Psychological Treatment of Exhaustion Due to Persistent Non-Traumatic Stress: A Scoping Review

Background Exhaustion due to persistent non-traumatic stress (ENTS) is a significant health problem with substantial personal, social, and economic impact. While there are increasing studies of ENTS, there is no international agreement on how it should be diagnosed and treated. This scoping review aimed to map definitions, diagnoses, treatments, outcome measures, and outcomes in psychological treatment studies of ENTS. A further aim was to assess the quality of the treatments and map what change processes are described within ENTS interventions. Methods A PRISMA-guided scoping review of psychological treatment studies delivered in a clinical setting for ENTS was conducted using the databases of PubMed, PsycINFO, and CINAHL. Results Of the 60 studies included, the majority (87%) stemmed from Europe. The most recurrent term for ENTS was burnout, and the diagnosis most often utilized was exhaustion disorder. Several treatments were reported, the most frequent being cognitive behavioral therapy (CBT) (68%). Statistically significant outcomes relevant to ENTS were reported in 65% (n = 39) of the studies, with effect sizes between 0.13 and 1.80. In addition, 28% of the treatments were rated as high quality. The most frequent change processes described were dysfunctional sleep, avoidance, behavioral activation, irrational thoughts and beliefs, worry, perceived competence/positive management, psychological flexibility, and recuperation. Conclusions While several treatments based on CBT show promising results for ENTS, there do not seem to be any uniformly established methods, theoretical models, or change processes. Instead of adopting a monocausal, syndromal, and potentially bio-reductionist perspective on ENTS, a process-based approach to treatment is encouraged. Supplementary Information The online version contains supplementary material available at 10.1007/s12529-023-10185-y.


Introduction
Persistent non-traumatic stress can have detrimental health effects and can result in symptoms of exhaustion, reduced performance, and cognitive impairments [1][2][3][4].Today, stress-related disorders are the leading cause of work absenteeism in the Organization for Economic Co-operation and Development (OECD), and the indirect costs of work-related stress have been estimated to be €20 billion annually in the European Union [5][6][7][8].A particular stress-related disorder called exhaustion due to persistent non-traumatic stress (ENTS) is an increasing subject of clinical research [9][10][11][12][13][14].The cardinal symptoms of ENTS include substantial debilitating levels of exhaustion coupled with cognitive impairments, but not necessarily a depressed mood [15].There is, however, no international agreement on if or how ENTS should be diagnosed and how to best treat it [16].
ENTS is not something new.In 1869, George Miller Beard described the diagnosis of neurasthenia, a condition -well known to clinical practitioners of that time -characterized by persistent exhaustion due to the fast pace and demands of the "modern life," as Beard himself put it [17].In the late nineteenth century, neurasthenia became one of the most common diagnoses used throughout the western world.The German psychiatrist Emil Kraepelin, known for his work with the classification of mental disorders, described neurasthenia as "the disease of our time" and distinguished it from other mental illnesses as an "acquired syndrome" [18].However, with the introduction of psychoanalysis, favoring internal psychological explanations for mental disorders, followed by the world wars, the scientific interest in neurasthenia faded [19].With the introduction of the non-etiological Diagnostic and Statistical Manual system (DSM) in psychiatry in the second half of the twentieth century, neurasthenia appears to have been subsumed within other diagnoses [20].
For the past 40 years, the interest in ENTS has been reawakened through the concept of burnout, a construct used in organizational psychology to describe how employees gradually succumb to exhaustion, cynicism, and professional inefficiency due to organizational factors [21].Burnout is not classified as a disorder in the International Classification of Mental and Behavioral Disorders (ICD-10), nor in the Diagnostic and Statistical Manual, fifth edition (DSM-5) [22,23].Instead, clinical burnout is sometimes used to describe the end stage of a severe burnout process that requires clinical attention [24,25].In Sweden, the diagnosis of exhaustion disorder has been accepted into the Swedish ICD-10, and in other countries, terms such as work-related neurasthenia, "work-related depression," "adjustment disorder," and "somatization syndrome" are used interchangeably to describe clinical burnout/ENTS [15].There is an ongoing debate as to whether ENTS should be considered a disorder on its own or whether it should be a part of depression, with diverging evidence currently supporting both positions [26][27][28][29][30][31][32].The nosological confusion surrounding ENTS is matched with equal confusion around treatment, perhaps not surprisingly.No evidence-based treatment has been identified for ENTS, and it appears that various treatments with varying theoretical frameworks, components, and methods are utilized in regular care [16].
In recent years, there has been a call for psychological treatment research to increase its focus on treatment models (a) built upon testable theories, (b) targeting specific evidence-based processes of change, and (c) tailored to individual people's needs [33].Change processes are the specific variables through which a treatment method exerts its influence over a targeted dependent variable [34].It is argued that these processes should be theory-based, manipulable, dynamic, and multilevel [35].A focus on evidence-based change processes can have advantages compared to a focus on treatment types.Perhaps ENTS is not best understood as a discrete disease needing a specific treatment type.Maybe it is a condition that emerges from a network of pathological interactions of behavioral, cognitive, emotional, physiological, and social elements -a network that can be altered by targeting explicit processes of change, in specific situations, for particular people [35].
There is a clear need to assess existing clinical treatments for ENTS to help focus future theory development and increase international consensus.A scoping review is an excellent way to map a field of study particularly one still in its youth, where more detailed questions are not yet possible [36].Therefore, the purpose of this scoping review was to map the different definitions, diagnoses, treatments, outcome measures, and outcomes achieved in clinical treatment studies of ENTS.In addition, given the increased focus on testable theories and processes of change within contemporary psychological treatment research, the current review also aimed to assess the quality of the treatments utilized for ENTS and explore what processes of change are described within these interventions.

