Cognitive and Behavioral Differentiation of Those With Borderline Personality Disorder and Bipolar Disorder

The current study sought to identify features offering differentiation of borderline personality disorder (BPD) from bipolar disorder (BP). Participants were clinically assessed and assigned diagnoses based on the Diagnostic and Statistical Manual of Mental Disorders criteria. A 113-item self-report questionnaire was completed, comprising cognitive and behavioral constructs weighted to a borderline personality style. A total of n = 53 participants were assigned to BPD, n = 83 to BP, with comorbid participants excluded. Twenty items were highly endorsed (>95%) by the BPD group, with most of the features capturing emotional dysregulation (ED) and identity disturbance; however, many items were also highly endorsed by the participants with BP. Thirty-eight items offered differentiation of BPD from BP, with identity disturbance overrepresented. The study findings indicate that the transdiagnostic nature of ED (a feature of both conditions) means it is less useful for diagnostic decisions, whereas identity disturbance is both intrinsic to BPD and offers specificity in differentiation from BP.