Psychosis-like experiences (PEs) are common in patients with non-psychotic disorders. Several factors predict reporting of PEs in mood disorders, including mood-associated cognitive biases, anxiety and features of borderline personality disorder (BPD). Childhood traumatic experiences (CEs), often reported by patients with BPD, are an important risk factor for mental disorders. We hypothesized that features of BPD may mediate the relationship between CEs and PEs. In this study, we investigated the relationships between self-reported PEs, CEs and features of BPD in patients with mood disorders.

As part of the Helsinki University Psychiatric Consortium study, McLean Screening Instrument (MSI), Community Assessment of Psychic Experiences (CAPE-42) and Trauma and Distress Scale (TADS) were filled in by patients with mood disorders (n = 282) in psychiatric care. Correlation coefficients between total scores of scales and their dimensions were estimated, multiple regression and mediation analyses were conducted.

Total scores of MSI correlated strongly with scores of the CAPE-42 dimension “frequency of positive symptoms” (rho = 0.56; p ≤ 0.001) and moderately with scores of TADS (rho = 0.4; p ≤ 0.001). Total score of MSI and its dimension “cognitive symptoms”, including identity disturbance, distrustfulness and dissociative symptoms, fully mediated the relation between TADS and CAPE-42. Each cognitive symptom showed a partial mediating role (dissociative symptoms 43% (CI = 25–74%); identity disturbance 40% (CI = 30-73%); distrustfulness 18% (CI = 12-50%)).

Self-reported cognitive-perceptual symptoms of BPD fully mediate, while affective, behavioural and interpersonal symptoms only partially mediate the relationships between CEs and PEs. Recognition of co-morbid features of BPD in patients with mood disorders reporting PEs is essential.