Lentis/Dissociative Identity Disorder (Multiple Personality Disorder)
Dissociative Identity Disorder (DID), more commonly known as Multiple Personality Disorder, is characterized by a patient's use of two or more independent and unique personalities that alternate control of the patient, resulting in amnesia beyond forgetfulness. The disorder is not associated with substance abuse (alcohol, etc.) or another general medical condition. There is some debate whether the disorder is genuine or iatrogenic (a result of diagnosis or therapy).
The validity of dissociative identity disorder remains contentious and Drs. McHugh and Putnam were asked to debate the disorders diagnosis. McHugh argues that DID is an artifact of society and not a natural disorder. The contention focuses on patient suggestibility and susceptibility to a psychiatrist’s delving line of questioning. This is best exemplified by Kluft's now discredited initial treatment method focused on detaining patients up to 8 hours to uncover alters .
Putnam contends that DID is real, satisfying all the criteria for a mental disorder: content, criterion-related, and construct validity. Putnam argues that the three primary arguments against DID are incorrect: the iatrogenic diagnosis disproved by the lack of cases due to hypnosis or fascination, hypnosis refuted by the many cases of DID without hypnosis-based treatment, and the media’s effect weakened by the lack of correlation between violence in the media to real-life. Putnam also questions why the same media-driven diagnosis would not be true for other disorders.
There is a strong link between traumatic experiences and dissociative symptoms (Bernstein, 1986 pg 727). Patients suffering from DID tend to be women around the 30 years old, many of whom were abused as children and more so sexually than physically . The link to DID is often rationalized as a coping mechanism, making dissociating the abuse to an alternate personality. The environment appears to cause DID, as the it does not appear be genetically transferred .
Social Factors 
Media Influence 
The media sensationalizes DID as exciting, painful, useful, and perplexing. An early formative showcase of DID was the book Sybil. Sybil is the story of a woman whose psychiatrist, Dr. Cornelia Wilbur, uncovers her history of abuse as a child and her 16 personalities. The story later proves false, as Sybil herself confesses to having made up the personalities. Dr. Wilbur denies her confession, refusing to believe her. As a sign of the inappropriate nature of their relationship, she even left Sybil the profits from her book in her dying will. The story and subsequent movie popularized the image of DID full of complicated and extreme personalities Sybil displayed caused by child abuse. This story formed the first public impression of DID.
Herschel Walker retired from the NFL and discovered he suffers from DID. Because he no longer had football to focus on, alters including the "warrior" on the football field, the "hero" to the media, and a violent personality that threatened to kill both his wife and his therapist on separate occasions revealed themselves. Herschel claims his disorder has positive aspect, and attributes his football success to it. The doubt many have of his disorder reflect a common stigma faced by DID patients.
Nicki Minaj is another celebrity example of "DID". Even though she does not seem to currently suffer from the disorder, she uses different characters in her life and work to gain publicity from the media. In an interview, Nicki mentioned that, growing up in a violent home, she created the character "Cookie", to dissociate the cruel reality. She then created "Barbie",who appeared in her songs and gained popularity among her fans. Both the approval and criticism from the media have brought her increasing publicity, which may contribute to her invention of even more alter egos, such as "Roman Zolanski", who she manipulates to express her rage using foul language and violent acting to enhance the entertainment of her work. The manipulation of alter egos is also seen in other main stream celebrities, such as Lady Gaga, who invented the identity Jo Calderone as her male alter ego.
These examples showed us that performance artists nowadays utilize alternative identities to explore and express their artistic talents and to gain media attention at the same time. Even though their actions have received criticism, the artistic value of their work was not abated. Their followers in the media encourage the behavior by describing it as unique, attractive and impressive. This social influence might have unexpected effects on teens and children of younger age, who are still developing mentally and may be encouraged to develop alternate personalities.
Television and Movies 
Dissociative Identity Disorder has been depicted in the media through avenues such as movies and television shows. The first full television show about a person with DID is United States of Tara. This television show is about a wife and mother who suffers from DID and has 3 main alter personalities. The first alter is a 15 year old wild child named T, then there's Buck a rough outdoors man, and finally Alice who is a classic 1970's housewife. Later seasons introduce more alters. Charmaine, Tara’s sister responds stereotypically to Tara's DID, confronting personalities and asking them to stop, and expressing disbelief of the validity of DID. The producers consulted professionals in the dissociation community, including Dr. Richard Klutz a psychiatrist with almost 40 years diagnosing and treating DID. The show is fairly accurate and incorporates alters with characteristics similar to many patients. However, according to Klutz, “Tara represents only 5% of all D.I.D. patients” because of how over the top she and her alters are. (Kaplan, et. Al, 2009)
Movies such as The Three Faces of Eve (1957),Sybil (1976),Primal Fear (1996), Identity (2003), and Me, Myself & Irene (2000) are prime examples of movies showing DID and the characteristics of people with the disorder. Movies have been very influential on the world's perception of DID and some believe influenced the rise in DID cases.
Technologies and DID 
Hans Berger’s invention of electroencephalogram in 1924 enabled the recording of brain waves. Use of EEG as a diagnostic tool originated from physicians’ surprising discoveries that many patients’ transition between alters involve changes in handedness. Findings that DID may be associated with temporal lobe epilepsy encouraged physicians to use EEG to monitor the activities of the two hemispheres. The results indicate that different alters within an individual would exhibit distinct EEG pattern, which is now a key flag indicating DID.