Method
This scoping review was conducted following the guidelines from the Joanna Briggs Institute, and the reporting follows the PRISMA-ScR guidelines [37,38].An unpublished protocol stating the scoping review process was developed a priori.Furthermore, a PRISMA-ScR checklist is supplied within the supplementary material.

Information Sources and Database Search
Three databases, PubMed, PsycINFO, and CINAHL, were selected for the current scoping review.The research team developed search terms aimed at providing both scope and precision for each of the specific concepts included in this review: (a) ENTS and (b) psychological treatments or multimodal interventions with a substantial psychological component.First, a preliminary search was conducted.The team then added search terms to the list, including new search terms found in the search results and adjustments to accommodate each database.
The final search strategies for each database were discussed with two research librarians before commencing the search on January 7, 2021.The database search was repeated on May 10, 2022, to include recently published papers.In addition, the search was supplemented by reviewing the reference lists of the included articles.

Eligibility Criteria
A study was eligible for inclusion if it (a) appeared as a full-text primary research report available in English; (b) included adult (≥ 18 years) participants; (c) included participants with conditions associated with exhaustion, including burnout, work-related depression, adjustment disorder, exhaustion disorder, due to some form of explicitly defined long term non-traumatic stressor; (d) involved treatment delivered in a clinical setting; (e) used a quantitative treatment design, including a clinical outcome; and (f) described or examined the impact of psychological treatment(s) or multimodal interventions with a substantial psychological component.Treatment was deemed psychological if it was based on psychotherapeutic or behavioral change principles and included related methods.
A study was excluded if it (a) targeted stress in general (rather than conditions associated with the presence of longterm stressors as described in the inclusion criteria), (b) if the severity of the condition and/or need for intervention by professionals in a clinical setting was not assessed or reported, (c) described treatment that was delivered in a nonclinical setting (e.g., workplace interventions), (d) solely used a qualitative study design, or (e) was a study protocol of a future study.

Screening
Before beginning the screening of abstracts, the complete search of each database was imported to Endnote, where duplicates were removed.Next, a pilot screening was carried out to ensure inter-rater reliability.Two of the reviewers independently applied the eligibility criteria to the random sample of 10 abstracts and compared their results (AÅ and JCvdL in the first search, JCvdL, and FJ in the updated search).There was an > 90% agreement in the results.The screening was then carried out independently, using the webbased tool Rayyan (https:// rayyan.qcri.org/).If there was any uncertainty about whether a paper was eligible, the paper was included for a closer assessment in the selection phase.

Selection
Before commencing the selection process, another pilot selection of 10 articles was carried out to ensure inter-rater reliability with > 90% agreement (AÅ and JCvdL in the first search, JCvdL, and FJ in the updated search).The remaining full-text articles were independently read in full by three reviewers and assessed for eligibility (AÅ and JCvdL in the first search, JCvdL, and FJ in the updated search).Discrepancies were resolved by the fourth and fifth reviewers (LM, MB).

Data Extraction Process
In the extraction phase, three reviewers extracted information from all included papers into tables (JCvdL, AÅ, FJ).The following information was extracted: study location, design, number of participants, age, gender, control condition, setting, population, inclusion and exclusion criteria, terms used for ENTS, diagnostic label(s) used, type of intervention(s), treatment model used, suggested processes of change, profession delivering the intervention(s), the scope of the intervention(s), the format of intervention(s), use of follow-up measurement, outcome measures, outcome variables (primary and secondary), significant outcomes, and effect sizes.The average mean and SD were pooled in cases where age, means, and standard deviations (SD) were presented separately for different treatment conditions [39].

