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Eur J Psychotraumatol
Eur J Psychotraumatol
European Journal of Psychotraumatology
2000-8066
Taylor & Francis

39221987
2393061
10.1080/20008066.2024.2393061
Version of Record
Clinical Research Article
Research Article
Long-term effects of dialectical behaviour therapy for posttraumatic stress disorder and cognitive processing therapy 9 months after treatment termination
Efectos a largo plazo de la terapia dialéctica conductual para el trastorno de estrés postraumático y la terapia de procesamiento cognitivo 9 meses después de la finalización del tratamientoEUROPEAN JOURNAL OF PSYCHOTRAUMATOLOGY
R. VONDERLIN ET AL.
Vonderlin Ruben a
Priebe Kathlen b
Müller-Engelmann Meike cd
Fydrich Thomas e
Steil Regina c
Resick Patricia A. f
Schmahl Christian a
Lindauer Petra g
Kleindienst Nikolaus a
Bohus Martin ah
a Department of Psychosomatic Medicine and Psychotherapy, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany
b Department of Psychiatry and Psychotherapy, Charité-Universitätsmedizin Berlin, Berlin, Germany
c Institute of Psychology, Goethe University Frankfurt am Main, Frankfurt, Germany
d Department Psychology, Medical School Hamburg, Hamburg, Germany
e Department of Psychology, Faculty of Life Sciences, Humboldt University, Berlin, Germany
f Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC, USA
g Department of Economics and Media, Hochschule Fresenius University of Applied Sciences, Cologne, Germany
h McLean Hospital, Harvard Medical School, Boston, MA, USA
CONTACT Ruben Vonderlin ruben.vonderlin@zi-mannheim.de Department of Psychosomatic Medicine and Psychotherapy, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Germany
* Authors contributed equally

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© 2024 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
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https://creativecommons.org/licenses/by-nc/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent.

ABSTRACT

Background: The complexity of posttraumatic stress disorder (PTSD) symptoms related to childhood abuse (CA) present challenges for effective psychotherapeutic treatment. Consequently, there is great interest in the long-term effectiveness of psychological treatments for this population.

Objective: This study aims to investigate the long-term outcomes of Dialectical Behaviour Therapy for PTSD (DBT-PTSD) and Cognitive Processing Therapy (CPT) 9 months after treatment termination.

Method: This is a long-term analysis from a randomised-controlled trial of DBT-PTSD versus CPT (registration number DRKS00005578). Initially, 193 individuals with CA-related PTSD were randomly allocated to receive either DBT-PTSD (n = 98) or CPT (n = 95). The primary outcome the Clinician-administered PTSD-Scale for DSM-5 (CAPS-5) was administred at baseline, treatment completion (15 months post-randomization) and at the 9-month follow-up. Secondary outcomes included self-reported PTSD severity (PCL-5), dissociation (DSS), severity of borderline symptoms (BSL-23), and psychosocial functioning (GAF).

Results: No significant changes were observed in the primary (CAPS) and all other outcomes from post-intervention to 9-months follow-up in both the DBT-PTSD (CAPS: Mpost  = 15.60, Mfollow-up  = 14.93) and CPT group (CAPS: Mpost = 18.80, Mfollow-up = 17.41). Between-group analyses at 9-months follow-up were significantly in favour of DBT-PTSD compared to CPT with small to medium effect sizes on all outcomes ranging from d = 0.35 on the CAPS to d = 0.57 on the BSL-23 and GAF.

Conclusions: Our results indicate that treatment effects of psychotherapy addressing complex presentations of PTSD persist 9 months after treatment termination. In addition, the superiority of DBT-PTSD as compared to CPT found at treatment termination, was confirmed at 9-months follow-up.

Trial registration: German Clinical Trials Register identifier: DRKS00005578..

HIGHLIGHTS

This study investigates the long-term effects of Dialectical Behaviour Therapy for Posttraumatic Stress Disorder (DBT-PTSD) and Cognitive Processing Therapy (CPT) on complex presentations of PTSD 9 months after treatment termination.

In both treatment arms, treatment effects persisted over 9 months post-treatment termination across a wide range of outcomes.

DBT-PTSD showed significant superiority over CPT at 9 months follow-up with differential effect sizes between d = 0.35 and d = 0.57.

Antecedentes: La complejidad de los síntomas del trastorno de estrés postraumático (TEPT) relacionados con el maltrato infantil (CA, en sus siglas en inglés) presenta retos para un tratamiento psicoterapéutico efectivo. En consecuencia, existe un gran interés en la efectividad a largo plazo de los tratamientos psicológicos para esta población.

Objetivo: Este estudio tiene como objetivo investigar los resultados a largo plazo de la Terapia Dialéctica Conductual para el TEPT (DBT-PTSD) y la Terapia de Procesamiento Cognitivo (CPT, en sus siglas en inglés) 9 meses después de la finalización del tratamiento.