As previously mentioned, many patients of DID are middle-aged females who were physically or sexually abused as children. Many physicians try to use the results of the EEG studies to correlate physiological disorders with traumatic social experiences. A study suggested that these torturous social experiences may lead to disruption of the organization of dominant hemisphere, which could be a main cause of DID. Over 20 years later, with new technologies (e.g., increased MRI resolution), more tools are being utilized to understand and diagnose DID, including single-photon emission computed tomography(SPECT). Sheehan et al. used SPECT to study the brain activities in the left and right temporal lobes of a potential DID patient and believed that the previously stated hypothesis was never corroborated. They also concluded that ingenuous acceptance of self-reported child abuse without evidence, and failure to finalize the diagnosis of DID prior to treatments may induce iatrogenic aetiology of the disorder. To avoid the possibility of iatrogenic aetiology, neurologists should be aware that EEG readings are not a full-proof diagnostic tool. Sandel et al. discussed that a patient whose EEG reading is negative for DID should only be diagnosed with DID after a longitudinal study of symptoms and the establishment of a therapeutic alliance with the patient.
Fortunately, a previous study demonstrated that the physiologic differences across alters in DID also include differences in response to the same medication, allergic sensitivities, autonomic and endocrine function, and surprisingly, variation in visual functions. Therapists should not rely only on advanced technology when diagnosing DID. Various physiological tests could be taken to accurately diagnose the disorder. Moreover, the use of the internet may also help the diagnosis and treatments of DID. An online blog discussed that a patient explored her life with DID using documented thoughts, songs, poetry, letters to her therapists as well as artwork created during therapy sessions. Unfortunately the blog of that patient was taken down. However, the story show how people are more likely to share and are aware of DID in the 21st century through the internet.
DID is diagnosed using structured interviews, self-report tests, and brief screening self report tests. Corresponding test examples are the Structured Clinical Interview from DSM-IV Dissociative Disorders-Revised(SCI-D-R), the Multidimensional Inventory of Dissociation (MID), and Dissociative Experience Scale (DES). The tests measure how dissociated a patient feels or what symptoms they exhibit. These are initial tests, which are paired with the EEG and other tests before a proper diagnosis.
Self-diagnosis also occurs, and is growing through websites like WebMD, the 81st most visited site in the U.S. with 16 million unique visitors, will likely affect how DID spreads. In a recent case in the United Kingdom, a celebrated individual self-diagnosed his bipolar disorder. His action led to an increase in self-diagnosis or diagnosis from family members.
However DID is commonly misdiagnosed as borderline personality, epilepsy, schizophrenia,somatization disorder, and panic disorder and vice versa because they all demonstrate severe behavioral changes often mistaken as multiple personalities.
There are occasions where people may not have the disorder but believe they do after interaction with a therapist or physician. The sociocognitive model shows iatrogenic and other socialcultural factors being a main reason for the increase in diagnosis of this disorder.  The SCM attributes the diagnosis of DID to factors such as, "… unintentional prompting from therapists, including memories of one's past behavior, observations of other individuals, and media portrayals of DID" . One particular case of iatrogenesis involved a therapist, Dr. Diane Humenansky, which resulted a guilty charge in 1995 for her malpractice. According to Carlson, a former patient of Dr. Humenansky, the therapist provided her with books, talk shows, and videos all depicting DID . During the group therapy sessions some patients started seeing similarities in everyone’s stories and alter’s personalities. After finally dismissing Humenansky, the patients noticed all their experiences were alike and directly reflected the movies and literature they were given. One participant in the group therapy confessed she created an alter named “Nikki” just because everyone else in the group had one. 
There are a safe guards and groups that have been created in order to prevent iatrogenesis. The first is the Hippocratic Oath, which includes a line,"...never do harm to anyone.”  Even though physicians and therapists take this oath, there are outliers like Humenansky who practice unethically for money or fame. Some of the major organizations that are particularly involved in dissociation and its diagnosis are the International Society for the Study of Trauma and Dissociation (ISSTD), Sidran Institute, and the American Iatrogenic Association (AiA).
The goal of any therapy is to help a patient become more functional. Psychiatrists aim to consolidate the personalities. They strive to discuss and accept the abuse that the patient likely suffered. Treatment is generally divided into three phases: Phase 1: Establishing Safety, Stabilization, and Symptom Reduction; 2: Confronting, Working Through, and Integrating Traumatic Memories; and Phase 3: Integration and Rehabilitation.
Stories from media concerning DID in widely-known characters both real and fictional increases the acceptability and attractiveness of DID. Paired with increasing availability of diagnostic information, people are encouraged to self-diagnose and share their ills. However, without tempering from doctors' knowledge and experience, knowledge in the hands on non-professionals risks being mishandled. Patients can superimpose the symptoms of DID on themselves subconsciously to their detriment. A corresponding issue is Global Warming, where non-experts take increased weather extremes and point to where it is getting colder as a sign that global warming is not happening. Knowledge is power, misapplied knowledge is a parasite.
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Useful Links 
For Diagnostic Methods ISSTD Guidelines for Treating DID