Cannon M. Prevalence of psychotic symptoms in childhood and adolescence: a systematic review and meta-analysis of population-based studies. Psychological Medicine. 2012; 9:1-7. AuthorsIan Kelleher, Dearbhla Connor, Mary C. Clarke, Nina Devlin, Michelle Harley, and Mary Cannon This article is available at e-publications@RCSI: http://epubs.rcsi.ie/psychart/1 -Use LicenceAttribution-Non-Commercial-ShareAlike 1.0 You are free:• to copy, distribute, display, and perform the work.• to make derivative works. Under the following conditions:• Attribution -You must give the original author credit.• Non-Commercial -You may not use this work for commercial purposes.• Share Alike -If you alter, transform, or build upon this work, you may distribute the resulting work only under a licence identical to this one.

Hallucinations and delusions, the classic symptoms of psychosis, have recently been documented to occur at a much higher prevalence in the general population than clinically diagnosed psychotic disorder.1 A meta-analysis of prevalence studies of psychotic symptoms in young people demonstrated a median prevalence of 17% in children aged 9-12 years and 7.5% in adolescents aged 13-18 years.2 As the term suggests, psychotic symptoms have typically been considered to relate to psychotic disorder. Indeed, research has shown that members of the general population who report psychotic symptoms share a wide range of risk factors with people with schizophrenia (see Kelleher & Cannon for review), [3][4][5][6][7][8][9] and young people who report psychotic symptoms have been found to be at increased risk of psychotic disorder in adulthood.10,11 Individuals who report psychotic symptoms are also more likely to report non-psychotic psychopathological symptoms, especially symptoms of depression; [12][13][14][15][16] Yung et al, for example, reported that individuals who had a diagnosed depressive disorder endorsed an increased number of psychotic symptoms on the Community Assessment of Psychic Experiences questionnaire compared with controls.17 Bartels-Velthuis et al found that young adolescents who disclosed psychotic symptoms were approximately 3-5 times more likely to score in the clinical psychopathology range on the parent-completed Child Behavior Checklist. Community-based studies to date, however, have relied mainly upon questionnaires to assess psychotic symptoms and have involved limited data on non-psychotic psychopathology. In addition, although research suggests that psychotic symptoms are more common in younger than in older children, 2 there is a lack of information on whether there are differences in the clinical significance of psychotic symptoms across different stages of adolescence. In an attempt to improve our understanding of the clinical significance of psychotic symptoms in the general population we examined data from four population studies, comprising two large population surveys and two in-depth clinical interview studies of psychotic symptoms. The aims of this work were to investigate whether psychotic symptoms predicted nonpsychotic clinical diagnoses, and if so, which disorders; to investigate whether psychotic symptoms predicted more clinically severe disorder in terms of comorbid psychopathology (i.e. having more than one diagnosis); and to investigate whether the significance of psychotic symptoms varied as a function of age. MethodSurvey studies Background Epidemiological research has shown that hallucinations and delusions, the classic symptoms of psychosis, are far more prevalent in the population than actual psychotic disorder. These symptoms are especially prevalent in childhood and adolescence. Longitudinal research has demonstrated that psychotic symptoms in adolescence increase the risk of psychotic disorder in adulthood. There has been a lack of research, however, on the immediate clini...

Individuals who report psychotic-like experiences are at increased risk of future clinical psychotic disorder. They constitute a unique "high-risk" group for studying the developmental trajectory to schizophrenia and related illnesses. Previous research has used screening instruments to identify this high-risk group, but the validity of these instruments has not yet been established. We administered a screening questionnaire with 7 items designed to assess psychotic-like experiences to 334 adolescents aged 11-13 years. Detailed clinical interviews were subsequently carried out with a sample of these adolescents. We calculated sensitivity and specificity and positive predictive value (PPV) and negative predictive value (NPV) for each screening question for the specific symptom it enquired about and also in relation to any psychotic-like experience. The predictive power varied substantially between items, with the question on auditory hallucinations ("Have you ever heard voices or sounds that no one else can hear?") providing the best predictive power. For interview-verified auditory hallucinations specifically, this question had a PPV of 71.4% and an NPV of 90.4%. When assessed for its predictive power for any psychotic-like experience (including, but not limited to, auditory hallucinations), it provided a PPV of 100% and an NPV of 88.4%. Two further questions-relating to visual hallucinations and paranoid thoughts-also demonstrated good predictive power for psychotic-like experiences. Our results suggest that it may be possible to screen the general adolescent population for psychotic-like experiences with a high degree of accuracy using a short self-report questionnaire.

While a great deal of research has been conducted on prodromal risk syndromes in relation to help-seeking individuals who present to the clinic, there is a lack of research on prodromal risk syndromes in the general population. The current study aimed first to establish whether prodromal risk syndromes could be detected in non-help-seeking community-based adolescents and secondly to characterize this group in terms of Axis-1 psychopathology and general functioning. We conducted in-depth clinical interviews with a population sample of 212 school-going adolescents in order to assess for prodromal risk syndromes, Axis-1 psychopathology, and global (social/occupational) functioning. Between 0.9% and 8% of the community sample met criteria for a risk syndrome, depending on varying disability criteria. The risk syndrome group had a higher prevalence of co-occurring nonpsychotic Axis-1 psychiatric disorders (OR 5 4.77, 95% CI 5 1.81-12.52; P < .01) and poorer global functioning (F 5 24.5, df 5 1, P < .0001) compared with controls. Individuals in the community who fulfill criteria for prodromal risk syndromes demonstrate strong similarities with clinically presenting risk syndrome patients not just in terms of psychotic symptom criteria but also in terms of co-occurring psychopathology and global functioning.

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BackgroundAdolescent cannabis use has been shown in many studies to increase the risk of later psychosis. Childhood trauma is associated with both substance misuse and risk for psychosis. In this study our aim was to investigate whether there is a significant interaction between cannabis use and childhood trauma in increasing the risk for experiencing psychotic symptoms during adolescence.MethodPsychiatric interviews using the Schedule for Affective Disorders and Schizophrenia for School-Age Children (K-SADS) semi-structured instrument were carried out with 211 adolescents aged between 12 and 15 years and their parents as part of a population-based study. The interview enquired about early traumatic events, cannabis use and psychiatric symptoms in adolescence.ResultsIn separate analyses both cannabis use and childhood trauma were significantly associated with risk of experiencing psychotic symptoms. However, the presence of both childhood trauma and early cannabis use significantly increased the risk for psychotic symptoms beyond the risk posed by either risk factor alone, indicating that there was a greater than additive interaction between childhood trauma and cannabis use.ConclusionOur finding of a greater than additive interaction between childhood trauma and cannabis use may have implications for the identification of individuals at high risk of experiencing psychotic symptoms. For example, measures to actively discourage or intensively treat cannabis use in children and adolescents who have experienced abuse may help to prevent the development of psychosis in this vulnerable group. Our findings require replication in larger samples to confirm this interaction effect.

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