Método: Se trata de un análisis a largo plazo de un ensayo controlado aleatorizado de DBT-PTSD frente a CPT (número de registro DRKS00005578). Inicialmente, 193 individuos con TEPT relacionado con CA fueron asignados aleatoriamente para recibir DBT-PTSD (n=98) o CPT (n=95). El resultado primario fue la Escala de TEPT administrada por el clínico del DSM-5 (CAPS-5), que se administró al inicio, al final del tratamiento (15 meses después de la aleatorización) y en el seguimiento de 9 meses. Los resultados secundarios incluyeron la gravedad del TEPT autoinformada (PCL-5), la disociación (DSS), la gravedad de los síntomas limítrofes (BSL-23) y el funcionamiento psicosocial (GAF).

Resultados: No se observaron cambios significativos en el resultado primario (CAPS) y en todos los demás resultados desde el período posterior a la intervención hasta los 9 meses de seguimiento, tanto en el grupo DBT-PTSD (CAPS: M posterior =15,60, M seguimiento =14,93) como en el grupo CPT (CAPS: M posterior =18,80, M seguimiento =17,41). Los análisis entre grupos a los 9 meses de seguimiento fueron significativamente favorables a la DBT-PTSD en comparación con la CPT, con tamaños del efecto de pequeños a medianos en todos los resultados, desde d =0,35 en la CAPS hasta d =0,57 en la BSL-23 y el GAF.

Conclusiones: Nuestros resultados indican que los efectos del tratamiento de la psicoterapia que aborda las presentaciones complejas del TEPT persisten 9 meses después de la finalización del tratamiento. Además, la superioridad de DBT-PTSD en comparación con CPT encontrada al finalizar el tratamiento, se confirmó a los 9 meses de seguimiento.

KEYWORDS

Long-term
childhood abuse
posttraumatic stress disorder
psychotherapy
treatment
DBT-PTSD
CPT
PALABRAS CLAVE

A largo plazo
abuso infantil
trastorno de estrés postraumático
psicoterapia
tratamiento
DBT-PTSD
CPT
German Federal Ministry for Education and Research BMBF 01KR1303A This work was supported by the German Federal Ministry for Education and Research [grant number BMBF 01KR1303A].
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pmc1. Introduction

Childhood abuse (CA) is a prevalent and profoundly distressing experience that can leave enduring psychological scars and severe long-term impairment for those affected (Fergusson et al., 2008; Tsang et al., 2021). Prevalence estimates of CA indicate that approximately 8% of male children and 18–20% of female children experience sexual abuse (Pereda et al., 2009; Stoltenborgh et al., 2011), while the prevalence rates of physical and emotional abuse are estimated to be even higher (23% for physical abuse; 36% for emotional abuse) (Stoltenborgh et al., 2015). CA is associated with a numerous negative clinical conditions including an increased risk of developing emotion dysregulation and psychiatric disorders such as posttraumatic stress disorder (PTSD) (Dvir et al., 2014; Messman-Moore & Bhuptani, 2017). Compared to persons with other forms of traumatic events, survivors of CA often show more complex presentations of symptoms, including chronic suicidality, impulsivity, higher general dysfunction and the occurrence of hospitalisation (Zlotnick et al., 2003), dissociation (Vonderlin et al., 2018), substance abuse (Sanders et al., 2018), depressive symptoms, psychotic symptoms or somatic complaints (Nalavany et al., 2009).

The complex presentations of PTSD associated with CA, pose significant challenges for effective psychological therapies. A meta-analysis by Karatzias et al. (2014) highlighted the importance of CA and complex PTSD symptoms in predicting suboptimal outcomes within trauma-related psychotherapy. This finding has generated controversy regarding the most appropriate approach to address the specific needs of individuals with CA-related PTSD.

Most treatment guidelines for the treatment of PTSD advocate for trauma-focused therapies such as Prolonged Exposure, Cognitive Processing Therapy (CPT), or trauma-focused Cognitive–behavioural Therapy (CBT) (Berliner et al., 2019; Curtois et al., 2017). Nevertheless, there is an ongoing discussion on the adequacy of these established treatment modalities in effectively addressing CA-related PTSD (De Jongh et al., 2016). Authors in the field propose different perspectives on this issue, with some advocating ‘phase-based treatments’ (Cloitre et al., 2002) that prioritise emotion regulation before focusing on traumatic memories (Cloitre et al., 2002; Cloitre et al., 2010; Harned et al., 2018; Rosner et al., 2019). Conversely, others believe that traditional trauma programmes are adequately equipped to handle these cases without additional components (De Jongh et al., 2016; Foa et al., 2005; Resick et al., 2008). Currently, there is insufficient evidence to determine which therapeutic approach is more suitable for complex presentations of PTSD, because RCTs directly comparing the two treatment approaches remain scarce. This ongoing discourse underscores the critical need to investigate potential benefits of specific treatments that are tailored to the treatment of CA-related PTSD.

