Psychotic experiences such as hearing voices have classically been viewed as representative of severe forms of mental illness. However, recent research has begun to suggest that low level psychotic phenomena may be more common than previously thought (van Os et al. 2008). These experiences are mainly transitory, resolving in between 75-90% of cases.

Psychotic symptoms are also common in mental disorders previously classified as non-psychotic, for example mood disorders (Kelleher et al. 2011).

The development of these symptoms is known to be associated with exposure to trauma; for example childhood bullying or abuse (Kelleher et al. 2013). The presence of dose-response relationships and cessation of psychotic phenomena on removal of trauma suggests a causative relationship.

What is unclear is the mechanism linking childhood experience and psychotic phenomena; not all children exposed to abuse will go onto develop psychotic symptoms for example.

To increase understanding in this area, recent research published in the British Journal of Psychiatry seeks to explore further the interplay of risk factors; adverse life events, childhood adversity and cannabis use with the development of low-level psychotic experiences (Morgan et al. 2014).

Methods

The authors made use of a cross-sectional study design to address their hypotheses:

1. Childhood adversity, life events and cannabis would be associated singly and cumulatively with psychotic experiences
2. Childhood abuse would combine synergistically with
   • Life events
   • Cannabis use

Participant interviews

• Participants were recruited from households within the target area (South East London) and involved all household residents aged 16 or older
• Computer-assisted face to face interviews were used to collect data
• The psychosis screening questionnaire (a standardised measure) was used to screen for psychotic experiences. It assessed:
  • Thought disorder
  • Paranoia
  • Strange experiences
  • Hallucinations
• Questions were asked relating to childhood experiences of physical and sexual abuse
• Sociodemographic and socioeconomic information were gathered
• Previous illicit substance and cannabis use was recorded
• Symptoms of common mental disorder were recorded, using a structured clinical interview schedule

Data analysis

Participants who reported a past diagnosis of psychotic disorder were excluded from the analysis.

To assess their hypotheses, the authors initially used a logistic regression approach to explore the relationship between childhood adversity, life events and cannabis use with psychotic experiences. Remaining data were used as possible confounding variables.

They also tested for an additive synergistic interaction between childhood abuse and life events or cannabis use; that is, do those exposed to both childhood abuse and cannabis use experience a greater risk of psychotic events than the sum of risks for those exposed to childhood abuse and cannabis use alone?

Results: the risk of psychotic experiences

• In total, after exclusion for missing data and previous psychotic disorder diagnosis, the authors had access to data for 1,680 participants (mean age 39, 44% men)
• 17.9% of participants described psychotic experiences in the past year
  • Paranoia was the most commonly endorsed experience (13.2%)
• Factors associated with increased psychotic experiences included:
  • Young age (16-29 years vs 30+ years)
  • Ethnicity (Other than White British)
  • Unemployment
  • Any common mental disorder (mixed anxiety/depression, depression or anxiety)
• University level education was associated with a decrease in risk for psychotic experience
• Cannabis use in the past year, but not prior, was associated with an increased risk for psychotic experience

Childhood abuse

• Psychotic experiences were associated with:
  • Physical abuse: Odds ratio (OR) 2.17 (95% confidence interval (CI) 1.62 to 2.89)
  • Sexual abuse: OR 2.13 (95% CI 1.28 to 3.56)
  • Physical and sexual abuse: OR 3.24 (95% CI 1.68 to 6.25)

Life events

• Nine life events were measured for and at least one was endorsed by 89% of participants, with 25% reporting at least one event in the past year
• Life events associated with an increased rate of psychotic experiences, if ever experienced:
  1. Separated from partner
  2. Loved one died
  3. No money for rent
  4. Been in serious accident
  5. Witnessed violence
  6. Victim of crime
  7. Attacked
  8. Injured with weapon
• Life events associated with increased risk of psychotic experiences, if exposure occurred in the past year:
  1. Separated from partner
  2. Loved one died
  3. Been in serious accident
  4. Attacked
• There was a linear association between the number of events experienced and the risk of psychotic experiences:
  • Each event ever experienced added an additional OR 1.45 (95% CI 1.32 to 1.59)
  • Each event experienced in the past year added an additional OR 1.7 (95% CI 1.44 to 2.00)

Synergistic interactions

• There was statistically significant evidence of an additive synergistic interaction between childhood abuse and experienced life events
• Cannabis use in the past year and past childhood abuse interacted with a suggestion of synergism, but this was not statistically significant

Conclusions

The authors conclude:

Our findings are consistent with the hypothesis that childhood abuse creates an enduring vulnerability to psychosis that is realised in the event of exposure to further stressors and risk factors.

Discussion

This paper adds additional evidence for the interaction between childhood abuse, adverse life events and psychotic experience. Being a cross-sectional design it cannot demonstrate causation and further study, as always, is required to explore the nature of these observations in further detail.

The study is also limited by its superficiality – for example the nature of the alleged psychotic phenomena has not been explored in detail and in relation to endorsed life events; the most commonly endorsed experience (paranoia) could be seen as appropriate after one has been injured with a weapon for instance? Similarly the amount of cannabis use and impact of psychotic phenomena on personal life remains unexplored here.

Despite these limitations this study serves as further support of the need for detailed consideration of life events during clinical assessment, as their presence, and likely the individual’s interpretation of this experience, are related to the experience of psychotic phenomena.

Links

Morgan C, Reininghaus U, Reichenberg A, Frissa S; SELCoH study team, Hotopf M, Hatch SL. Adversity, cannabis use and psychotic experiences: evidence of cumulative and synergistic effects. Br J Psychiatry. 2014 May;204:346-53. doi: 10.1192/bjp.bp.113.134452. Epub 2014 Mar 13.

van Os J, Linscott RJ, Myin-Germeys I, Delespaul P, Krabbendam L. A systematic review and meta-analysis of the psychosis continuum: evidence for a psychosis proneness-persistence-impairment model of psychotic disorder. Psychol Med. 2009 Feb;39(2):179-95. doi: 10.1017/S0033291708003814. Epub 2008 Jul 8. [PubMed abstract]

Kelleher I, Harley M, Murtagh A, Cannon M. Are screening instruments valid for psychotic-like experiences? A validation study of screening questions for psychotic-like experiences using in-depth clinical interview. Schizophr Bull. 2011 Mar;37(2):362-9. doi: 10.1093/schbul/sbp057. Epub 2009 Jun 19.

Kelleher I, Keeley H, Corcoran P, Ramsay H, Wasserman C, Carli V, Sarchiapone M, Hoven C, Wasserman D, Cannon M. Childhood trauma and psychosis in a prospective cohort study: cause, effect, and directionality. Am J Psychiatry. 2013 Jul 1;170(7):734-41. doi: 10.1176/appi.ajp.2012.12091169. [PubMed abstract]