Association between psychotic experiences and depression in a clinical sample over 6 months
Introduction
Psychotic-like experiences (PLEs) are present not only in clinically unwell individuals with psychotic disorders, but in the general population as well (Eaton et al., 1991, Scott et al., 2006, Tien, 1991, van Os et al., 2001). Some have hypothesised that these PLEs may be milder forms of clinical psychotic symptoms, that is they are quantitatively rather than qualitatively different (van Os et al., 2000, Yung et al., 2005). That is, they may differ, for example, in intensity, frequency, and/or associated distress level, rather than being phenomenologically distinct. There are several strands of evidence for this continuum theory. First, family members of schizophrenic probands show PLEs in higher levels than controls (Asarnow et al., 2001, Kety et al., 1994). Furthermore, family members with PLEs have been found to have neuropsychological deficits similar to schizophrenia patients, (Cadenhead et al., 1999, Cadenhead et al., 2000, Cadenhead et al., 2002, Chen et al., 1998, Clementz et al., 1998, Laurent et al., 2000, McDowell et al., 2001). Additionally, many of the risk factors for schizophrenia are the same as those for high levels of PLEs, including low level of education, low quality of life (van Os et al., 2000), low socio-economic status (Scott et al., 2006), exposure to influenza (Machon et al., 2002) and urbanicity (Scott et al., 2006, van Os et al., 2001). Finally, PLEs in community samples have been found to be associated with onset of psychotic disorders in longitudinal follow-up studies (Chapman et al., 1994, Poulton et al., 2000).
PLEs in ultra high risk (UHR) (ie putatively prodromal) populations are also associated with onset of psychotic disorders in longitudinal follow-up studies (Haroun et al., 2006, Mason et al., 2004, Miller et al., 2002, Yung et al., 2003, Yung et al., 2004). These UHR samples differ from community samples in that individuals are help-seeking and usually distressed, in addition to having PLEs. Their psychosocial functioning is generally low and they often have other psychiatric syndromes in addition to PLEs such as major depression or anxiety disorders (Rosen et al., 2006, Svirskis et al., 2005).
PLEs have also been found in non-psychotic patient populations (Olfson et al., 2002, Verdoux et al., 1998, Verdoux et al., 1999, Yung et al., 2006a, Yung et al., 2006b). The relationship between these samples and UHR groups is not distinct and is becoming increasingly blurred as detection of UHR individuals expands into general psychiatric services and primary care (Yung et al., 2006b). The degree of risk PLEs represent in non-psychotic populations needs further examination. In over 10 years of clinical experience with UHR patients we find that PLEs can wax and wane against a background of non-psychotic symptoms or disorder. This further blurs the division between UHR groups and non-psychotic patient populations.
Given the above considerations, we have previously proposed that a continuity exists between community PLEs, PLEs in non-psychotic populations, UHR groups and threshold psychotic disorder (Yung et al., 2006b). Clearly, not all people with PLEs in the community will go on to develop psychiatric syndromes, and not all people with PLEs and non-psychotic disorders will progress to UHR status or frank psychotic disorder. Mediating factors such as distress and depression may influence the outcome (Johnstone et al., 2000, Johnstone et al., 2005, Owens et al., 2005, Yung et al., 2003).
Within this theoretical background, this study set out to examine the influence of depression on PLEs present in a clinical sample of non-psychotic young people aged 15–24. We previously studied a population of young people presenting to a mental health service with non-psychotic disorders (Yung et al., 2006a). We found that PLEs were common in this group: 78.6% of participants endorsed at least one positive psychotic symptom at least ‘often’ in a self-report measure, the Community Assessment of Psychic Experiences (CAPE). PLEs consisted of three types: Bizarre Experiences (BE; e.g. ‘Do you ever hear voices when you are alone?’), Persecutory Ideation (PI; e.g. ‘Do you ever feel as if there is a conspiracy against you?’) and Magical Thinking (MT; e.g. ‘Do you think people can communicate telepathically?’) (Yung et al., 2006a). BE and PI were found to be significantly correlated with poor functioning and depression, but MT was not. Thus we hypothesised that BE and PI may be maladaptive and possibly associated with high risk of transition to full blown psychotic disorder, but that MT may be benign and not associated with the same degree of risk. However one issue which needed further exploration was the association of PLEs with depression. There was a high prevalence of depressive disorders and symptoms. However, because this was a cross sectional study, we were unable to draw conclusions about the association between PLEs and depression. People with PLEs may have become depressed as a result of their unusual and sometimes frightening experiences, or the depression may have resulted in PLEs, for example exaggerated self-consciousness and low self-esteem leading to persecutory fears. There is evidence that PLEs may be an intrinsic part of a depressive syndrome (Verdoux et al., 1998, Verdoux et al., 1999). Alternatively, an emerging psychotic disorder may be initially manifested by depressive symptoms and low level PLEs (Krabbendam et al., 2005, Moller and Husby, 2000, Owens et al., 2005, Yung and McGorry, 1996). Depression is a common prodromal symptom in schizophrenia and other psychotic disorders (Hafner et al., 2005), and may increase the likelihood of transition to full blown psychotic disorder in individuals at high risk (Yung et al., 2004). Thus the relationship between PLEs and depression is important to explore. In order to further investigate this we undertook a longitudinal study of the previous cohort (Yung et al., 2006a). We wished to discover if PLEs persisted even if depression level reduced. It was hypothesised that when participants experienced an improvement in their depression, that levels of PLEs would likewise reduce.
Section snippets
Setting
ORYGEN Youth Health (OYH) is a public mental health program for young people aged between 15 and 24 years living in metropolitan Melbourne, Australia. The clinical service has three components, EPPIC (the Early Psychosis Prevention and Intervention Centre, a service for people with first episode psychotic disorder), PACE, a service for those thought to be at ultra high risk (UHR) of imminent psychotic disorder (i.e. “prodromal”), and Youthscope (a service for non-psychotic individuals).
Characteristics of the sample
Of the 149 participants who completed the baseline assessment, 105 completed the CAPE and the MASQ: AD at follow-up (75.0% of original sample) and 98 (70% of the original sample) completed all three assessments at 6 month follow-up (diagnostic interview, CAPE and MASQ: AD). There was no significant difference in the proportion of depressed people at baseline who did (62.5%) versus did not (37.5%) participate in the follow-up. There were no significant differences in baseline CAPE and MASQ:AD
Discussion
In recent years there has been a growth in the study of individuals hypothesised to be at Ultra High Risk (UHR) or in the prodromal phase of psychotic disorders (Killackey and Yung, in press). UHR or prodromal individuals are generally identified by virtue of having PLEs in conjunction with help-seeking (Miller et al., 2002, Yung et al., 2003). People presenting to generalist services with PLEs are not distinct from those presenting to UHR or “prodromal” services and the boundary between them
Acknowledgements
This study was funded by a generous donation from the Colonial Foundation philanthropic trust. The authors thank Gennady Baksheev, Adrienne Brown, Katherine Godfrey and Carrie Stanford for their assistance with data collection.
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