Dialectical Behaviour Therapy for PTSD (DBT-PTSD) is a treatment developed specifically to address the needs of individuals with CA-related PTSD combining principles and interventions of dialectical behaviour therapy and CBT (Bohus et al., 2019). After showing its feasibility and safety under residential conditions (Bohus et al., 2013), the efficacy of this new tailored treatment was investigated under outpatient conditions in a multicenter randomised controlled trial. The trial compared DBT-PTSD with CPT, a well-established and evidence-based PTSD treatment (Bohus et al., 2020; Resick et al., 2016). The results of this study showed large and statistically significant improvements in PTSD severity for individuals in both groups, those who received DBT-PTSD and those who received CPT. Notably, the improvement observed in the DBT-PTSD group exceeded that of the CPT group. ITT analyses revealed symptomatic remission in 58% of individuals in the DBT-PTSD group and 41% of individuals in the CPT group so that they no longer met diagnostic criteria for PTSD after therapy (Bohus et al., 2020).

While these findings provide empirical evidence for the immediate effects of CA-related PTSD treatment, our understanding of the long-term effects of these interventions is more limited. In a meta-analysis investigating long-term effects of psychological treatments for PTSD, only five out of 32 included studies addressed populations with CA-related PTSD (Kline et al., 2018). The complexity and chronicity of symptoms in this population prior to treatment initiation raise the question of how symptoms develop after treatment termination.

Previous research on the long-term effects of trauma-focused treatments for CA-related PTSD has been mixed and mostly limited to pilot and feasibility studies. In a feasibility study of N = 45 individuals with PTSD and Borderline Personality Disorder (BPD), Kolthof et al. (2022) investigated the long-term effects of a high-intensity PTSD treatment consisting of 90 min Prolonged Exposure (PE) and 90 min Eye-Movement-Desensitization-Reprocessing (EMDR) per day over 8 days (two periods of 4 days). They found that PTSD symptoms decreased significantly from pre- to post-treatment (d = 1.58). This effect deteriorated at the 6-month follow-up (d = 1.20; i.e. PTSD symptoms increased, although still a large effect size), but was restored at the 12-month follow-up (d = 1.53). However, the decrease in PTSD symptoms from 6 to 12 months did not reach significance.

In another pilot study, Niwa et al. (2022) examined the effect of Narrative Therapy (a trauma-focused treatment based on PE) that was tailored for complex presentations of PTSD by adding individual skills-training for emotion and interpersonal regulation. They allowed a maximum of 25 sessions of which the first 8 sessions focused on skills-teaching. The study encompassed a cohort of N = 10 individuals who met the criteria for complex PTSD (cPTSD). The analysis revealed a significant effect from pre- to post-treatment (d = 1.06), indicating a noteworthy improvement in the measured outcome. Encouragingly, this positive trend persisted, albeit not significantly, over a 3-month follow-up period, with the effect size slightly increasing to d = 1.22.

In a large study by Resick et al. (2002), CPT and PE were compared with a minimal attention waiting condition group, demonstrating efficacy in treating chronic PTSD among female rape victims. Both CPT and PE showed substantial effect sizes compared to the minimal attention waiting condition in the intent-to-treat sample at post-intervention, with g = 0.74 (PE) and g = 0.97 (CPT) on the CAPS. Effect sizes in the completer sample were even higher, with g = 2.05 (PE) and g = 2.78 (CPT) compared to the minimal attention waiting condition. These positive treatment effects were sustained throughout follow-up assessments at 3 and 9 months, and remarkably, persisted over longer periods, as evidenced by re-assessments conducted 5 to 10 years later (M = 6.15 years) (Resick et al., 2012). Further insights from Resick et al. (2003) revealed consistent treatment effects of CPT and PE comparing childhood sexual abuse (CSA) survivors versus those without CSA history, suggesting no differential efficacy between these distinct patient populations on complex PTSD symptoms. These longer-term findings are corroborated by Bass et al. (2022), who demonstrated enduring efficacy of CPT even 6 years post-treatment among survivors of sexual violence, although their study did not specifically focus on childhood abuse survivors.

Expanding on the efficacy of CPT in treating PTSD following sexual assaults, Chard (2005) investigated the long-term effects of CPT adapted for survivors of childhood sexual abuse (CPT-SA). They included 76 PTSD individuals with a history of sexual abuse and compared CPT-SA against a minimal-attention wait-list control group. They found that improvements from pre- to post-treatment significantly increased by 3 months follow-up and extended by 1 year of follow-up.

A similar pattern was found by Cloitre et al. (2002) who investigated an adapted form of PE following affective and interpersonal regulation skills group (STAIR modified PE) against a minimal attention wait-list group in 46 individuals meeting PTSD criteria after sexual or physical abuse. They showed that improvements of the active therapy significantly continued from post- to 3-month follow-up and even further improved from 3-month to 9-month follow-up.

