PREVALENCE OF DISSOCIATIVE SYMPTOMS AND DISORDERS WITHIN AN ADULT OUTPATIENT POPULATION WITH SCHIZOPHRENIA

Objective: The objectives of this study were to determine the prevalence of dissociative symptoms and disorders in an adult outpatient population with schizophrenia and to study the relationship between dissociative symptoms and positive and negative symptoms of schizophrenia. Method: Consenting adult outpatients with schizophrenia from the Kingston Psychiatric Hospital in Kingston, Ontario, were administered the Dissociative Experiences Scale (DES). Patients scoring 25 or higher on the DES were interviewed with the Positive and Negative Syndrome Scale (PANSS), and two interviews for dissociative disorders: the Structured Clinical Interview for DSM-1V Dissociative Disorders (SLID-D) and the Dissociative Disorders Interview Schedule (DDIS). Results: 53 patients completed the DES, and 14 (26%) . scored 25 or greater. The scores on the DES subscale of absorption and imaginative involvement were significantly higher than the scores of the two other DES subscales, for both the group scoring >25 and also for the study sample as a whole. The prevalence of dissociative disorders in this population was estimated to be 9%, with dissociative amnesia the only dissociative disorder diagnosed. The high DES scorers had a predominance ofpositive symptoms as evidenced by a composite index score (positive symptoms score minus negative symptoms score) of 4. 1, placing these patients at the 80th percentile, when compared to a normative population of patients with schizophrenia. Conclusions: The finding of consistently elevated scores on the absorption and imaginative involvement subscale of the DES in this sample suggests that the DES may not be a valid instrument to screen for dissociative disorders among patients with schizophrenia. However, patients with schizophrenia who present with a predominance of positive symptoms should be assessed for the presence of a dissociative disorder. INTRODUCTION Dissociative disorders are being recognized as increasingly significant psychiatric conditions (Ross, Anderson, Fleisher, & Norton, 1991; Saxe etal.,1993; Horen, Leichner, & Lawson, 1995; Ellason, Ross, Mayran, & Sainton, 1994). Not only is the primary diagnosis of dissociative disorders escalating, these disorders are also present as a comorbid condition in as many as 15-20% of adult psychiatric inpatients (Ross et al., 1991; Saxe et al., 1993; Horen et al., 1995) . However, with many patients receiving numerous different diagnoses prior to the recognition of a dissociative disorder, the diagnosis of dissociative disorders is often overlooked or significantly delayed (Saxe et al., 1993; Steinberg & Steinberg, 1994). Diagnosis of these conditions is complicated by the tendency for patients to present with symptoms which resemble other disorders, notably schizophrenia ( Ross et al., 1991; Saxe et al., 1993; Steinberg, Rounsaville, & Cicchetti, 1990). Patients with schizophrenia and those with a dissociative disorder such as dissociative identity disorder (DID formerly multiple personality disorder) tend to present with Schneiderian first-rank symptoms. This leads to between 26-49% of DID patients receiving a prior diagnosis of schizophrenia (Gainer, 1994). Schneiderian first-rank symptoms include delusions, auditory hallucinations, thought insertion/withdrawal, and feelings of external control of one's thoughts, feelings or actions. Recent evidence has shown that the dissociative population may endorse these symptoms to a greater extent than do schizophrenics (Ellason & Ross, 1995). In a study by Ross et al. (1990), 1'739 schizophrenic patients possessed an average of 1.3 Schneiderian symptoms each, whereas 368 patients with dissociative identity disorder acknowledged an average of 4.9 of these symptoms (Ellason & Ross, 1995). A recently published study, which examined the prevalence of dissociative disorders in a Canadian adult psychiatric inpatient population, found that 29% of patients possessed dissociative psychopathology, and an estimated 17% of the patients had a diagnosable dissociative disorder based on clinical interview criteria (Horen et al., 1995). However, a major problem with diagnosing dissociative disorders in schizophrenic inpatients was noted because these patients were often too symptomatic to be assessed proper-