Quality Assessment
Based on the recommendations of Hayes et al. [40], a quality assessment tool was developed.A psychological treatment is of high quality if: The intervention is rooted in a theoretical model that serves as an organizing framework for predicting psychological change with high clinical utility.The framework includes specific, quantifiable components and defines processes and outcomes (dependent and independent variables).These stipulated processes of change are based on scientifically well-established psychological principles.Based on this definition, four criteria were extrapolated, yielding a treatment quality score ranging from zero to four: • Is there an explicit theoretical framework described as the basis for treatment?(Yes = 1 point, No = 0 point) • Is the theoretical framework based on scientifically wellestablished psychological principles?(Yes = 1 point, No = 0 point) • Are processes of change described within the theoretical framework?(Yes = 1 point, No = 0 point) • Are specific methods or components targeting the proposed processes of change described?(Yes = 1 point, No = 0 point) A pilot treatment quality assessment was implemented once more to ensure inter-rater reliability.First, one article was rated together by two reviewers (JCvdL and AÅ), followed by a pilot rating of five papers with > 90% agreement (4 ratings per paper, making it a total of 20 ratings).Then, all remaining papers were quality assessed independently, and discrepancies were resolved with the rest of the reviewers (LM, MB, FJ).

Selection of Sources of Evidence
The electronic search identified 8701 articles, and 6215 of these remained after duplicates were removed.Most of the titles and abstracts screened did not address clinical psychological treatments or ENTS.In total, 163 full-text articles remained after screening.Following the selection phase, 72 articles were included.However, some included papers were secondary analyses or long-term follow-ups of the same population based on the same trial.These papers were included in the data extraction process, but their information was combined in the results into one paper, using the primary report as the chief reference.This yielded a total of 60 studies, and each row in the tables is referred to as "one study" from this point onward.See Fig. 1 for a flow diagram of the screening process and reasons for exclusion.

Study Characteristics
The included 60 studies were published between 1986 and 2022 (see Table 1).The studies primarily stem from Europe (52 studies), with the most common locations being Sweden (20 studies), followed by the Netherlands (12 studies), and England, Denmark, Finland, and Nigeria (5 studies each).In addition, three studies came from North America.The specific location of each study is described within the supplementary material.Study designs included 28 RCTs, nine single-group designs, six quasi-experimental designs, five pilot studies (of which three were with no control, one with a healthy control, and one with a no treatment control), and five open clinical trials.Furthermore, three included studies were case studies, two matched control designs, one retrospective (cohort) study, and one used a crossover design.While reporting outcomes and contents of treatment, 10% of the included studies (n = 6) did not specifically have the primary focus to evaluate a clinical intervention but instead other aims, such as investigating biomarkers, mediators, or subgroup trajectories during treatment [46,101,102,[110][111][112].
The average number of study participants was 89, ranging from 1 to 390, with a median of 78.The average age for participants was 42.4 (9.0), and most were women, averaging 70%.Seven included studies did not report mean age, and six did not report sex.One of the studies [66] only included male participants, while three only included women [50,64,105].Detailed accounts of age and gender are provided in the supplementary material.

Terms and Diagnoses Used for ENTS
The most common term used for ENTS was burnout (n = 20).In total, seven different terms were used (see Fig. 2).No diagnosis was used for ENTS in thirty-one of the studies.The most common diagnosis used was exhaustion disorder (n = 9).Seven different diagnoses were used in the included studies (see Fig. 2).

Treatments Used for ENTS
Different forms of cognitive behavior therapies (CBT) were examined in 64% of the studies (n = 38).Of these, six studies specifically investigated rational emotive behavior therapy (REBT), five investigated CBT rehabilitation, three investigated a combination of CBT and acceptance and commitment therapy (ACT), two studies specifically studied ACT, and two used mindfulness interventions.Eclectic treatment protocols described best as generic stress-coping treatments were utilized in 10% of the included studies (n = 6).Furthermore, 8% of the included studies investigated psychodynamic interventions (PDT; n = 5), 7% investigated treatments influenced by eastern philosophy (yoga, Qigong, mindfulness; n = 4), and 5% occupational therapy (n = 3).Finally, 17% of the included studies (n = 10) investigated treatments deemed as "alternative," including five focusing on nature-based rehabilitation, one on guided imagery and music, one on experiential therapy, one on psychodrama, one on flotation tank in addition to unspecified therapy, and one on hypnotherapy in addition to CBT.
Group treatment was included in 52% of the treatments (n = 31), and 39% of these (n = 12) also included individual treatment.Of the treatments, 45% (n = 27) were individual alone.Treatment was delivered face-to-face in 88% of the studies (n = 53), 10% via the Internet (n = 6) 2% (n = 1) via phone.The average treatment length was 14.7 weeks (SD = 9.4), ranging from 1 week to 1 year.Treatment length was not reported in 12% (n = 7) of the studies.In 20% (n = 12) of the studies, no description of treatment delivery was provided.At least one psychologist or psychotherapist was involved in delivering the treatments in 50% (n = 30) of the studies.In 30% (n = 18) of the studies, treatment was delivered by professionals other than a psychologist/psychotherapist.Detailed accounts of treatment delivery, format, and length are provided in the supplementary material.

