DID is widely under-reported and under-recognized. My estimation of prevalence based on my own epidemiological data and according to the DSM-5 diagnostic criteria is around 2.9 % among women in the general population. This figure is above those based on the DSM-IV criteria (i.e. 1.0-1.5%) which were narrower compared to those in the DSM-5. The main differences between DSM-IV and DSM-5 criteria are in the coverage of experiences of possession as a cultural variant and that switching between personality states is not necessarily to be observed but being reported is sufficient in the latter. Previously, such cases were considered as other specified dissociative disorders (i.e. partial or subthreshold DID). In clinical psychiatric settings, these rates rise to 2-3% (for general psychiatric outpatient units) and to 5% (for general psychiatric inpatient units). A North American community study revealed no significant difference in the prevalences between genders. Nevertheless, studies show that women with DID are overrepresented in clinical settings compared to the community and the prevalence is higher among adolescents and high-risk populations such as those with chemical dependency.

This is another domain that is understudied yet. In particular, an increasing number of adolescents present with concurrent gender dysphoria and DID nowadays. Alternate personalities carrying identities of opposite genders are common both among female and male patients with DID. Principally, treatment of DID may be necessary until the issue about gender dysphoria is fully clarified.

The prognosis for clients with DID is variable. Overall, compared to several other psychiatric disorders, the outcome can be positive even in terms of achieving “normalcy”. The prognosis depends both on patient and therapist characteristics and the quality of the relationship and communication between them. Anyway, the first stage of the treatment is always targeted at achieving stability. This may require the treatment of depression, “borderline” phenomena, experiences of possession, and brief psychotic attacks. Dealing with anger and affect dysregulation is essential. Self-mutilation and suicidality and functional neurological symptoms may require urgent crisis intervention and differential diagnosis of medical emergencies for the latter. The patient should be informed about the possibility of a fully positive outcome in condition that both parties (i.e. the patient and the therapist) are able to work toward this direction successfully. However, as indicated for any psychotherapy, this cannot be guaranteed beforehand and any progress toward healing which both parties regard as such may be accepted as an improvement.

The best treatment for DID is integrative psychotherapy. For a subgroup of patients, a rational general psychiatric intervention is also required including pharmaco-therapeutic measures. Integrative psychotherapy means a generically “good” treatment taking into account the patient’s individual needs rather than strict dependence on a certain type or technique of psychotherapy. Issues of attachment, post-traumatic symptoms and cognitions, alleviation of emotion dysregulation and anger, interpersonal boundary management are parts of any psychotherapy of DID. Pacing the interventions while pursuing the “window of tolerance of emotions” is essential to prevent daily attacks of crisis which are usually constituted of flashbacks, disturbances of sense of agency, anxiety, and frequent experiences of switching. Such treatment is usually referred to as phase oriented trauma therapy which combines insights of psycho-traumatology with consideration of psychodynamic principles of psychotherapy.

Full integration can be achieved by a subgroup of patients while some of them remain stuck in the position of partial co-consciousness.

Being informed about the nature of the psychopathology is essential both for the affected individual and his or her close circle of related people including family members. However, this should never lead to exceeding the interpersonal boundaries and development of intrusive attitudes toward the individual with DID. The patient should be regarded as “one person” rather than someone with “multiple personalities”, however, his or her difficulty in controlling switching between personalities should be accepted as it is until a better level of integration is achieved. One should never forget that any individual with “multiple personalities” struggles for integration at the same time and alternate personalities try to contact people as regarding itself as a unitary person rather than a member of a group.

Scientific research has not achieved definitive results answering whether BPD and DID are phenomena related to the same psychopathology or whether they are really different entities. Principally, one can never be sure until healing of DID whether BPD was involved or not because DID itself lead to “borderline” phenomena anyway as a consequence of the psychological fragmentation. My research suggests that BPD and DID overlap to a large extent in clinical phenomenology; i.e. they both represent chronic/trait response to developmental traumatization while presence of acute/state dissociation is sometimes more important than this distinction. Namely, acute dissociation and repetitive crisis episodes may lead to re-enactments and revictimization. Such attacks may occur both in BPD-like or DID-like conditions. Again, my research shows that awareness about childhood traumatization influences the ways of coping to a large extent that diminished awareness leads to re-enactments and crises more frequently, while awareness triggers identity alterations and depersonalization-derealization. Interestingly, patients with DID are less aware of their amnesias. This leads to the conclusion that BPD-like patients are composed of co-conscious and/or co-present alternate personalities more readily. The final diagnosis also depends on the full awareness of the clinician about his or her patient’s condition. As a general principle, those with BPD tend to act their experiences in an interpersonal arena more readily (e.g. by an experience of projective identification) than issues of boundary pop up more frequently and requires to be managed.