Dissociative identity disorder
Dissociative identity disorder (DID) is defined in the DSM-IV-TR as the presence of two or more personality states or distinct identities that repeatedly take control of a patient's behavior, so that the patient has an inability to recall selected memories or personal information. In dissociative identity disorders, the lack of recall is too great to be explained by normal forgetfulness, and is more complete and total than any type of role-specific memories. To fit the diagnosis, the disorder also cannot be due to the direct physical effects of a general medical condition or substance.
The National Library of Medicine's Medical Subject Headings (MeSH) browser also accepts this condition as a recognized illness, under the name multiple personality disorder; a literature search in some medical databases may prefer the latter term. The idea of multiple personalities arises from the tendency for patients with dissociative identity disorders to claim different names and to display different (sometimes radically different) modes of behavior and other facets of personality and identity consistently associated with those names.
The etiology of DID is believed to entail a failure to integrate certain aspects of memory, conscious awareness and identity. Patients experience frequent gaps in their memory (often reported as "blackouts") for their personal history, past and present. Patients with DID also typically report histories of severe physical and sexual abuse, especially during childhood; reports that are frequently validated by objective evidence.
Physical evidence may include systematic variations in physiological functions associated with different identity states, including differences in vision, levels of pain tolerance, symptoms of somatic conditions such as asthma, the response of blood glucose to insulin and sensitivity to allergens. Other physical findings may include scars from physical abuse or self-inflicted injuries, headaches or migraines, asthma and irritable bowel syndrome. DID has been found in a variety of cultures around the world. It is diagnosed three to nine times more often in adult females than males, and female patients also report more identities. Females average 15 or more identities, while males average eight identities.
The average time period from the first presentation of DID symptoms to its diagnosis is six to seven years. DID is associated to some extent with young adult patients. It may become less manifest as patients reach past their late 40’s, but in such cases it can reemerge during stress, trauma or substance abuse. Several studies have suggested that DID is more likely to occur among first-degree biological relatives of people who already have DID, than in the regular population.
Though the majority of scientific studies have found dissociative identity disorder to be a legitimate condition, there has been ongoing controversy as to its origins and inclusion in the DSM and National Library of Medicine classification.
Individuals diagnosed with DID demonstrate a variety of symptoms with wide fluctuations over time. Functioning can vary from severe impairment in daily functioning to normal or even high abilities. Patients may experience an extremely broad array of other symptoms that resemble epilepsy, schizophrenia, anxiety disorders, mood disorders, post traumatic stress disorder, personality disorders, and eating disorders.
The causes of dissociative identity disorder are theoretically linked with the interaction of overwhelming stress, traumatic antecedents, insufficient childhood nurturing, and an innate ability to dissociate memories or experiences from consciousness. Prolonged child abuse is frequently a factor, with a very high percentage of patients reporting documented abuse often confirmed by objective evidence. The Diagnostic and Statistical Manual of Mental Disorders states that patients with DID often report having a history of severe physical and sexual abuse. The reports of patients suffering from DID are "often confirmed by objective evidence," and the DSM notes that the abusers in those situations may be inclined to "deny or distort” these acts. The DSM also states that "controversy surrounds the accuracy" of the reports of child abuse, because childhood memories can possibly be distorted and some sufferers of this disorder are "highly hypnotizable and especially vulnerable to suggestive influences."  Research has shown that DID is characterized by reports of extensive childhood trauma, usually child abuse. Dissociation is recognized as a symptomatic presentation in response to psychological trauma, extreme emotional stress, and in association with emotional dysregulation and borderline personality disorder. Some consider it a culture bound and iatrogenic syndrome  while others contest this idea 
There have been dramatic increases in reported cases of DID in the United States in recent years. The DSM-IV-TR states that the sharp rise in reported cases has been given a range of different interpretations. Some believe that specification of the conditions combined with the greater awareness of the diagnosis among those in the mental health field have caused the identification of cases that previously woud not have been diagnosed. Others believe that the condition has been over-diagnosed among those that are highly suggestible.  Others have claimed that individuals suffering from DID were previously misdiagnosed. 
DID meets all of the guidelines for inclusion in the DSM and is supported by taxometric research. Research has established DID as a valid diagnosis. In one study, DID was found to be a genuine disorder with a constant set of core features.
The 19th century saw a number of reported cases of multiple personalities which Rieber estimated would be close to 100.
By the late 19th century there was a general realization that emotionally traumatic experiences could cause long-term disorders which may manifest with a variety of symptoms. Between 1880 and 1920, many great international medical conferences devoted a lot of time to sessions on dissociation. Starting in about 1927, there was a large increase in the number of reported cases of schizophrenia, which was matched by an equally large decrease in the number of multiple personality reports. Bleuler also included multiple personality in his category of schizophrenia. It was found in the 1980s that MPD patients are often misdiagnosed as suffering from schizophrenia. Multiple personality disorder began to emerge as a separate disorder in the 1970s when an initially small number of clinicians worked to re-establish MPD as a legitimate diagnosis.
Popular awareness of the condition of "multiple personalities" rose dramatically after publicity surrounding a book and movie dealing with the case of "Sybil", since identified as Shirley Ardell Mason (1923-1998) from a small town in Minnesota, whose 13-16 distinct identities were identified in psychotherapy with Flora Rheta Schreiber while she was a student at Columbia University. Herbert Siegel, a psychiatrist who also saw Mason as a patient disputed Schreiber's diagnosis and characterized Mason as "an extremely suggestible hysteric."  The circumstances that led Schreiber to go public with the case, and Dr. Siegel to also go public with his skepticism added significantly to the controversy surrounding this diagnosis. However, Dr. Leah Dickstein, whose mentor was Dr. Wilbur  also stated that she was in touch with Mason for many years after Wilbur died. She remembers Mason telling her that "every word in the book is true." She stated that Wilbur had "no need to make this up." (Note: There is much more controversy about whether or not the condition actually exists in the general public than among mental health researchers and therapists, as the evidence cited here indicates.)
Some skeptical of the diagnosis have stated that the DID diagnosis is not a reliable one and that the arguments to support the concept are illogical. Some have critiqued the DID diagnosis, stating that it was found primarily in the United States and is a cultural construct., yet more recent research has shown different diagnostic rates in other parts of the world. Others have stated that the research on DID does not support the ideas that DID is a construct of either psychotherapy or the media or they have critiqued those skeptical of the DID diagnosis and theories of iatrogenesis and social construct. One researcher states that the evidence backing the traumatic origins of DID is "plagued by poor methodology." , however the DSM states that DID sufferers have "past histories of sexual or physical abuse (that) are confirmed by objective evidence." 
Forensic aspects of DID
The book Forensic aspects of dissociative identity disorder looks at the role of crime in the lives of people that suffer from Dissociative Identity Disorder. It is a collection of essays written by several international researchers. It explores the legal, moral, ethical and clinical questions that psychotherapists and other professionals face while working with those suffering from Dissociative Identity Disorder. Authors that have contributed to the book come from the fields of psychotherapy, counselling, psychology, medicine, law, police, psychoanalysis and social work. Chapters include discussions on ritual abuse, dissociative identity disorder, mind control, extreme abuse, survivor accounts and criminal convictions.
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