Introduction:

Dissociative disorders are characterized by impaired conscious integration functions, personal identity, memory and environment perception. Their frequent psychopathological manifestations are amnesia, depersonalization, fugue states, extra sensorial experiences, trance states and total personality changes.

They usually appear under different life stressors, and their clinical course is highly variable. Prevalence estimates give figures ranging from 5 to 10% among general population, and reach 10.2 to 41.4% among psychiatric populations. This wide variation is one of the indicators of the complexity of this diagnostic entities and of its difficulty to be studied. Culture is a key factor in functionality of subjects with a dissociative disorder, because the acceptance of many of its clinical features varies.

It is accepted that these diagnostic categories are barely-recognized, not only by general physicians, but by experienced mental health specialists.

The original Structured Diagnostic Interviews (SCID, CIDI, SADS, SCAN), did not include them in their widely distributed packages, and many of them decided to create a separate appendix to address them. Unfortunately, structured interviews face an important limitation as there is a lack of trained, and some times, experienced psychopathologist, a fact that difficults to use them in large samples.

Self-report instruments, when they show good reliability and validity, are of great value in terms of time, costs and feasibility. Their major limitation is the low reliability that they show in psychiatric conditions in which lack of insight is present (psychotic disorders).

To evaluate the psychometric properties of translated versions of instruments is highly desirable. This is specially important when elusive disorders are being evaluated.

Given that the cultural environment of Mexico is surrounded by several factors that influence this kind of disorders, the availability of reproducible research instruments is of outmost relevance.

Therefore, the Dissociative Experiences Scale (DES) -the most widely used measure in this field- in contrast with the Dissociative Disorders Interview Schedule (DDIS), was evaluated, with the purpose to give a first approach to a 12 month prevalence of some Dissociative disorders in Mexican psychiatric patients.

Methods:

Subjects:

A non-random, consecutive sample of male and female patients, between 18 and 63 years old were included. They were receiving treatment, regardless of the diagnosis, at the Institute of Mental Health of Jalisco, from the State's Ministry of the Health in Mexico. The ethics committee authorized the study, and they all gave informed consent.

Translation:

The Spanish version of the DES, has a Spanish translation, and a Mexican Spanish idiomatic adaptation was performed by consensus. The DDIS was translated by one bilingual psychiatrist, and independently reviewed by another. Consensus was reached in controverted items. Once a final translated version was obtained, it was given to 10 subjects (mainly with primary school level), to assess item understanding. A second review was performed to reach a culturally compatible version, concentrating in respecting item content validity. Back translation was not considered, because this method does not capture common language of low school population, which is the case of most Mexicans.

Measures:

Dissociative Experiences Scale (DES):

This is a 28 items, self-report scale, designed to evaluate different kinds and severity of Dissociative conditions, in a 0 to 100 range. Most populations without a psychiatric condition or with a non-Dissociative disorder, scored under 20. A cut-off point of 30, usually indicates the possibility of a Dissociative disorder diagnosis. Given that a Spanish version of the DES is available from Spain, only an idiomatic adaptation to Mexican Spanish was performed (changes in slang or word content differences between countries).

Dissociative Disorder Interview Scale (DDIS):

This is a structured diagnostic interview, of 132 yes/no items, designed to assess the presence of DSM-IV Dissociative disorders entities. It is to be applied by mental health professionals, properly trained on its use. It does not give a total score, it assesses each disorder independently. As previous studies performed in different languages, it has adequate psychometric properties, and is the usual golden standard for Dissociative categories. Previous reports on DDIS correlation with DES have shown variations between disorders, with Kappa values for Identity Dissociative Disorder ranging 0.68 to 0.95.

Procedures:

A 4th year general psychiatry residency doctor was trained in the DDIS, and, after obtaining the patient's consent, applied the DDIS interview, and then gave the patient the DES to be completed. Demographic and clinical variables were obtained, as well as the diagnosis assigned in the patient chart. To analyze results two procedures were planned: 1) compare DES total score punctuation between positive and negative presence of Dissociative disorders according with the DDIS and 2)compare between patients with a Dissociative disorder with or without concomitant major depression.

Results:

A total of 100 subjects were included, 63% female, with a mean age of 32.4±12.5 (range 18 - 63) years old. The DES internal consistency index was 0.96. Patients with a Dissociative Disorder (according to the DDIS), showed clinically and significantly higher DES values than non-Dissociative patients (34.7±24.8 n= 38 vs. 10.7±9.6 n=62; T -6.8, d.f. 98, p< 0.001).

Frequency of Dissociative disorders and symptoms:

Mean DES total score was 19.8±20.6. According to DDIS criteria, 38 subjects fulfilled DSM IV diagnostic criteria for a Dissociative disorder: Dissociative identity disorder 24, Depersonalization Disorder 6, psychogenic fugue 3.

The most common concomitant diagnosis as assessed in the patient chart was unipolar major depression (17 44.7%. When a Dissociative disorder was comorbid with major depression, comparing it with Dissociative disorders only, the difference was greater (34.7±24.2 n= 38, 9.3±8.55, T 6.3, d.f. 80, p<000.1.

Discussion:

Dissociative disorder measurements evaluated, seem to work adequately in Mexican population. Prevalence of dissociative disorders found in this psychiatric population, is consistent with other studies. Further research in the field is needed, to evaluate the influence of cultural factors, including rural and indigenous samples.

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