Epidemiology and Comorbidity of DID

Dissociative Identity Disorder
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An artist's interpretation of dissociative identity disorder

Dissociative identity disorder (DID) is a mental disorder characterized by multiple persisting personalities or identities that emerge at different times to alter the person's behavior. Unfortunately, the high degree of comorbidity of DID with other various mental disorders such as post-traumatic stress disorder, major depression, obsessive compulsive disorder, and somatoform disorder makes proper diagnosis of DID is extremely difficult. [1]. As a result, patients are commonly misdiagnosed with schizophrenia due to common symptoms [1]. The prevalence of DID seems to heavily favor females over males according to several US studies performed in the last two decades [2]. In addition, clinical populations of psychiatric patients all seem to have varying levels of DID incidence depending on the country [3]. Distinct cultural backgrounds seem to have a strong influences on the diagnosis of DID, as countries perform different diagnostic tests and interpret symptoms in inconsistent manners [4].

1 Diagnostic Testing

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Prevalence of dissociative disorders conducted by various studies using DDIS and SCID-D methods.

1.1 DDIS vs SCID-D

Due to basic psychiatric assessments such as the Structured Clinical Interview for DSM-IV (SCID) being unable to cover dissociative disorders, DID is commonly misdiagnosed early in prognosis; as a result, conducted large-scale epidemiological studies have previously produced biased data [3,5]. Shortly following the release of SCID, a protocol known as SCID-D was published in an attempt to regulate the screening of dissociative disorders [3,6]. In addition, an alternative diagnostic tool known as the Dissociative Disorders Interview Schedule (DDIS) was also released and is globally utilized to test for dissociative disorders. However, studies have shown that diagnosis of DID through SCID-D results in lower prevalence rates than diagnosis through DDIS [4]. Both the SCID-D and the DDIS are taken in interview form and vary in length between 30 to 90 minutes depending on the subject's experiences [7,8].

1.2 DES

In order to compensate for the length of time it requires to complete a DDIS or SCID-D interview, the Dissociative Experiences Scale (DES) was created to function as a simple questionnaire to determine high dissociation patients within a clinical population [15]. In a screening process, subjects would undergo the DES and were followed up with SCID-D or DDIS interviews if the DES scores hit a minimum threshold [15].

2 Prevalence

2.1 General Population

There are very few published studies and data on dissociative identity disorder due to low incidence rates worldwide [9]. It is more commonly diagnosed in young adults relative to older adults. [9]. In addition, females are nine times more likely to develop DID than their male counterparts [2]. However, this gender bias may be accounted for by the fact that males afflicted with DID are occasionally diagnosed subsequent to committing a crime and therefore find themselves behind bars rather than in a psychiatric hospital, thereby seemingly inflating the female sample size with DID diagnoses [10]. Further support came in the form of two studies performed in Germany in 2003 and Finland in 2007 where researchers were unable to find significant gender bias in dissociative disorder populations [3].

According to a study performed in 1984, the prevalence of DID in the general population was estimated to be between 0.01 to 1% [11]. Recent studies have shed more light on incidence rates in the community and increased numbers to 1-3% [12]. Various theories have been constructed to explain the rise of DID which includes the psychiatrists' previous inability to recognize DID and therapists' suggestions influencing the diagnostic tests performed [13].

2.2 Clinical Population

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Methodologies in dissociative disorder and DID prevalence studies in clinical populations.

The prevalence rates of DID in clinical populations have a high variance rate worldwide ranging between 0.5% to 12% depending on the country in which the study was performed [3,4]. Multiple studies in North America have presented higher prevalence rates with respect to the rest of the world [9] with incidence rates reaching up to 5.4% [14]. Initially, the majority of DID studies were generated within the United States; therefore, the longevity of DID diagnosis in the western hemisphere may have resulted in increased incidence rates [14].

2.3 Friedl, Draijier, and de Jonge (2000)

In a meta-analysis study conducted by Friedl, Draijier, and de Jonge, all DID prevalence studies between the period of December 1991 to January 2000 were investigated in order to determine the reason behind the high variance (approximately 10-fold) in prevalence rates on an international level [4]. Upon the examination of over 1300 psychiatric patients, the authors approximated a clinical population prevalence rate of 19% for dissociative disorders and a 4.4% for DID in particular [4]. In conclusion, Friedl and colleagues discuss two major factors responsible for the disparity between countries. Firstly, the diagnostic tool utilized to measure dissociation was a critical factor [4]. They suggest that the format of the DDIS is not as refined relative to the SCID-D in evaluating dissociative symptoms; therefore, the DDIS is less likely to catch factitious disorders and would be skewed towards a misdiagnosis [4]. Ultimately, the authors favor the SCID-D diagnostic instrument because of its lack of closed questions and suggestibility [4]. The second factor responsible is the notable influence of the cultural differences of each country performing DID studies in interpretation of dissociation symptoms [4]. Certain cultures are more heavily inclined to dismiss or deem negligible certain symptoms than others [4].

3 Comorbidity

Patients diagnosed with DID are commonly diagnosed with an average of five to seven additional comorbid disorders including post-traumatic stress disorder (PTSD), borderline-personality disorder, anxiety disorders, Asperger's syndrome, mood disorders, epilepsy, and somatoform disorder [9]. In order to differentiate DID from other disorders, the therapist or psychiatrist should be able to recognize the presence of persisting personalities, amnesia, and other standard DID symptoms. However, certain precautions must be taken to properly diagnose DID. For example, patients may have malingering or factitious disorder and are merely faking DID symptoms for secondary gain. Patients faking DID will often present DID symptoms excessively yet are seemingly not stressed about their particular predicaments. As a result, it has been suggested that DID is not being diagnosed appropriately enough due to psychiatrists' and therapists' suspicions regarding the authenticity of the dissociation symptoms.

3.1 Schizophrenia

Patients diagnosed with DID are commonly previously misdiagnosed with schizophrenia due to a large overlapping of symptoms known as Schneiderian symptoms [16]. Schneiderian symptoms can generally be categorized into positive and negative symptoms [17]. Positive symptoms are defined as those which schizophrenic patients experience but are absent in normal people including hallucinations [17]. Negative symptoms are composed of a decreased function of normal emotional responses such as motivation and forming interpersonal relationships [17]. Patients with DID often show positive Schneiderian symptoms but lack negative symptoms. [16]. Furthermore, DID patients will attribute auditory hallucinations as internal, rather than external as schizophrenic patients do [10].

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