Distinguishing Between Affective Instability, Bipolar Disorder, and Borderline Personality Disorder: Diagnosis and Treatment in an Age of Neuroscience

The zeitgeist of contemporary psychiatry is reflected in a move toward a neurobiological model of psychopathology. Yet there is insufficient knowledge to develop a classification of mental disorders based on neuroscience, and diagnosis continues to be based on observable phenomena, not endophenotypes. The problem is illustrated by the phenomenon of affective instability (AI). This symptom has been assumed to lie in a bipolar spectrum but is more closely linked to borderline personality disorder (BPD), a complex multidimensional diagnosis in which unstable mood is only one feature. This problem demonstrates the need for careful phenomenological study of symptoms, as opposed to assumptions about diagnostic spectra based on superficial similarities.