Presence and Overlap of Bipolar Symptoms and Borderline Features during Major Depressive Episodes

Background: Bipolar symptoms and borderline personality features occur in both unipolar and bipolar major depressive episodes (MDEs). We investigated their prevalence, severity, co-occurrence and overlap.

Methods: We interviewed 124 psychiatric outpatients with MDE using the Structured Clinical Interview for DSM-IV-TR Axis I and II Disorders, the Borderline Personality Disorder Severity Index (BPDSI-IV), and about past (hypo)manic episodes, and stratified them according to the principal diagnosis into subcohorts of major depressive disorder (MDD, n = 50), bipolar disorder (BD, n = 43), and borderline personality disorder (BPD, n = 31). We quantified (hypo)manic symptoms using a novel semi-structured interview (MIXed symptoms during MDE, MIX-MDE) with good psychometric qualities.

Results: The subcohorts did not differ in MDE severity. They differed significantly in some (hypo)manic symptoms being present on most days in 24% of MDD, 30% of BD, and 42% of BPD subcohort, but only 5% of the BD subcohort fulfilled the DSM-5 mixed features. The mean MIX-MDE scores were 5.7 (SD 4.0), 12.0 (8.2) and 10.5 (7.5), and BPDSI-IV scores 15.6 (7.0), 17.2 (6.2) and 26.9 (8.7), respectively (both p <0.001). (Hypo)manic days and unspecific symptoms of distractibility and irritability inflated the correlation of observed (hypo)manic symptoms and borderline features.

Limitations: Moderate sample size, limited age variation (18-50 years); no previous validation of MIX-MDE.

Conclusions: Presence of some mixed and borderline features is common in MDEs, with overlap and diagnosis-specific differences. Unspecific symptoms of irritability and distractibility and the aggravating impact of hypomania on perceived BPD features blur the differential diagnosis.