Longitudinal Changes in Maladaptive Personality Domains and Clinical Outcomes: A Study Protocol

Background: Maladaptive personality traits are transdiagnostic risk factors associated with functional impairment, lower treatment efficacy, and poor mental health outcomes. These traits, encompassing domains such as Negative Affectivity, Detachment, Antagonism, Disinhibition, Psychoticism, and Anankastia, contribute to difficulties in emotional regulation, interpersonal relationships, and occupational functioning. While increasing evidence suggests that personality traits can change over time, longitudinal research examining within-person fluctuations in maladaptive traits during psychotherapy remains limited. Methods: This preregistered longitudinal study investigates the dynamic interplay between maladaptive personality domains and treatment outcomes in patients undergoing Cognitive Behavioral Therapy (CBT). A total of 200 participants will be recruited from an Italian outpatient psychotherapy service and assessed across five time points over one year (baseline, 3, 6, 9, and 12 months). At each point, participants will complete validated self-report measures of personality domains and clinical symptoms (anxiety, depression, psychosocial functioning). The study will use Random Intercept Cross-Lagged Panel Models to examine reciprocal relationships between personality traits and clinical outcomes while distinguishing between within-person fluctuations and between-person differences. Latent Growth Curve Models will be used to assess mean-level change in personality traits over time. An exploratory analysis will examine whether patients show the greatest change in the trait domain most elevated at baseline. Discussion: This study will provide novel insights into the temporal dynamics of maladaptive personality traits during CBT and their association with therapeutic change. Identifying which traits change most significantly - and whether these changes predict symptom improvement - may inform the development of more personalized interventions. The findings may also guide clinical decision-making by highlighting which personality factors influence treatment trajectories, ultimately supporting better planning and outcomes for patients with elevated maladaptive traits.