Taken together, previous research indicates that positive effects of psychotherapy focusing on CA-related PTSD extend beyond the end of treatment. However, most of these studies investigated long-term effects within a single-armed trial or investigated treatments against a waitlist control group. As a result, there is a lack of evidence examining whether a tailored treatment for CA-related PTSD has different long-term effects than a well-established evidence-based PTSD treatment.

The overall aim of the present study was to expand our understanding of the long-term effectiveness of CA-related PTSD treatment beyond short-term symptom reduction. Specifically, we aimed to (i) analyse whether the treatment effects of psychotherapy for CA-related PTSD extend 9 months after the end of treatment and (ii) compare a tailored treatment for CA-related PTSD (DBT-PTSD) with a well-established PTSD intervention (CPT) in the long term.

2. Methods

Data were derived from a psychotherapy trial comparing Dialectical Behavioural Therapy for Posttraumatic Stress Disorder (DBT-PTSD) (Bohus et al., 2019, 2020), which was developed specifically to treat complex representations of PTSD following childhood abuse, with Cognitive Processing Therapy (CPT) (Resick et al., 2016). The study was conducted at three sites in Germany (Mannheim, Berlin, Frankfurt) and was registered in the German Clinical Trials Register (DRKS00005578) and approved by the ethical review committees at each site.

As described previously (Bohus et al., 2019, 2020), participants were recruited from the waiting lists of the three German outpatient clinics mentioned above, from advertisements, and from therapists who were made aware of the study. Women who were 18 to 65 years old at study entry, and who had been diagnosed with PTSD (according to DSM-5 criteria) after sexual or physical abuse before the age of 18 years were included. In addition, participants were required to fulfil at least three BPD criteria according to DSM-5, including criterion 6 (i.e. affective instability). Furthermore, they were required to commit availability for one year of outpatient treatment. Exclusion criteria included lifetime diagnoses of schizophrenia, bipolar I disorder, mental retardation, or severe psychopathology requiring immediate treatment in a different setting (e.g. a body mass index below 16.5); life-threatening suicide attempts within the last 2 months; current substance dependence (any use within the last 2 months); medical conditions contradicting exposure protocol (e.g. pregnancy); a highly unstable life situation (e.g. homelessness); scheduled residential treatment; and receipt of either CPT or DBT-PTSD treatment during the last year (Bohus et al., 2019, 2020). In order to improve external validity, individuals were not excluded for ongoing self-harm, suicidality, or high-risk behaviours.

Participants underwent a 15-month outpatient treatment, consisting of weekly individual therapy sessions (50 min each) for the initial 12 months. In the concluding three months, participants received three booster sessions. After this 15-month period, the treatment was terminated. If participants wished to receive further therapeutic support, they were allowed to arrange it independently. Importantly, the protocol prohibited the continuation of treatment with the same therapist. Continuation of therapy with another therapist in the same facility was permitted. A more detailed description of the treatment contents can be found in Bohus et al. (2019).

As depicted in the flow chart (Figure 1), N = 955 individuals were screened for eligibility. Of those, n = 200 individuals were included in the study and randomised to either receive DBT-PTSD (n = 103) or CPT (n = 97). Of the 200 randomised individuals, 7 had to be excluded because of violation of inclusion and exclusion criteria (e.g. no PTSD (n = 3), schizophrenia, pregnancy, brain tumour or not female sex, each n = 1). This left us with a final sample of 98 participants in DBT-PTSD and 95 participants in CPT. In the DBT-PTSD group, 25 individuals discontinued treatment (26%); in the CPT group, 37 participants discontinued treatment (39%). In both groups, 8 participants did not provide assessments at post-intervention and were only included in the intent-to-treat analyses (ITT), but not in the analyses according to protocol (ATP). Thus, 65 participants in the DBT-PTSD group and 50 participants in the CPT group were included in the ATP analysis at post-intervention. At 9-months follow-up, 11 participants in the DBT-PTSD group and 7 participants in the CPT group did not provide data and were excluded from the ATP analyses. Thus, 62 participants in the DBT-PTSD group and 51 participants in the CPT group were included in the ATP analysis at follow-up. The ITT sample consisted of all participants who have been randomised and not excluded due to protocol violation, consisting of 98 participants in the DBT-PTSD and 95 participants in the CPT group. Figure 1. Participants flow chart. The flow chart shows the progression of participants throughout the study.

Note: DBT-PTSD: Dialectical Behaviour Therapy for Posttraumatic Stress Disorder; CPT: Cognitive Processing Therapy; ATP: completed According to Protocol; ITT: intent-to-treat analysis.

