The Cambridge Depersonalisation Scale: a new instrument for the measurement of depersonalisation
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.
Section snippets
Dixon’s scale
A self-administered questionnaire, Dixon’s scale (Dixon, 1963) addresses depersonalisation as a symptom and includes 12 items selected out of a larger pool by means of factor analysis. Piloted in a sample of normal college students, to our knowledge it has only been used in a couple of studies (Melges et al., 1970, Mathew et al., 1993). Trueman (1984) has questioned its validity.
There are two main problems with Dixon’s scale. Firstly, it includes clinical features not considered as part of the
Subjects
The scale was tried on a sample of 77 subjects: 35 patients meeting DSM-IV criteria for depersonalisation disorder, 22 with DSM-IV panic disorder or generalised anxiety disorder, and 20 with temporal lobe epilepsy (TLE). The mean age of the sample was 34 years (S.D. 10.2; range 18–60), and 50% were females. Patients were examined consecutively in a ‘Depersonalisation and Anxiety Disorders Clinic’ (GEB) and a ‘Seizure Disorder Clinic’ (GEB) (Addenbrooke’s Hospital, Cambridge University).
Development: item source and piloting
A
Results
Cronbach alpha and split-half reliability were 0.89 and 0.92, respectively, and correlations between item scores and corrected global scores ranged from 0.3 to 0.86. Lower correlations were obtained for items which, although not part of the depersonalisation syndrome, can accompany it occasionally: déjà vu (0.41); autoscopy (0.41); micropsias (0.56); feelings of hand or feet enlargement (0.47); and not experiencing hunger or other bodily needs (0.33). Correlations for all the core items of
Discussion
The scale reported in this article has been found to be a reliable and valid instrument to measure depersonalisation disorder. Global scores were able to differentiate patients with depersonalisation disorder from patients with anxiety disorders and patients with TLE. We take the latter as reflecting high validity of our instrument, since it is well known that patients with anxiety or TLE frequently suffer from depersonalisation experiences (in fact, 50 and 80% of our samples, respectively,
Summary and conclusions
Despite the fact that one century has elapsed since the naming and conceptualisation of depersonalisation (Sierra and Berrios, 1996), little systematic research has been carried out in relation to its phenomenology and neurobiology. One stumbling block has been the absence of valid and reliable scales. Available scales are not comprehensive from the phenomenological point of view, and this is a serious shortcoming for we do not know yet which clinical features of depersonalisation are relevant
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