Dissociative identity disorder, formerly called multiple personality disorder, is a type of dissociative disorder characterized by ≥ 2 personality states (also called alters, self-states, or identities) that alternate. The disorder includes inability to recall everyday events, important personal information, and/or traumatic or stressful events, all of which would not typically be lost with ordinary forgetting. The cause is almost invariably overwhelming childhood trauma. Diagnosis is based on history, sometimes with hypnosis or drug-facilitated interviews. Treatment is long-term psychotherapy, sometimes with drug therapy for comorbid depression and/or anxiety.
(See also Overview of Dissociative Disorders.)
How overt the different identities are varies. They tend to be more overt when people are under extreme stress. The fragmentation of identity usually leads to asymmetric amnesia, in which what is known by one identity may or may not be known by another; ie, one identity may have amnesia for events experienced by other identities. Some identities appear to know and interact with others in an elaborate inner world, and some identities interact more than others.
In one small US community study, the 12-month prevalence of dissociative identity disorder was 1.5%, with men and women affected almost equally (1). The disorder may begin at any age, from early childhood to late life.
Dissociative identity disorder has the following forms:
Possession
Nonpossession
In the possession form, the identities usually manifest as though they were outside agents, typically a supernatural being or spirit (but sometimes another person), who has taken control of the person, causing the person to speak and act in a very different way. In such cases, the different identities are very overt (readily noticed by others). In many cultures, similar possession states are a normal part of cultural or spiritual practice and are not considered dissociative identity disorder. The possession form that occurs in dissociative identity disorder differs in that the alternate identity is unwanted and occurs involuntarily, it causes substantial distress and impairment, and it manifests in times and places that violate cultural and/or religious norms.
Nonpossession forms tend to be less overt. People may feel a sudden alteration in their sense of self or identity, perhaps feeling as though they were observers of their own speech, emotions, and actions, rather than the agent. Many also have recurrent dissociative amnesia.