The predefined primary outcome was the CAPS-5 (Clinical Administered PTSD Scale for DSM-5 Weathers et al., 2018; German version Müller-Engelmann et al., 2020) to assess PTSD severity. In addition, we used the PCL-5 as self-report instrument to assess PTSD symptoms (Blevins et al., 2015); German version (Krüger-Gottschalk et al., 2017). To assess difficulties in affect regulation, self-concept, and interpersonal relationships, we used the Borderline Symptom List (BSL-23; Wolf et al., 2009). Because individuals with a history of CA often report elevated levels of dissociative symptoms, we used the Dissociative Symptom Scale (DSS; Stiglmayr et al., 2010). Depressive Symptoms were assessed using the Beck Depression Inventory-II (BDI-II; Beck et al., 1996) and psychosocial functioning with the Global Assessment of Functioning (GAF) according to DSM-IV.

To analyse and characterise the development of symptoms during the follow-up period, we used the following statistical methods: first, we conducted within-group comparisons of post-treatment (month 15) and follow-up assessments (month 24) in both treatment groups to test for potential changes within both treatment groups. Second, we calculated Pearson correlation coefficients between post and follow-up scores in both treatment groups to quantify the stability of participants’ outcomes in each group from post to follow-up. Third, we used graphical plots to visualise the effects of individual participants by plotting post-assessment scores on the x-axis, against follow-up assessments on the y-axis and including a reference line indicating reliable effects. Reliable change was defined as exceeding the threshold of SD∗2∗1−reliability∗1.96 (Christensen, 1986). Because the primary goal of these analyses was to analyse how treatment effects develop during follow-up after treatment completion, we applied this analysis to the according to protocol (ATP) sample only. ATP was defined as participants who completed treatment according to protocol.

To analyse differential effects in DBT-PTSD vs. CPT, we compared the follow-up mean scores of both groups using independent sample t-tests. Because participants in the DBT-PTSD group tended to have higher standard estimations (SDs), we used a Welch’s two-sample t-test (Derrick et al., 2016). This analysis was based on the ITT sample, because dropout rates varied significantly between treatment groups and would lead to a differential attrition bias when analysing the ATP sample. As described previously (Bohus et al., 2020), imputation of missing data was aiming at minimising bias while maximising efficiency. Accordingly, item-level imputation, was preferred over scale-level imputation when no more than single items were missing (Gottschall et al., 2012). In this case (i.e. less than 10% of missing items) a Stochastic Regression Imputation approach which avoids overfitting (Enders, 2006) was used. Otherwise, multiple imputation applying the Markov chain Monte Carlo (MCMC) method was used (Rubin, 1996; Schafer, 1997). Multiple imputation was based on the scale-level values of other assessment points, the drop-out status (yes/no) and the allocated group were used for imputation. The (two-sided) alpha-level was set at .05.

3. Results

In both treatment groups the CAPS-5 scores at post-treatment and at follow-up assessment showed no significant within-group changes in the ATP sample (DBT-PTSD: Mpost = 15.60, SD = 14.78; Mfollow-up = 14.93, SD = 15.78; t(57)=0.61, p = .546; d = 0.08; CPT: Mpost = 18.80, SD = 15.33; Mfollow-up = 17.41, SD = 14.14; t(45) = 0.86, p = .396; d = 0.13). This was also true for all secondary outcomes (all ps > 0.77; see Table 1). Effect sizes on other outcomes ranged from d = −0.25 on the PCL-5 to d = 0.25 on the BDI-II in the DBT-PTSD group and from d = −0.08 on the PCL-5 to d = 0.21 on the GAF in the CPT group. Intercorrelations from post to follow-up assessments were high in both groups ranging from r = 0.66 on the BSL behavioural items to r = 0.94 on the dissociation intensity scale of the DSS in the DBT-PTSD group, and from r = 0.76 on the dissociation intensity scale of the DSS to r = 0.86 on the BDI in the CPT group. Table 1. Outcomes of participants randomised to DBT-PTSD or CPT at baseline, post-intervention and Follow-up.

