The Cambridge Depersonalisation Scale: a new instrument for the measurement of depersonalisation

Abstract

Existing self-rating scales to measure depersonalisation either show dubious face validity or fail to address the phenomenological complexity of depersonalisation. Based on a comprehensive study of the phenomenology of this condition, a new self-rating depersonalisation questionnaire was constructed. The Cambridge Depersonalisation Scale is meant to capture the frequency and duration of depersonalisation symptoms over the ‘last 6 months’. It has been tested on a sample of 35 patients with DSM-IV depersonalisation disorder, 22 with anxiety disorders, and 20 with temporal lobe epilepsy. Scores were compared against clinical diagnoses (gold standard) and correlated with the depersonalisation subscale of the Dissociation Experiences Scale (DES). The scale was able to differentiate patients with DSM-IV depersonalisation disorder from the other groups, and showed specific correlations with the depersonalisation subscale of the DES (r=0.80; P=0.0007). The scale also showed high internal consistency and good reliability (Cronbach alpha and split-half reliability were 0.89 and 0.92, respectively). The instrument can, therefore, be considered as valid and reliable, and can be profitably used in both clinical and neurobiological research.

Introduction

A clinical phenomenon often met with in psychiatric and neurological practice, depersonalisation has been associated with a variety of neuropsychiatric conditions such as anxiety disorders, migraine and epilepsy. It can also be a disorder in its own right, and when so it tends to run a chronic course (Simeon et al., 1997). DSM-IV defines depersonalisation as: ‘an alteration in the perception or experience of the self so that one feels detached from, and as if one is an outside observer of, one’s mental processes or body (e.g. feeling as if one is in a dream)’; and derealisation as ‘an alteration in the perception or experience of the external world so that it seems strange or unreal (e.g. people may seem unfamiliar or mechanical)’, respectively (American Psychiatric Association, 1994). In this article, ‘depersonalisation’ will be used as a generic term encompassing both phenomena as there is not conclusive evidence that they are independent.

The above definitions oversimplify conditions that in clinical practice mostly present as complex phenomena. Indeed, most researchers endorse the view that depersonalisation constitutes a syndrome which, in addition to ineffable feelings of ‘unreality’, also includes emotional numbing, heightened self-observation, changes in body experience, distortions in the experiencing of time and space, changes in the feeling of agency, feelings of having the mind empty of thoughts, memories and/or images, and an inability to focus and sustain attention (Lewis, 1931, Mayer-Gross, 1935, Saperstein, 1949, Ackner, 1954). Elsewhere, we have proposed a model that renders the above clinical phenomena amenable to neurobiological research (see Sierra and Berrios, 1998). In short, we suggest that the clinical features of depersonalisation result from two simultaneous mechanisms: an inhibition of emotional processing, and a heightened state of alertness (i.e. akin to vigilant attention). Emotional numbing and lack of emotional colouring accompanying perceptual and cognitive processes would result from the inhibitory process, whereas the so-called feelings of ‘mind emptiness’, increased perceptual acuity, and feelings of lack of agency would result from the heightened alertness. This model is one of the sources (other sources are discussed below) of the scale herewith to be reported.