Anomalous self-experience in substance-induced and primary psychotic disorders: a cross-sectional comparative study using the EASE interview.

Abstract

Background: Disturbances of the minimal self, or anomalous self-experiences (ASEs), are increasingly regarded as a core feature of primary psychotic disorders (PPDs). However, it remains unclear whether similar self-disorders are present in substance-induced psychosis (SIP), a condition that often mimics PPDs in its early stages.

Objective: The study aims to compare ASEs between PPD and SIP using the EASE interview, to evaluate the diagnostic specificity of ASEs and determine whether these disturbances are exclusive to primary psychoses or also present in SIP.

Methods: A total of 54 clinically stable patients were recruited from psychiatric centers in Italy (27 with schizophrenia spectrum disorders (SSD), mean age ≈ 27 years; 27 with substance-induced psychosis, mean age ≈ 28 years).. Diagnoses were established according to DSM-5 criteria. ASEs were assessed using the Examination of Anomalous Self-Experience (EASE) interview, and scores were compared across five experiential domains. Non-parametric statistics and logistic regression were employed to identify domain-specific differences and their diagnostic utility.

Results: While total EASE scores did not differ significantly between groups, Domain 4 (Demarcation/Transitivism) was significantly higher in the SIP group (p < .0001, r = .72), contrary to classical phenomenological models that typically associate self-world boundary disturbances with schizophrenia spectrum disorders. In contrast, Domain 2 (Self-awareness and Presence) trended higher in the PPD group (p = .049, r = .27) and Domain 5 (Existential Reorientation) showed a similar trend (p = .098, r = .22)., aligning with classical phenomenological models of schizophrenia. Logistic regression confirmed the predictive value of these domains for group classification.

Conclusion: ASEs are not exclusive to PPDs and may also manifest in SIP, particularly in the domain of "self-world boundary" disturbances. These findings challenge the assumption that self-disorders are unique to endogenous psychosis and highlight the need for refined phenomenological assessment in early diagnostic work. Longitudinal studies are needed to clarify whether ASEs in SIP represent transient phenomena or prodromal markers of schizophrenia.