 	Mean (SD), ATP	t-test and effect size (Cohen d) within group, ATP	Pearson Correlation Coefficient within group, ATP	t-test and effect size (Cohen d) between group, ITT	
Measure	Baseline	Post	Follow-Up	Post to Follow-Up	Post to Follow-Up	Follow-Up	
Clinician Administered PTSD Scale	 	 	 	 	 	 	
DBT-PTSD	39.25 (11.01)	15.60 (14.78)	14.93 (15.78)	t(57) = 0.61, p = .546; 0.08	0.88, p < .001	t(190.2) = 2.41, p = .017; 0.35	
CPT	40.03 (7.86)	18.80 (15.33)	17.41 (14.14)	t(45) = 0.86, p = .396; 0.13	0.79, p < .001	
Posttraumatic Stress Disorder Checklist for DSM-5	 	 	 	 	 	 	
DBT-PTSD	49.31 (11.13)	17.20 (15.37)	17.74 (15.98)	t(52) = −1.80, p = .077; −0.25	0.87, p < .001	t(188.4) = 3.61; p < .001; 0.52	
CPT	48.20 (10.57)	23.71 (19.46)	23.57 (20.37)	t(36) = −0.47, p = .641; −0.08	0.77, p < .001	
Dissociation Tension Scale -Duration	 	 	 	 	 	 	
DBT-PTSD	24.09 (16.55)	10.89 (16.78)	10.54 (14.55)	t(44) = 0.63, p = .530; 0.09	0.89, p < .001	t(180.5) = 3.01; p = .003; 0.43	
CPT	20.31 (13.28)	14.52 (19.47)	13.61 (16.55)	t(33) = 0.09, p = .930; 0.01	0.81, p < .001	
Dissociation Tension Scale – Intensity	 	 	 	 	 	 	
DBT-PTSD	2.79 (1.77)	1.37 (1.95)	1.38 (1.70)	t(40) = 0.19, p = .850; 0.03	0.91, p < .001	t(188.9) = 2.74; p = .007; 0.40	
CPT	2.77 (1.55)	1.92 (2.13)	1.82 (1.81)	t(32) = −0.09, p = .926; 0.02	0.76, p < .001	
Borderline-Symptom List-23	 	 	 	 	 	 	
DBT-PTSD	1.98 (0.78)	0.95 (0.94)	0.91 (0.83)	t(51) = −0.14, p = .889; −0.02	0.80, p < .001	t(186.4) = 3.94; p < .001; 0.57	
CPT	1.97 (0.81)	1.27 (1.08)	1.15 (0.94)	t(36) = 1.08, p = .289; 0.17	0.83, p < .001	
Borderline Symptom List – behavioural items	 	 	 	 	 	 	
DBT-PTSD	0.33 (0.30)	0.11 (0.17)	0.14 (0.20)	t(51) = −1.24, p = .220;	0.66, p < .001	 	
CPT	0.29 (0.27)	0.19 (0.26)	0.19 (0.26)	t(36) = −0.32, p = .754;	0.83, p < .001	 	
Beck Depression Inventory	 	 	 	 	 	 	
DBT-PTSD	35.88 (11.16)	18.95 (15.63)	17.02 (14.41)	t(41) = 1.79, p = .080; 0.25	0.86, p < .001	t(190.4) = 3.14; p = .002; 0.45	
CPT	35.06 (12.81)	21.42 (17.48)	19.49 (14.47)	t(35) = 0.78, p = .442; 0.13	0.86, p < .001	
Global Assessment of Functioning	 	 	 	 	 	 	
DBT-PTSD	50.78 (9.01)	64.28 (13.96)	66.25 (13.96)	t(53) = −0.80, p = .428; 0.11	0.80, p < .001	t(190.8) = −3.88; p < .001; −0.56	
CPT	50.12 (7.62)	61.21 (12.13)	61.55 (13.93)	t(44) = −1.43, p = .161; 0.21	0.84, p < .001	 	
Note: Within-group t-tests represent stabilisation of effects from Post-intervention to Follow-Up. Between-group t-tests were conducted to analyse effects between groups at Post-intervention and Follow-Up in the According to Protocol Sample (ATP) as well as the intent to treat sample (ITT).

Visual inspection of individual participant data in the plots indicated that most participants showed no reliable changes in their symptoms from post-intervention to 9-months follow-up. However, there were also a number of participants showing reliable improvement or deterioration (see Figure 2). On the CAPS, from 104 participants completing treatment according to protocol, most participants (72%, n = 75) showed no reliable changes during the follow-up. However, 11% (n = 10) showed reliable deterioration from post to follow-up assessments, whereas 17% (n = 18) showed reliable improvement. As shown in Figure 2, this pattern was similar for all other outcomes. Figure 2. Outcomes of participants randomised to dialectical behavioural therapy for posttraumatic stress disorder (DBT-PTSD, A) or cognitive processing therapy (CPT, B) (According to Protocol Sample) at the end of therapy vs 9-months Follow-up. Values below the main diagonal indicate improvements; the dotted diagonals represent reliable change.

Comparison of mean scores between DBT-PTSD and CPT at 9-months follow-up showed a significant effect in favour of DBT-PTSD on the CAPS as primary outcome in the ITT sample (MDBT-PTSD = 18.96, SD = 15.89; MCPT = 24.23, SD = 14.44; t(190.2) = 2.41, p = .017) with a small between-group effect-size of d = 0.35 (see Figure 3). This superiority of DBT-PTSD over CPT was more pronounced on all other secondary outcomes with small to medium effect sizes (ps < .05) ranging from d = 0.40 on the DSS to d = 0.57 on the BSL-23 and GAF (see Table 1). Figure 3. Course of mean CAPS scores in the ITT sample in the DBT-PTSD and CPT group at Baseline, Post-Intervention (15months) as well as 9-months follow-up. Error Bars represent 95% confidence intervals using bootstrapping method.

Note: DBT-PTSD: Dialectical Behaviour Therapy for Posttraumatic Stress Disorder; CPT: Cognitive Processing Therapy; ***p < .001; **p < .01; *p < .05; ns: not significant.

