Short-term versus long-term mentalization-based therapy for outpatients with subthreshold or diagnosed borderline personality disorder: a protocol for a randomized clinical trial

The short-term MBT program is designed as a 20-week psychotherapy program consisting of five sessions of introductory MBT (MBT-I) followed by 15 sessions of group MBT (MBT-G) accompanied by conjoined individual sessions every second week and two psycho-educative meetings with participants and their relatives. Seven to nine participants and two therapists will be included in each short-term MBT group. The groups are closed to enhance cohesion between group participants. A total of 11 short-term MBT groups will be included in this trial.

Originally, MBT-I was a 12-session introductory psycho-educative program covering relevant topics like personality disorders, attachment, and mentalization [40]. The original manual has been modified for our 5-week intervention. A copy of our modified manual is available upon request. After the completion of MBT-I, the same group of participants will move on to MBT-G, which consists of 15 sessions of mentalization-based psychotherapy in groups, as manualized by Bateman and Fonagy [14]. In our short-term MBT program, group sessions will be accompanied by individual psychotherapy every second week with one of the two group therapists. As part of the individual therapy, a case formulation will be prepared and subsequently shared by the participants in the group. The overall purpose of the individual sessions is for the therapist and participant to develop a consensus of the participant’s main difficulties and to establish psychotherapeutic focus points in the group therapy. Furthermore, participants and relatives will be invited to two psycho-educative meetings hosted by the therapists at the beginning of the treatment program to enhance the mentalization work at home. The participants in the short-term MBT program will furthermore be offered three individual follow-up sessions after the end of treatment.

Long-term MBT is organized as a 14-month program and has been implemented at the clinic for the past 7 years. All participants randomized to long-term MBT will initially enter a 6-week MBT-I program manualized by Karterud and Bateman [40] and modified for our 6-week intervention in collaboration with the authors. New MBT-I groups commence every time new participants are recruited and randomized to long-term MBT. A maximum of 12 participants can enter an MBT-I group. When MBT-I finishes, participants will be allocated to one of eight slow-open MBT treatment groups. MBT-G is then organized as 12 months of weekly group therapy sessions, also manualized by Bateman and Fonagy [14]. In the long-term MBT program, group sessions will be accompanied by combined individual MBT sessions every 2 weeks throughout the program. As part of the individual therapy, a case formulation will be developed and subsequently shared with the group by the participant. Furthermore, participants and relatives will also be invited to two psycho-educative meetings hosted by the therapists to enhance the mentalization work at home. When a participant drops out or completes MBT-G, a new participant can start in the group. This procedure continues until the target sample size has been randomized to the long-term MBT program. The participants in the long-term MBT program will also be offered three individual follow-up sessions after the end of treatment.

Participants who are receiving psychotropic treatment will be allowed to continue their medical treatment while participating in the trial. The medical protocol will follow national as well as international medical recommendations for the treatment of borderline personality disorder and comorbid disorders [39, 41]. Psychiatrists or attending physicians at the clinic will assess the need for additional psychotropic treatment and are asked to adhere to the guidelines. All participants, regardless of treatment condition, will be asked about their current medication by trial personnel during trial interviews to allow us to measure any potential differences in the use of psychotropic medication between the groups.

The primary outcome is the severity of borderline symptomatology assessed with the ZAN-BPD [38], which is a clinician-administered scale for the assessment of change in borderline psychopathology over time. Each of the nine borderline personality disorder criteria are rated on a 0 to 4 anchored scale reflecting the severity of symptoms. The rating is intended to reflect both the frequency and the severity of borderline psychopathology. The interview provides a total score of borderline psychopathology ranging from 0 to 36. ZAN-BPD will be assessed by investigators blind to treatment allocation at baseline, and at the 8-, 16-, and 24-month follow-ups. We will video-record interviews to allow an assessment of inter-rater reliability based on the intraclass correlation coefficient. The results will be evaluated using the guidelines provided by Cicchetti [45].

Functional impairment will be assessed with the Work and Social Adjustment Scale (WSAS) [46, 47]. This self-report scale will be assessed at baseline, and at the 8-, 16-, and 24-month follow-ups. Quality of life will be assessed with the Short-Form Health Survey (SF-36) [48], which consists of a mental and a physical component. We will use the mental component as a secondary outcome and the physical component as an exploratory outcome. This self-report scale will be given at baseline, and at the 8-, 16-, and 24-month follow-ups. Global functioning will be measured with the Global Assessment of Functioning (GAF) split version [49]. GAF will be assessed by investigators blind to treatment allocation at baseline, and at the 8-, 16-, and 24-month follow-ups. Inter-rater reliability will be calculated using the previously mentioned guidelines. Severe self-harm (dichotomous data) will be measured as the proportion of participants with severe self-harm defined as deliberate acts of self-harm resulting in visible tissue damage. Self-harm will be assessed by investigators blind to treatment allocation using the Suicide and Self-harm Inventory (SSHI) (citation) at baseline, and at the 8-, 16-, and 24-month follow-ups.

Symptom distress will be measured with the Global Severity Index (GSI) of the Symptom Checklist 90-R (SCL-90-R) [50]. SCL-90-R will be given at baseline, and at the 8-, 16-, and 24-month follow-ups.

The sample size was determined by the predicted change in the primary outcome measure, ZAN-BPD. A 3.5-point superiority margin is considered to be the minimal important difference. Consistent with previous trials that have used ZAN-BPD as an outcome measure for a patient group like ours [24, 58], we expect a standard deviation of 8. With power set at 80% and alpha set at 5% two-tailed, a sample size of 83 participants is needed in each treatment group, corresponding to a total of 166 participants.

All continuous outcomes will be assessed using linear regression and dichotomous outcomes will be analyzed using logistic regression. The analyses will be based on an intention-to-treat population and will primarily be adjusted for the baseline value of the outcome of interest and the stratification variables used in the randomization. We will secondly adjust all analyses for the following design variables: age (18–30 and 30–60) and functional impairment as assessed with the overall baseline GAF score (0–48 and 49–100) [34].

We will use a five-step procedure [59] to assess if the thresholds for statistical and clinical significance are crossed and we will handle missing data according to the procedure suggested by Jakobsen et al. [60]. A detailed statistical analysis plan will be published before the analyses commence, in which we will provide a detailed description of all primary, secondary, and exploratory analyses. All analyses will be performed blinded with the two intervention groups concealed as A and B.

An external data safety monitoring committee will perform interim analyses when 50% of the data have been collected according to the good clinical practice guidelines of the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use [61]. It will decide whether the trial should stop or carry on. Early stopping criteria will follow the recommendations of Jakobsen et al. [59].