RESUMEN
BACKGROUND: Cluster-C personality disorders (PDs) are highly prevalent in clinical practice and are associated with unfavourable outcome and chronicity of all common mental health disorders (e.g. depression and anxiety disorders). Although several forms of individual psychotherapy are commonly offered in clinical practice for this population, evidence for differential effectiveness of different forms of psychotherapy is lacking. Also, very little is known about the underlying working mechanisms of these psychotherapies. Finding evidence on the differential (cost)-effectiveness for this group of patients and the working mechanisms of change is important to improve the quality of care for this vulnerable group of patients. OBJECTIVE: In this study, we will compare the differential (cost)-effectiveness of three individual psychotherapies: short-term psychodynamic supportive psychotherapy (SPSP), affect phobia therapy (APT) and schema therapy (ST). Although these psychotherapies are commonly used in clinical practice, evidence for the Cluster-C PDs is limited. Additionally, we will investigate predictive factors, non-specific and therapy-specific mediators. METHODS: This is a mono-centre randomized clinical trial with three parallel groups: (1) SPSP, (2) APT, (3) ST. Randomization on patient level will be pre-stratified according to type of PD. The total study population to be included consists of 264 patients with Cluster-C PDs or other specified PD with mainly Cluster-C traits, aged 18-65 years, seeking treatment at NPI, a Dutch mental health care institute specialized in PDs. SPSP, APT and ST (50 sessions per treatment) are offered twice a week in sessions of 50 min for the first 4 to 5 months. After that, session frequency decreases to once a week. All treatments have a maximum duration of 1 year. Change in the severity of the PD (ADP-IV) will be the primary outcome measure. Secondary outcome measures are personality functioning, psychiatric symptoms and quality of life. Several potential mediators, predictors and moderators of outcome are also assessed. The effectiveness study is complemented with a cost-effectiveness/utility study, using both clinical effects and quality-adjusted life-years, and primarily based on a societal approach. Assessments will take place at baseline, start of treatment and at 1, 3, 6, 9, 12, 18, 24 and 36 months. DISCUSSION: This is the first study comparing psychodynamic treatment to schema therapy for Cluster-C PDs. The naturalistic design enhances the clinical validity of the outcome. A limitation is the lack of a control group for ethical reasons. TRIAL REGISTRATION: NL72823.029.20 [Registry ID: CCMO]. Registered on 31 August 2020. First participant included on 23 October 2020.