4. Discussion

We examined the long-term efficacy of an outpatient psychotherapy programme specifically designed for individuals suffering from CA-related PTSD (DBT-PTSD) and of a well-established evidence-based PTSD treatment (CPT). First, we analysed the stability of both treatment effects from post-intervention to 9-month follow-up. Results showed no significant further changes in symptoms on any outcome during the 9-month follow-up period. High intercorrelations of post and follow-up scores ranging from r = 0.66 on the BSL behavioural items to r = 0.94 on the dissociation intensity scale indicate that participants’ outcomes remain generally stable during the follow-up period. As observed, participants who showed low levels of psychopathology after treatment tended to maintain a similarly low level during the follow-up period. Similarly, those with high levels of psychopathology post-treatment were more likely to persist at a heightened level during the follow-up assessment. Second, we compared both treatments (DBT-PTSD vs. CPT) at the 9-month follow-up. This analysis confirmed the findings from post-intervention, showing larger effect sizes for DBT-PTSD after 24 months, on all outcomes with small to medium between-group effect sizes ranging from d = 0.35 to d = 0.57 (Bohus et al., 2020).

Regarding the stability of effects after treating CA-related PTSD, our results are largely consistent with previous studies showing that positive treatment effects of CA-related PTSD extend after treatment completion up to 12 months follow-up (Chard, 2005; Cloitre et al., 2002; Kolthof et al., 2022; Niwa et al., 2022). Particularly taking into account the chronicity and complexity of symptoms of this group of patients (Maercker et al., 2022), these results indicate that psychotherapy is effective in improving patients’ lives sustainably.

Although most participants’ symptoms remained stable from post-treatment to follow-up, some participants showed reliable changes in symptoms. This was especially pronounced for the BSL-23 symptoms, in which approximately 19% of participants showed reliable higher follow-up scores compared to post-intervention, but approximately 31% of participants showed further improvement during the follow-up period. This is in line with other findings from the PTSD literature, e.g. Foa et al. (2005), who found that the vast majority of participants (79.8%) showed stable PTSD symptoms from post-intervention up to 12 months follow-up, a minority (12.4%) showed reliable improvement during follow-up, but a rather small group (7.9%) showed reliable worsening of symptoms. When comparing our results with findings from DBT trials, a current meta-analytic review investigating long-term follow-ups of DBT, indicates that some studies show significant further improvements from post to follow-up for self-harm (Wetterborg et al., 2020), anger, depression, interpersonal functioning (McMain et al., 2012), and psychosocial functioning (Fassbinder et al., 2007; Kröger et al., 2006), whereas other studies did not (Gillespie et al., 2022). It has been assumed that these further improvements result from successfully coping with further crisis situations and successfully using emotion regulation skills during everyday life after treatment has ended (Gillespie et al., 2022). Our results indicate that these improvements can also be found, at least for some individuals in our PTSD sample. One explanation might be that participants show further reductions in their avoidance behaviour during their everyday life after treatment. However, future research should specifically address this issue by shedding light on factors that predict further individual symptom improvement or deterioration during the follow-up period after the treatment is completed. Knowledge of this may be useful in the design of individualised relapse prevention interventions for individuals who are at high risk of relapse after treatment completion. Potentially useful interventions to prevent symptom recurrence include low-dose booster sessions or app-based low-dose interventions during follow-up (Wilks et al. 2021).

Regarding the comparison between treatment groups (DBT-PTSD vs. CPT), effect sizes at 9-month follow-up are consistent with those found post-intervention, demonstrating larger effect sizes of DBT-PTSD over CPT (Bohus et al., 2020). Interestingly, similar effect sizes were observed on proximal outcomes, such as PTSD or BPD symptoms, e.g. the CAPS effect sizes at post-intervention (d = 0.33) aligning closely with those at follow-up (d = 0.35). Notably, the superiority of DBT-PTSD became more pronounced at follow-up concerning more distal outcomes, including depression or psychosocial functioning. For instance, the between-group effect size on the GAF increased from d = 0.26 at post-intervention to d = 0.56 at follow-up. A potential explanation for these results may be attributed to the treatment structure. DBT-PTSD strategically combines exposure-based techniques with positive psychology elements to empower individuals in building a life worth living. This includes fostering skills such as mindfulness, clarifying values, and setting goals. Notably, the final phase of treatment explicitly emphasises the seamless integration of these acquired skills into individuals’ daily lives, which can help to ensure that these skills continue to be practiced and refined post-termination, supporting further changes after formal treatment ends. In addition, DBT-PTSD as a phase-based treatment comprises a preparation phase in which distress-tolerance and emotion regulation skills are delivered, which can be later help to increase the effectiveness of exposure-based techniques (e.g. by interrupting dissociative states or counteracting the avoidance of trauma-related emotions).

