Severity of thought disorder predicts psychosis in persons at clinical high-risk
Introduction
Development of preventative interventions for schizophrenia requires identifying persons at very high risk. An early study examining psychosis conversion in persons meeting high-risk diagnostic criteria reported a 45% 2-year conversion rate (Yung et al., 2004), however subsequent studies found 2-year conversion rates that ranged from 15 to 30% (Demjaha et al., 2012, DeVylder et al., 2014, Katsura et al., 2014, Lee et al., 2014, Liu et al., 2011, Nelson et al., 2013, Riecher-Rossler et al., 2009, Ruhrmann et al., 2010, Woods et al., 2009, Ziermans et al., 2011). Efforts are needed to improve psychosis risk prediction.
Prominent among the scales used to evaluate symptoms associated with psychosis risk is the Scale of Psychosis-Risk Symptoms (SOPS) (McGlashan et al., 2010, Miller et al., 2002). The SOPS comprises 19 symptoms in four domains that include: positive (unusual thought content/delusional ideas, suspiciousness/persecutory ideas, grandiose ideas, perceptual abnormalities/hallucinations, disorganized communication), negative (social anhedonia, avolition, decreased expression of emotion, decreased experience of emotions and self, reduced ideational richness, reduced occupational functioning), disorganized (odd behavior or appearance, bizarre thinking, trouble with focus and attention, impaired hygiene), and general (sleep disturbance, dysphoric mood, motor disturbances, impaired stress tolerance). The symptoms evaluated by the SOPS were chosen to reflect broadly the symptoms experienced by persons with schizophrenia during their prodrome.
We sought to identify among items measured by the SOPS subsets that best predicted psychosis conversion. We considered two large independent cohorts, the North American Prodrome Longitudinal Study Cohort-1 and the North American Prodrome Longitudinal Study Cohort-2. This allowed construction of risk prediction subscales in Cohort-1 and evaluation of subscale performance in Cohort-2.
Section snippets
Subjects
Detailed study methods were reported previously (Addington et al., 2007, Addington et al., 2012, Cannon et al., 2008). In brief, the North American Prodrome Longitudinal Study is a multisite observational study of the predictors and mechanisms of conversion to psychosis in persons meeting Criteria of Psychosis-Risk Syndromes (COPS) (Miller et al., 2003). There were two non-overlapping waves of recruitment, Cohort-1 and Cohort-2. For Cohort-1 a database combined the results post hoc from eight
Study subjects (Table 1)
Baseline evaluations for Cohort-1 occurred in 1998–2005 and for Cohort-2 in 2008–2013. Compared to included subjects, excluded subjects had significantly lower parental education in both cohorts. For Cohort-1, the diagnosis at conversion was known for 59 (66%): Bipolar Disorder (n = 6), Brief Psychotic Disorder (n = 2), Delusional Disorder (n = 2), Psychosis NOS (n = 16), Schizoaffective Disorder (n = 6), Schizophrenia (n = 15), and Schizophreniform Disorder (n = 12). For Cohort-2, the diagnosis at
Discussion
The performance of the 2-Item subscale indicates that the severity of unusual thought content (P1), referential thinking (both P1,P2) and suspiciousness (P2) are key high-risk symptoms. The majority of published studies examining symptoms and risk prediction likewise have reported that items reflecting disordered thought content (unusual ideas (Katsura et al., 2014, Nelson et al., 2013, Salokangas et al., 2013, Thompson et al., 2013, Thompson et al., 2011, Wilcox et al., 2014), suspiciousness (
Role of the funding source
This project was a cooperative agreement between the investigator sites and the National Institutes of Health.
Contributors
Drs. Perkins and Jeffries contributed equally to the work. Drs. Perkins and Jeffries undertook the statistical analysis, and Dr. Perkins wrote the first draft of the manuscript. All of the authors were involved in study design, contributed to and have approved the final manuscript.
Conflict of interest
The authors declare that they have no actual or potential conflict of interest including any financial, personal or other relationships with other people or organizations within three (3) years of beginning the work submitted that could inappropriately influence, or be perceived to influence, their work.
Acknowledgments
U01 MH081902 (Cannon), P50 MH066286 (Bearden), U01 MH081857 (Cornblatt), U01 MH82022 (Woods), U01 MH066134 (Addington), U01 MH081944 (Cadenhead), R01, U01 MH066069 (Perkins, Jeffries), MH076989 (Mathalon), U01 MH081928 (Seidman), and U01 MH081988 (Walker).
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