You suspect a patient is describing the experience of multiple personalities. Before revealing the answer, decide how you would assess for this.

Ask the patient to describe their experience in detail, listening for a description of experiencing more than one distinct personality, each with its own characteristics, rather than a single self that has changed over time. Given its recognised diagnostic complexity and controversy, approach the assessment with careful, thorough differentiation from a range of other conditions with overlapping features, rather than accepting the presentation at face value without further exploration. Given the frequent association, per its DSM-5 description, with a history of significant trauma, particularly childhood abuse, take a careful, sensitively handled developmental and trauma history where clinically appropriate. Distinguish this carefully from the milder, more common experience of feeling 'as if' one is two people in a single moment, which points instead toward disturbance of self-unity.