The study's primary strengths lie in its robust examination of long-term effects, conducted 9 months post-treatment completion, through a comprehensive comparison of PTSD treatments within a randomised controlled trial. However, several limitations should be considered when interpreting the data. First, the follow-up period of 9 months is relatively short. Particularly in assessing quality-of-life measures and psychosocial functioning, extending the follow-up duration would be valuable for a more comprehensive understanding of the lasting impact on participants’ lives. Second, we did not assess data on further treatments or psychosocial help offered during the follow-up period. Thus, the stabilisation of treatment effects could be confounded by other interventions and not fully and causally related to the intervention. In particular, participants who may have deteriorated during the follow-up period may have sought additional help, which would lead to an underestimation of deterioration in our sample. Future research is needed to investigate whether such measures are effective in preventing relapse in individuals with complex PTSD. Furthermore, as already stated in Bohus et al. (2020), the effects of allegiance cannot be completely ruled out. Accordingly, the findings require replication from an independent research group. As previously mentioned, the treatment developers were also part of the consultation teams, while in the CPT arm, the supervisors were experienced in cognitive behaviour therapy but did not have more experience in CPT than the therapists (Bohus et al., 2020). Finally, our findings may not be readily generalisable to populations other than women with CA-related PTSD with severe problems in emotion regulation and further symptoms of BPD (Bohus et al., 2020).

In conclusion, our findings suggest that the positive effects of psychological interventions targeting complex presentations of PTSD endure for up to 9 months post-treatment. DBT-PTSD demonstrated significantly greater effectiveness compared to CPT, particularly in addressing borderline-specific symptoms and enhancing psychosocial functioning. These results offer valuable insights for researchers and clinicians, guiding them on effective approaches to treat this population.

Statement of ethics

Please address the following aspects in your Statement of Ethics.

Study approval statement: This study protocol was reviewed and approved by the applicable ethics committees at each study centre, Medical Faculty Mannheim at Heidelberg University in Mannheim, Goethe University in Frankfurt, and Humboldt University in Berlin, approval number of the leading committee [2013-635N-MA].

Consent to participate statement: Written informed consent was obtained from all participants to participate in the study.

Acknowledgements

We acknowledge the contribution and support of the staff at the study coordinating centre and at the participating study sites, including Angelika Spohn, MSc, Katrin Häussler, MSc, Nora Lohse, Dr rer nat, Sophie Rausch, Dr sc hum, Frank Enning, MD, Christopher Hahn, Julia Herzog, Dr sc hum, Nadine Defiebre, MSc, Saskia Hensel, MSc, Martin Jungkunz, Dr phil, Yvonne Scharf, Department of Psychosomatic Medicine and Psychotherapy, Central Institute of Mental Health Mannheim, Medical Faculty Mannheim, Heidelberg University; Klara Lieberz, Dr rer nat, Pia Bornefeld-Ettmann, Dr rer nat, Clara Dittmann, Dr rer nat, Institute of Psychology, Goethe University Frankfurt am Main; Franziska Friedmann, MSc, Mascha Roth, MSc, and Anke Weidmann, Dr rer nat, Department of Psychology, Faculty of Life Sciences, Humboldt University. We thank our study therapists, as well as our supervisors, Dominik Ülsmann, Dr phil, Department of Psychiatry and Psychotherapy, Charité–Universitätsmedizin, Anne Dyer, Dr rer medic, ZPP, Central Institute of Mental Health Mannheim, Medical Faculty Mannheim, Heidelberg University, Ralf Winter, MSc, Institute of Psychiatric and Psychosomatic Psychotherapy, Central Institute of Mental Health Mannheim, Medical Faculty Mannheim, Heidelberg University, and Volkmar Höfling, Dr phil, Institute of Psychology, Goethe University Frankfurt am Main, Christian Stiglmayer, Dr phil, AWP Berlin. We thank Lydia Robnik, Institute of Psychiatric and Psychosomatic Psychotherapy, Central Institute of Mental Health Mannheim, Medical Faculty Mannheim, Heidelberg University, for grant management. We also thank Claudia Simonis, Dr rer nat, and Sabine Gack, Dr rer nat, Coordination Centre for Clinical Trials, Heidelberg University, for serving on our data safety and monitoring board. These individuals were compensated from the German Ministry of Education and Research for their contributions.

Author contributions

Drs Bohus and Kleindienst had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Drs Bohus and Kleindienst contributed equally to this work. Concept and design: Bohus, Kleindienst, Mueller-Engelmann, Lindauer, Steil, Priebe. Acquisition, analysis, or interpretation of data: All authors. Drafting of the manuscript: Vonderlin, Kleindienst, Bohus. Critical revision of the manuscript for important intellectual content: All authors. Statistical analysis: Vonderlin, Kleindienst. Obtained funding: Bohus, Steil, Schmahl. Supervision: Bohus, Mueller-Engelmann, Lindauer, Steil, Resick, Priebe.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data generated or analysed during this study are included in this article. Further enquiries can be directed to the corresponding author.
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