Improvement of personality functioning in patients with personality disorders: a comparative study of mentalization-based treatment versus non-manualized treatments

Objective Among evidence-based treatments for personality disorder (PD), mentalization-based treatment (MBT) represents a manualized, long-term treatment. Both MBT and non-manualized psychotherapeutic treatments (NMT) are currently applied for patients with PDs in Norway. This clinical population is characterized by varying impairment of personality functioning (PF). Few have investigated how MBT and NMT are suited for the heterogeneity of personality problems presenting to health services and how they compare. This study aimed to investigate 1) characteristics of patients admitted to MBT versus NMT, 2) longitudinal change in PF among patients in MBT versus NMT, and 3) associations between initial PD status and outcome differences in MBT and NMT. Methods The current study is observational, reflecting regular outpatient PD health services. Data was retrieved from a Norwegian quality registry (Network for Personality Disorders, period 2017-2024) and included all patients with information on baseline PD assessment (SCID-5-PD), treatment specification (i.e., MBT or NMT), and self-report data on PF outcome (global level of personality functioning: LPFS-BF, and specific personality problems: SIPP-SF, N = 954, N MBT = 565, N NMT = 389). Longitudinal estimations were based on linear mixed models. Results Patients admitted to MBT treatment had more severe personality pathology, more often a Borderline PD (BPD) diagnosis, and a higher symptom burden compared to NMT. Treatment condition explained little longitudinal variation and improvement of all PF aspects during treatment was comparable. Effect sizes ranged from medium to large in both treatment groups. Increasing number of borderline and narcissistic PD criteria were independently associated with greater improvement in MBT versus NMT. Poorer improvement in MBT was associated with a higher number of avoidant PD (AvPD) criteria. Conclusion Admittance to MBT versus NMT appeared largely matched to severity and type of PD. Clinically relevant improvements were found in both MBT and NMT. Improvement rates were larger in MBT for patients with BPD, more severe PD conditions, and comorbid narcissistic traits. Further development of effective treatments for AvPD is needed.