Delusional Themes are More Varied Than Previously Assumed: A Comprehensive Systematic Review and Meta-Analysis

Delusions are classified into themes but the range of themes reported in the literature has never been examined and the extent to which they differ in prevalence, or relate to clinical characteristics or cultural variation, remains poorly understood.

We identified studies reporting delusional theme prevalence in adults with psychosis and completed two multivariate, multilevel, random-effects meta-analyses: one including data from structured assessment scales only and another also including data from ad hoc and clinical assessments to include themes from a wider range of countries and contexts. Sensitivity and meta-regression analyses examined the association with clinical and methodological variables. Analysis code and open data are available online. PROSPERO registration (CRD42019151889).

A total of 155 studies from 37 countries met inclusion criteria. The meta-analysis of data from structured assessments included 110 studies and 173 920 patients. A total of 21 themes were identified from "persecutory/paranoid" (57.33%, 53.75-60.88) to "primary" (5.18%, 1.07-11.55). The meta-analysis of all data included 155 studies and 240 901 patients. Thirty-seven themes were identified, from "persecutory/paranoid" (57.39%, 54.38-60.37) to "made impulse" (4.90%, 0.87-11.26). Ad hoc theme classifications were more common in non-Western contexts. Including these did not substantially alter heterogeneity but increased interaction with cultural clusters. There was no evidence of publication bias or association with risk of bias rating.

We report the first comprehensive meta-analysis of delusional themes. Many commonly reported themes are not included in standard classifications. Relationship to culture was modest but more present when not relying solely on established scales.