Abstract

Introduction: 

Mentalization-based therapy (MBT) and dialectical behavior therapy (DBT) are effective treatments for cluster B personality disorders (PDs), but few studies have assessed their real-world clinical outcomes in routine practice outside a controlled trial setting.

Methods: 

Our descriptive naturalistic retrospective study evaluated 288 patients with cluster B PDs who predominantly had borderline PD referred to MBT or DBT.

Results: 

Observed changes in emergency department (ED) use and hospitalizations one year before and during the first year of therapy were described for patients with at least one relevant event, along with dropout rates. ED visit analyses concerned 104 patients, and hospitalization analyses concerned 30 patients. Across both treatment modalities, ED visits decreased from 119 in the year prior to treatment to 37 during the first year of treatment (p < .001 for both). Hospitalizations were observed to decrease for patients in MBT (p < .05), while no clear change was seen in the DBT group (p = .595). Drop-out rates during treatment were around 30% in both modalities.

Discussion: 

These patterns descriptively suggest that both therapies are associated with reduced service use during treatment in clinical practice. Future research should investigate which patient- and system-level characteristics can guide patients and clinicians toward the most suitable treatment for everyone, and whether these observed patterns persist beyond the treatment period.

1 Introduction

Cluster B personality disorders (PDs) (borderline, narcissistic, antisocial, and histrionic) represent around 13% of the clinical psychiatric population and roughly 2.5% to 3% of the general population (1, 2). Within this group, borderline personality disorder (BPD) is the most prevalent diagnosis in clinical settings. Cluster B PDs are not only common in both general and clinical populations, but they are also associated with a significantly reduced life expectancy, by approximately 9 years for women and 13 years for men at age 20, primarily due to elevated suicide rates and comorbid physical illnesses (1). People with cluster B PDs are also high health care service users: in one year, 78% of them have consulted a family physician, 62% of them visited a psychiatrist, 44% were admitted into the emergency room, and 22% were hospitalized (1). This vital health care use translates into high treatment costs, ranging from $15,000 USD to $50,000 USD per patient every year (3, 4).

Furthermore, many studies have shown that PDs are often comorbid, particularly with borderline personality disorder (BPD) (2, 5). While studying BPD in isolation through randomized controlled trials helps optimize sample homogeneity and design targeted psychotherapeutic interventions, clinicians in real-world settings must frequently manage significant comorbidity, especially among Cluster B PDs. Furthermore, patients with comorbid PDs tend to have a poorer prognosis and are less likely to achieve complete symptomatic remission (6). Therefore, given the high mortality rates, healthcare service utilization, and unfavorable prognosis for patients with comorbid cluster B PDs, it is essential to study this population as a whole.

Mentalization-based therapy (MBT) and dialectical behavior therapy (DBT) are two evidence-based treatments designed for individuals with borderline PD (7, 8). MBT is grounded in psychodynamic theory and attachment theory, with a specific focus on mentalization (9). DBT is a type of cognitive-behavioral therapy that integrates Eastern mindfulness practices to enhance a person’s ability to regulate distress, accept experiences, and manage interpersonal emotions (10). While meta-analyses have established that these treatments have a moderate effect size (Setkowski et al., 2023), their implementation in real-world clinical settings presents several challenges. Patient populations are more heterogeneous, comorbidities are frequent, and therapists differ in their level of experience and training, especially in managing the clinical complexity of Cluster B PDs. Thus, although their efficacy is well established—and even explored in real-world settings for patients with borderline PD (11)—their efficiency in a broader PD population remains underexplored. Similarly, beyond the documented efficacy of specialized psychotherapies in research settings, treatment dropout has been the subject of numerous studies for borderline PDs (12). However, none have specifically focused on the population of individuals with Cluster B PDs.

In this retrospective, naturalistic study, we examine the outcomes of MBT and DBT as delivered in routine clinical practice for adult patients with predominantly BPD along with other Cluster B PDs. Specifically, we aim to describe pre-post differences of these treatments in a real-world setting by analyzing two key clinical indicators during the first year of therapy: the number of emergency department (ED) visits and psychiatric hospitalizations. These ‘hard outcomes’ are frequently used in the literature to evaluate clinical trajectories, with reductions typically reflecting a more favorable prognosis (11, 13, 14). Additionally, we investigate treatment completion rates by comparing dropout rates before and after the start of therapy. Given the naturalistic design, absence of a control group, and lack of a priori hypotheses, all findings are interpreted as associative and exploratory rather than as evidence of treatment effects or comparative effectiveness.

2 Methods

2.1 Study design and participants

This retrospective, naturalistic, and descriptive study was conducted in a real-world, clinical outpatient setting. We examined adults who have been referred to MBT or DBT from general psychiatrists or the ED after being admitted to the “Service des troubles relationnels et de la personnalité”, which is an outpatient clinic at the Institut Universitaire en Santé Mentale de Montréal, in Quebec, Canada, between January 1st, 2015, and December 31st, 2019. Most participants were diagnosed with at least one cluster B PD as their primary diagnosis. In some cases, patients with a PD not otherwise specified (NOS) or PD traits as their primary diagnosis were also admitted if it caused them significant distress or daily life dysfunction. The study’s population consisted of 363 participants, among whom 75 had dropped out before entering treatment modalities and were excluded from further analysis. The final treatment cohort consisted of 288 patients, which was used for descriptive analyses of treatment dropout following initiation. Analyses of emergency department visits and hospitalizations were further restricted to subgroups of patients who presented with at least each respective event in the observation period. All patient data were extracted from the DATA Bank, which includes all voluntary patients admitted to the outpatient clinic. Both the data bank and this specific study were reviewed and approved by the Research Ethics Board of the CIUSSS de l’Est-de-l’Île-de-Montréal., with which the Institut Universitaire en Santé Mentale de Montréal is affiliated, and the procedures followed were by the Helsinki Declaration as revised in 2013. Written informed consent for the use of clinical data was obtained from patients at admission, and the ethics board waived the requirement for additional consent specific to this retrospective analysis.