Symptoms of borderline personality disorder (BPD) and bipolar disorder (BD) often overlap. In some cases, it is difficult to conduct a differential diagnosis based only on current diagnostic criteria Therefore, it is important to find clinical factors with high discriminatory specificity that, used together with structured or semi‐structured interviews, could help improve diagnostic practice.
We propose that a clinical analysis of identity, self‐concept and self‐esteem may help distinguish the two disorders, when they are not co‐morbid. Our review of the studies that analyse these constructs in BD and BPD, separately, points in the direction of qualitative differences between the two disorders. In BPD, there is a well‐documented identity diffusion, and the self‐concept appears predominantly negative; shifts in self‐concept and self‐esteem are often tied to interpersonal triggers. In BD, patients struggle with their identity, but narrative identity might be less compromised compared with BPD; the shifts in self‐concept and self‐esteem appear more linked to internal (i.e. mood and motivational) factors. We end the paper by discussing the implications for clinicians and ideas for future comparative research.