Examining the Discriminant Validity of Complex Posttraumatic Stress Disorder and Borderline Personality Disorder Symptoms: Results From a United Kingdom Population Sample

Complex Posttraumatic Stress Disorder (CPTSD) was added to the diagnostic nomenclature in the 11th version of the International Classification of Diseases (ICD-11). Although considerable evidence exists supporting the construct validity of CPTSD, the distinguishability of CPTSD symptoms from those of Borderline Personality Disorder (BPD) has been questioned. This study examined the discriminant validity of CPTSD and BPD symptoms among a trauma-exposed population sample from the United Kingdom (N = 546). Participants completed self-report measures of CPTSD and BPD symptoms, and their latent structure was assessed using exploratory structural equation modelling (ESEM). A three-factor model with latent variables reflecting ‘PTSD, ‘Disturbance in Self-Organization’ (DSO), and ‘BPD’ symptoms provided the best fit of the data (χ2 (399) = 1650, p < .001; CFI = .944; TLI = .930; RMSEA = .077 [90% CI = .073 - .081]). Multiple symptoms were identified distinguishing each construct (e.g., disturbed relationships and suicidality), as well as symptoms shared across the constructs (e.g., affective dysregulation). The PTSD (β = .24), DSO (β = .23), and BPD (β = .27) latent variables were positively and significantly associated with childhood interpersonal trauma. The current findings support the discriminant validity of CPTSD and BPD symptoms, highlight some of the phenomenological signatures of each construct, but also show how these constructs share important similarities in symptom composition and exogenous correlates