Dissociative Identity Disorder in Psychiatric Inpatients

In recent years reports have appeared suggesting that dissociative identity disorder is common, and there is concern that it is misdiagnosed as schizophrenia, borderline personality disorder, or major depression (1). Bliss and Jeppsen (2), using a self-report form with inpatients, diagnosed eight patients (seven women and one man) as having dissociative identity disorder by DSM-III criteria. They reported a rate of dissociative identity disorder of 13% assuming that the 20% who did not return the report did not have dissociative identity disorder, or 16% excluding those subjects.

Ross et al. (3) studied patients admitted to two 23-bed psychiatric inpatient units at a university teaching hospital. For unstated reasons, they excluded patients entering with a diagnosis of dissociative identity disorder. Of 484 subjects, 62% completed the initial screening instrument, the Dissociative Experiences Scale (4). Of these subjects, 90 (30%) scored 20 or higher and were asked to complete the Dissociative Disorders Interview Schedule (5); of those patients, 80 were interviewed. Ross et al. found that 10 received a diagnosis of dissociative identity disorder. Another clinician interviewed these subjects and found that 16 had dissociative identity disorder, i.e., 10 who had dissociative identity disorder on the Dissociative Disorders Interview Schedule, three who had a different diagnosis on the Dissociative Disorders Interview Schedule, and three who other clinicians considered to have dissociative identity disorder. Ross et al. concluded that the occurrence of dissociative identity disorder was between 3.3% (those who received the diagnosis on both the Dissociative Disorders Interview Schedule and the clinical interview) and 5.4% (those who received the diagnosis from a clinical diagnosis). This study illustrates the difficulty in ascertaining the diagnosis of dissociative identity disorder through rating instruments.

Carlson et al. (6), in a study designed to validate the Dissociative Experiences Scale, interviewed a large sample, 1,051 subjects, but they were not a representative sample of inpatients and could not provide data on the occurrence of dissociative identity disorder. Saxe et al. (7) asked 171 patients who were consecutively admitted to a state psychiatric hospital to complete the Dissociative Experiences Scale; 110 patients (64%) complied. Of the 17 who scored above 25, Saxe et al. interviewed 15 with the Dissociative Disorders Interview Schedule; four patients (3.6%) received the diagnosis of dissociative identity disorder. Latz et al. (8) surveyed all women ages 18–65 years who were admitted to a state hospital. Of 421 subjects considered for the study, they interviewed 176 (42%) with the Dissociative Experiences Scale and the Dissociative Disorders Interview Schedule. They found that 21 (12%) had dissociative identity disorder.

Horen et al. (9) screened 48 male and female inpatients of 192 eligible subjects (27% of women and 24% of men). Of the 14 who scored higher than 24 on the Dissociative Experiences Scale, Horen et al. interviewed nine with the Dissociative Disorders Interview Schedule and the Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D). Of these, three received diagnoses of dissociative identity disorder on both instruments, and one was given a diagnosis of dissociative identity disorder on the Dissociative Disorders Interview Schedule but a diagnosis of dissociative disorder not otherwise specified on the SCID-D. Horen et al. did not report the sex of those diagnosed with dissociative identity disorder but gave a rate for dissociative identity disorder of 6% (N=3 of 48). They described much difficulty in using the self-administered Dissociative Experiences Scale as the screening instrument because patients often seemed not to understand the questions or gave contradictory answers. The 48 subjects differed significantly from the 192 eligible subjects on several measures: more subjects in the former group were women, the subjects were more likely to have remained married, had more education, and were less likely to have schizophrenia. The treating psychiatrists gave permission to the researchers to interview only 58% of eligible patients, a further source of bias.

We studied a random sample of women by using what we believe to be more accurate methods than those in the preceding studies.

METHOD

We conducted this study between July 1996 and February 1997 at the Hillside Hospital Division of Long Island Jewish Medical Center in Queens, N.Y. Hillside Hospital, a teaching hospital, serves mainly Queens and Long Island. Almost all inpatients come from the local area. We randomly selected female subjects between the ages of 16 and 50 years, choosing this group because dissociative identity disorder occurs most frequently in this age range. We excluded patients receiving ECT because the treatment might interfere with subjects' ability to provide accurate information. Third- and fourth-year psychiatric residents conducted the initial interviews with the SCID-D (10) between the fifth and 10th days of hospitalization. If a subject refused to cooperate or appeared too symptomatic to reasonably provide information, the rater returned a few days later to determine if the interview seemed feasible. Raters discussed the subject with ward staff to obtain the description, if any, of different personalities.

Over 50% of all initial interviews were done by one rater (D.G.). If the initial interview with the SCID-D indicated definite or probable dissociative identity disorder, a senior clinician (A.R.) interviewed the subject again with the SCID-D.

The SCID-D contains questions about the symptoms required by DSM-IV for dissociative identity disorder. We consider this a more direct means of ascertaining the diagnosis than using rating scales or an interview schedule that is not clearly pegged to the DSM-IV criteria and leaves no room for inquiry. The SCID-D not only provides questions for all relevant symptoms for dissociative identity disorder and other dissociative disorders, but, as a semistructured interview schedule, it also requires the interviewer to expand on the suggested wording of a question, as a clinician would do during a standard diagnostic interview. The SCID-D assesses not only the presence of symptoms, but also the degree of distress and cause of functional impairment, which are requirements necessary for assigning the diagnosis. The SCID-D is a guide to a clinical interview, not a rating scale. We believe the accuracy of our diagnoses comes from 1) the assurance that in following the SCID-D we have not omitted any relevant questions and have considered all criteria necessary for the diagnosis; and 2) our clinical skills in conducting the interview. We hope this provides the closest to a “gold standard” for diagnosis: two interviews, one by an experienced clinician, using a semistructured interview guide. Previous studies of the prevalence of dissociative identity disorder in inpatients did not use this procedure.

We made no attempt to establish a diagnosis other than a dissociative disorder. The interviewers read the subject's chart before the interview and knew the working diagnosis and clinical information about the subject. The interviewers carefully looked for symptoms of psychosis, mood disorders, anxiety disorder, or cognitive impairment that might resemble symptoms of dissociation. After complete description of the study to the subjects, written informed consent was obtained.

RESULTS

We interviewed 100 subjects (63%) of 158 approached. We could not interview 58 subjects for the following reasons: 30 patients were discharged before the fifth day, nine were too psychotic to be interviewed, nine refused, nine could not be interviewed for administrative reasons, and one patient was transferred to a medical ward. We found one subject (1%) with dissociative identity disorder. Both interviewers concurred in the diagnosis.

DISCUSSION

By having two clinicians use a semistructured interview guide, rather than a self-rating screening instrument or a fixed-question scale, we think our methodology most closely approaches the gold standard of diagnosis. Our finding of a 1% occurrence rate is lower than what previous research found. We attribute this to our improved methodology, but further research should answer the question more definitively.

The major limitation of this study is that we could not interview 37% of the subjects. Even if a substantial proportion of these subjects had dissociative identity disorder, we would still not approach the figures reported elsewhere, such as 12% by Latz et al. (8). We found that dissociative identity disorder rarely occurred among a randomly selected sample of female psychiatric inpatients. This conclusion should be softened by the fact that other investigators have found a higher rate. Clearly, more studies are needed.

Received June 12, 1997; revision received Oct. 27, 1997; accepted Dec. 22, 1997. From Hillside Hospital Division of Long Island Jewish Medical Center. Address reprint requests to Dr. Rifkin, Hillside Hospital, Glen Oaks, NY 11004.