap of these characteristic in both the groups. Using the bimodality approach, continuity between BP and major depressive disorder (MDD) seems to be supported, questioning the current categorical splitting of BP and MDD based on classic diagnostic validators.
Keywords: Bipolar disorder; major depressive disorder; mipolar II disorder; mixed depression.