Introduction

Depression and anxiety disorders are among the most frequent mental disorders in the general population (Jacobi et al., 2014) as well as among psychotherapy outpatients (Gaebel, Kowitz, Fritze, & Zielasek, 2013; Velten et al., 2018). They carry a high burden of illness worldwide (GBD 2019 Mental Disorders Collaborators, 2022) and are associated with high illness costs (König, König, & Konnopka, 2019; Konnopka & König, 2020).
Lifetime traumatic events including childhood maltreatment (abuse and neglect) are often risk factors for the onset of a depression or anxiety disorder (Hovens, Giltay, Spinhoven, Hemert, & Penninx, 2015; Kühn et al., 2006; Mandelli, Petrelli, & Serretti, 2015; Walsh, McLaughlin, Hamilton, & Keyes, 2017) and are also predictors of depression and anxiety severity (Chu, Williams, Harris, Bryant, & Gatt, 2013; Hovens et al., 2010). Traumatic events can be classified as interpersonal or non-interpersonal and as single or repeated (Maercker & Augsburger, 2019). Interpersonal and repeated trauma types like childhood maltreatment and intimate partner violence have robustly been associated with more severe consequences such as higher posttraumatic stress disorder (PTSD), depression, and anxiety scores compared to non-interpersonal types such as traffic accidents and natural disasters (Bridges-Curry & Newton, 2021; Contractor, Brown, & Weiss, 2018).
Despite long-standing research on the effectiveness of CBT for depression and anxiety disorders (Carpenter et al., 2018; Hofmann, Asnaani, Vonk, Sawyer, & Fang, 2012; Tolin, 2010), about 51.5 to 59.0% of all patients do not respond to treatment (Cuijpers et al., 2021; Loerinc et al., 2015), calling for a better understanding of mechanisms involved in the treatment. One promising and cost-efficient way to identify potential CBT non-responders may lie in assessing and investigating psychological patient characteristics at the start of therapy (Kunas, Lautenbacher, Lueken, & Hilbert, 2021).
Childhood maltreatment predicts non-response and non-remission for a broad range of psychological and medical treatments for depression, including CBT (Nanni, Uher, & Danese, 2012; Nelson, Klumparendt, Doebler, & Ehring, 2017). Emotional, physical, and sexual abuse were related to lower response and higher post-treatment symptom severity for depressed patients treated with the Cognitive Behavioral Analysis System of Psychotherapy (CBASP) or Supportive Psychotherapy (Serbanescu et al., 2020). Emotional abuse in particular predicted less depression-free time in outpatients one year after psychotherapy (Bausch et al., 2020), while physical and sexual abuse were more frequently indicated by psychotherapy non-responders (Fischer et al., 2018). For patients with an anxiety disorder, the picture is less conclusive. In some studies, childhood maltreatment in general and more specifically emotional and physical abuse were linked to low psychotherapy response (Alden, Taylor, Laposa, & Mellings, 2006; Fischer et al., 2018). Other studies report no effect of childhood maltreatment (Santacana et al., 2016) or found an effect only on absolute levels of symptom severity, not on the amount of decrease (Bruce, Heimberg, Goldin, & Gross, 2013).
Effects of adulthood and non-interpersonal trauma on treatment success have, to our knowledge, scarcely been investigated. In one study, the overall effect of exposure-based CBT for panic disorder was similar for patients with and without trauma history (Trautmann et al., 2019). Only a subgroup of traumatized female patients, characterized by a specific genotype and comorbid depressive symptoms, achieved less change in symptom severity than the non-traumatized controls. Robust evidence on the effects of adulthood and non-interpersonal trauma on CBT response rates is missing.
Although negative effects of childhood maltreatment on treatment response have been demonstrated, questions remain concerning the relevance of these effects under different delivery conditions of CBT. Most studies, except for Fischer et al. (2018), investigated the effects of trauma only for CBT provided under controlled study conditions and used data from efficacy studies. These studies, while providing a maximum of experimental control and internal validity, often are not well transferable to therapies conducted under routine care conditions in terms of patient characteristics, number of therapy sessions, and especially the use of treatment manuals (Lincoln & Rief, 2004; Seligman, 1995; Shadish et al., 1997). Being aware of the trauma history of a patient gives the therapist the possibility to individually adapt the treatment by using specific interventions to address the trauma-related symptoms.
