Childhood adversity and conduct disorder: A developmental pathway to violence in schizophrenia
Introduction
There is good epidemiological evidence to support a modest but significant association between schizophrenia and violence (Arseneault et al., 2000, Douglas et al., 2009, Large and Nielssen, 2011, Walsh et al., 2002) but the origins of this relationship remain unclear. Some argue that little violence risk is attributable to the mental illness itself, with the effects of substance abuse (particularly alcohol) and personality disorders outweighing the role of schizophrenia (Appelbaum, 2008).
It is established that co-morbid substance misuse increases the risk of violence in schizophrenia (Elbogen and Johnson, 2009, Fazel et al., 2009, Swanson et al., 2006). Controversy remains about the true extent of that role. Some studies have cited substance misuse as one of several factors that increase the risk of violent behaviour in patients with psychotic illnesses (Daffern et al., 2005, Dean et al., 2007, Harris et al., 2010, Stompe et al., 2004). Other large epidemiological studies have suggested that there is almost no role for psychosis-specific factors and that substance misuse is the main driver of violence in schizophrenia (Elbogen and Johnson, 2009, Fazel et al., 2009). However a reanalysis of the data from one of these (Elbogen and Johnson, 2009) found that those patients with severe mental illness, irrespective of substance abuse comorbidity, were significantly more likely to be violent than those with no mental illness (Van Dorn et al., 2012). Equally there is data that patients with schizophrenia without comorbid substance misuse, do have an elevated risk of violence (Short et al., 2013).
Antisocial personality disorder increases the risk for violence in men with schizophrenia (Volavka, 2014). In some patients with schizophrenia, personality pathology, including psychopathy, predicts violence regardless of schizophrenia symptoms (Bo et al., 2011). Taken together these findings have led to the suggestion that violence among patients with schizophrenia may follow at least two distinct pathways, one associated with premorbid conditions, including antisocial behaviour, and another linked with the acute psychotic symptoms of schizophrenia (Bo et al., 2011, Hodgins et al., 2014, Volavka, 2014, Volavka and Citrome, 2011).
Threat/control-override symptoms, principally delusions of persecution and passivity were advanced as a cognitive model for violence in psychosis (Link and Stueve, 1994). Though supporting evidence has remained limited (Appelbaum et al., 2000, Stompe et al., 2004). Other studies have concluded that positive psychotic symptoms do increase the risk of violence (Daffern et al., 2005, Hodgins et al., 2003, Krakowski et al., 1999, Swanson et al., 2006). Crucially there are early indicators that psychotic symptoms may be of particular relevance in relation to violence committed by patients with schizophrenia in the absence of preceding conduct disorder (Heads et al., 1997, Swanson et al., 2008).
Childhood physical abuse has been shown to be associated with later violent behaviour in general population (Elbogen and Johnson, 2009), patient (Hoptman et al., 1999, Witt et al., 2013) and prisoner (Sarchiapone et al., 2009) samples. However, less is known about the influence of other forms of childhood trauma on the risk of violence in people with schizophrenia.
Childhood adversity is strongly associated with an increased risk for psychosis and could have a significant aetiological role (Varese et al., 2012). For example, a prospective study in adolescents showed that childhood trauma was strongly predictive of new psychotic experiences and that stopping the trauma stopped the psychotic experiences (Kelleher et al., 2013). There is also evidence that childhood abuse and number of later life events combine synergistically to increase the odds of psychotic experiences beyond the effects of each risk factor alone (Morgan et al., 2014). However, other forms of childhood adversity, such as parental loss or separation also contribute to later psychopathology (Morgan et al., 2007). Hence there is a wider focus on the effects of childhood adversities in psychosis, rather than exclusively childhood trauma (Varese et al., 2012).