Victims of childhood maltreatment often present a more complex clinical picture at the start of CBT treatment compared with patients, who did not suffer childhood maltreatment (Fullana et al., 2019; Norman et al., 2012). They are more likely to have emotion regulation difficulties (Bridges-Curry & Newton, 2021) or engage in self-injuring behavior (Brown et al., 2018; Liu, Scopelliti, Pittman, & Zamora, 2018). These conditions may complicate the treatment of mental health problems and are risk factors for low treatment success (Kunas et al., 2021; Serbanescu et al., 2020; Taylor, Abramowitz, & McKay, 2012). Therapists might therefore offer skills training (Bohus & Wolf-Arehult, 2016; Cloitre, Koenen, Cohen, & Han, 2002; Linehan, 1993) to promote emotion regulation competencies in the early stages of therapy. Furthermore, childhood maltreatment is linked to an anxious or avoidant attachment style (Shahab et al., 2021; Widom, Czaja, Kozakowski, & Chauhan, 2018) and increased problems in intimate partner relationships in adulthood (Bender et al., 2022; Colman & Widom, 2004; Paradis & Boucher, 2010). Such interpersonal problems may affect the therapeutic relationship, which poses a key factor for successful therapy (Flückiger, Del Re, Wampold, & Horvath, 2018; Weck, Grikscheit, Jakob, Höfling, & Stangier, 2015), for example, by lowering relationship quality or raising difficulties in building a trustful working alliance (Alden et al., 2006). Consequently, interpersonal problems might mediate the link between childhood maltreatment and low therapy response. Supporting this notion, meta-analytic evidence points towards lower therapy success in patients with insecure attachment styles (Levy, Kivity, Johnson, & Gooch, 2018). Elements of schema therapy (Young, Klosko, & Weishaar, 2006), developed specifically for patients with challenging interpersonal behavior and a history of childhood maltreatment, might be applied to overcome problems in the therapeutic relationship and even modify dysfunctional attachment styles. Regarding persistent depressive disorder, deficits in social cognition, more specifically the phenomenon of preoperational thinking (McCullough, 2000, 2006), has been proposed as a mediator between childhood trauma and chronic, treatment-resistant depression (McCullough Jr., 2003; Struck, Gärtner, Kircher, & Brakemeier, 2021). Following McCullough (2006), maltreated and early-onset chronically depressed patients have difficulties in recognizing the effects they have on their interaction partners. They therefore cannot use the feedback obtained during interactions with their therapists to correct maladaptive assumptions and behaviors (McCullough, 2006). Supporting its relevance for treatment outcome, preoperational thinking is correlated with childhood maltreatment and a chronic course of depression (Klein et al., 2020) and can predict the course of depression over two years (Sondermann et al., 2020). Therapists might implement CBASP interventions like Disciplined Personal Involvement (McCullough, 2000) to reduce preoperational thinking and promote interpersonal learning. Regarding anxiety disorders, impaired extinction learning in trauma victims might contribute to low therapy success. Extinction of conditioned fear appears to be a key mechanism of exposure therapy for anxiety disorders (Craske et al., 2008; Craske, Treanor, Conway, Zbozinek, & Vervliet, 2014). It is the laboratory analog of exposure therapy (Barlow, 2002), during which a new safety memory trace is formed and can inhibit fear (Milad & Quirk, 2012). However, extinction learning may be impaired in patients with an anxiety disorder (Duits et al., 2015). Alterations in extinction learning observed in victims of childhood trauma aged 6-11 years might contribute to impaired extinction learning during adulthood (Marusak et al., 2021). There is also experimental evidence that supports impaired extinction learning following stress exposure in healthy adults (Klinke, Fiedler, Lange, & Andreatta, 2020) and in stress-exposed rodents (Knox et al., 2012; Wilber, Southwood, & Wellman, 2009; Yamamoto et al., 2008). Hence, trauma-exposed patients might experience slower or less robust extinction learning and, in parallel, profit less during exposure therapy (Maren & Holmes, 2016). They might, therefore, need a more extended treatment duration to compensate for slower learning.
These possibilities to individualize and intensify treatment in the naturalistic context might buffer adverse effects of trauma on treatment success observed in highly manualized therapy settings. Additionally, in the case of trauma-related avoidance behavior and hyperarousal, therapists might apply trauma-focused techniques (Neuner, 2012) and self-calming techniques (Reddemann, 2010) to treat these PTSD-like symptoms. To date, it remains open to what extent therapists under naturalistic treatment conditions apply trauma-specific interventions and unspecific intensification of therapy for traumatized patients. Furthermore, it is currently unknown if and how applying these measures affects treatment response.
Taken together, patients suffering from anxiety or depression, who additionally experienced trauma, seem to be at risk for non-response and non-remission in CBT treatment as these patients are more likely to present a complex clinical picture, have difficulties in the therapeutic relationship and possibly show reduced sensitivity to important CBT change mechanisms. Current evidence points towards more severe effects of interpersonal and childhood trauma compared to non-interpersonal and adulthood trauma. Still, the role of different trauma subtypes and the characteristics of the naturalistic therapy setting remain unclear. The present study aims to investigate treatment trajectories for depression and anxiety symptoms of patients with and without a trauma history in a naturalistic CBT context. It will distinguish between different trauma subtypes and test the role of the diagnostic group and trauma-specific therapy modifications as potential moderators of treatment success. We expect therapists to adapt treatment for patients with a trauma history by offering longer and intensified therapies and using trauma-specific interventions (Hypothesis 1). We also expect higher overall levels of symptom severity in the trauma group (Hypothesis 2a) and less decrease in symptom severity throughout therapy (Hypothesis 2b), especially for depressed patients (Hypothesis 2c). Furthermore, we expect the effect of trauma on symptom severity and decrease in symptom severity to be more pronounced in patients with a history of childhood trauma and interpersonal trauma in contrast to adulthood trauma and non-interpersonal trauma only (Hypothesis 3). Regarding the individualization of treatment in the naturalistic context, we expect to find more improvement in symptom severity for traumatized patients if trauma-specific therapy techniques were used (Hypothesis 4).