One important influence on the later effects of childhood adversity may be conduct disorder. Childhood abuse is associated with a wide range of later psychopathology (McCrory et al., 2012). Childhood adversity, including neglect and physical and sexual abuse, increases the risk of conduct disorder (Afifi et al., 2011, Foley et al., 2004, Maniglio, 2015, Villodas et al., 2014); while conduct disorder (CD) is over-represented in patients who later develop schizophrenia (Hodgins et al., 2008). Finally childhood CD is associated with an increased risk of violent behaviour in both the adult general population (Blair et al., 2014) and in those with schizophrenia (Arseneault et al., 2000, Hodgins et al., 2008, Swanson et al., 2008, Tengström et al., 2004).
In summary, there is emerging evidence that childhood adversity is associated with psychosis, CD and the risk of violence. However, it remains unclear how childhood adversity might interact with CD to contribute towards the increased risk of violence in schizophrenia. This study, therefore, sought to examine the association between childhood adversity and violence among men with schizophrenia and whether this varied on the basis of prior CD. Patients with schizophrenia are more likely to have been exposed to a variety of adverse childhood events including physical and sexual abuse; parental divorce, parental death; domestic violence; and foster care (Bennouna-Greene et al., 2011, Gibbon et al., 2009, Rosenberg et al., 2007). Therefore this study considered three types of childhood adversity: childhood abuse (physical or sexual); separation from either parent (due to reasons such as divorce, death, or being taken into foster care); and exposure to domestic violence. We hypothesised that among men with schizophrenia, those with prior CD would be more likely to (i) report childhood adversities and (ii) have a significantly greater history of violence, as compared to those without CD. We further hypothesised that childhood adversities would be associated with violence and that CD would be a mediator of the relationship between childhood adversities and violence.
Section snippets
Recruitment
After NHS Research Ethics Committee approval, male patients of working age with schizophrenia were recruited from four large National Health Service Mental Health Trusts and one independent sector provider. The sites had a range of mental health services for men with schizophrenia, including outpatient clinics and inpatient wards in acute as well as secure units. This approach offered representative sampling of male patients with schizophrenia in their respective catchment areas, across a wide
Sample characteristics
A total of 54 men with schizophrenia aged between 21 and 57 (mean 36) years old were recruited from the spectrum of mental health services. Thirty-four were white British, 6 white and black Caribbean, 6 black Caribbean, 5 Asian and 3 were of other ethnic backgrounds. The characteristics of the sample are shown in Table 1. Inter-rater reliability for the GRVS scores was 89.4%.
Univariate associations with violence
Age, ethnicity and current psychotic symptoms were considered as potential confounders based on the existing literature.
Discussion
In this study of men with schizophrenia, 94% of the most violent patients had experienced at least one form of childhood adversity. Exposure to domestic violence during childhood was associated with an increased propensity to violence in adulthood. The cumulative number of childhood adversities was associated with adult propensity to violence and attenuation of this association suggested that CD may be a mediator of the relationship.
Conclusions
Exposure to domestic violence during childhood was associated with violent behaviour in adulthood among men with schizophrenia. As far as we are aware, this is the first time this finding has been demonstrated. The association between cumulative childhood adversities and propensity to violence may be mediated by CD. This study emphasises the importance of developmental pathways to violence among men with schizophrenia. Further work is needed to advance our understanding of the complex interplay
Role of funding source
The study was funded by St Andrew's Healthcare (883). We also thank the National Institute for Health Research Biomedical Research Centre for Mental Health at South London and Maudsley NHS Foundation Trust and King's College London for their financial support.
Contributors
All authors were involved in the study design. CO and SH recruited and assessed the participants. CO conducted these statistical analyses and wrote the first draft of this manuscript. All authors contributed to and have approved this manuscript.
Conflict of interest
No authors have a conflict of interest to declare.
Acknowledgements
The authors are grateful to their local collaborators for assisting with identifying participants: Professor Femi Oyebode (Birmingham and Solihull Mental Health NHS Foundation Trust), Dr Steffan Davies (Northamptonshire Healthcare NHS Foundation Trust), Dr Evangelos Vassos (Oxford Health NHS Foundation Trust), and Dr Daniel Kinnair (Leicestershire Partnership NHS Trust). They would also like to thank Professor Philip Sugarman for his support of this research.
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