Quality of Treatment and Processes of Change
The largest portion of the included studies, 37% (n = 22), received a score of two in our quality-of-treatment rating, describing a treatment framework based on well-established psychological principles (see Table 1).Of the included studies, 28% (n = 17) received a maximum score of 4, indicating a high-quality treatment including a treatment framework, established psychological principles, definable change processes, and components targeting these processes.
Of the 60 studies included, 48% (n = 29) described one or more change processes.However, seven of these described a treatment framework not based on well-established psychological principles, reducing the proportion to 37% (n = 22) describing change processes in conjunction with wellestablished psychological principles.In total, there were 16 suggested processes of change from the treatment framework with

Treatment Outcomes and Results
Detailed accounts of outcome measures and outcomes are provided in the supplementary material.

Measures and Use of Follow-Up
The most frequent outcome measure was sick leave/absenteeism/return to work (n = 16).The most employed measures of ENTS were the Shirom-Melamed Burnout Questionnaire (SMBQ; n = 12), the Maslach Burnout Inventory (MBI; n = 8), and the Oldenburg Burnout Inventory (OLBI-S; n = 6).For anxiety and depression, the most frequent measures used were the Beck Depression Inventory (BDI; n = 12), and the Hospital Anxiety and Depression Scale (HADS; n = 6).Short-term stress was measured most often with the Perceived Stress Scale (PSS; n = 10).Follow-up was assessed in 68% (n = 41) of the studies, and primary outcomes were explicitly defined in 27% (n = 16) of the studies.

Statistical Significance and Effect Sizes
None of the three case studies reported testing of statistical significance or effect sizes.Although, in two of the case studies [41,43], the participants improved from pre-to posttreatment.In the third case study [42], 55-73% of the participants showed reliable clinical improvement at 6 months follow-up, depending on the outcome instrument.
Of the studies including between-group comparisons and a passive control condition, 75% (n = 15) reported significant outcomes (relevant for the research question and/or regarding ENTS) and 75% (n = 15) reported effect sizes.Effect sizes were reported in terms of Cohen's d (range between 0.21 and 1.37), Hedge's g (range between 1.4 and 1.8), etasquared (range between 0.15 and 0.51), partial eta-squared (range between 0.44 and 1.0), and an unspecified effect size measure (range between 0.75 and 1.22).Of the controlled studies with at least one active control, 63% (n = 10) reported significant outcomes (relevant to the research question and/ or regarding ENTS), and 44% (n = 7) reported effect sizes.Effect sizes were reported in terms of Cohen's d (range between 0.26 and 1.11), Hedge's g (range between 0.85 and 1.49), eta-squared (used once, η 2 = 0.13), and partial etasquared (used once, η 2 p = 0.21).
Of the studies including only within-group comparisons, 78% (n = 14) reported significant outcomes and 22% (n = 4) reported effect sizes.Effect sizes describing within-group effects were reported in terms of Cohen's d (range between 0.3 and 1.8), Pearson's r (range between 0.53 and 0.65), an unspecified effect size (range between 0.30 and 1.29), and percentage difference in proportions below/above an SMBQ cutoff of 4.4 (range between 23.5 and 40%).

High-Quality Studies
Of the 17 studies with a total score of 4 points in the treatment quality rating, 59% (n = 10) reported significant outcomes.Regarding treatment type, CBT was used in 30% (n = 3), REBT in 20% (n = 2), CBT/ACT in 10% (n = 1), mindfulness in 20% (n = 2), CBT-based rehabilitation in 10% (n = 1), and CBT and/or a return-to-work intervention in 10% (n = 1) of the studies.Of the studies with both a score of 4 points in the quality rating and significant outcomes, 100% (n = 10) were CBT-or mindfulness-based.

Secondary Analysis and Findings
Secondary analyses were included (within the study or as a complementary paper) in 57% (n = 34) of the studies.Secondary findings and results beyond treatment outcomes are described in more detail within the supplementary table.Of all secondary findings, only one was replicated across two studies, showing that the effect of Internet-CBT on symptoms of stress and exhaustion was mediated by insomnia severity [68,80].

Discussion
This scoping review aimed to examine and map the different definitions, diagnoses, treatments, outcome measures, and outcomes in clinical psychological treatment studies of ENTS.A further aim was to assess the quality of treatments and examine what processes of change are described within interventions for ENTS.Of the 60 studies included, 53 were based in Europe, with the most common locations being Sweden and the Netherlands.The term most associated with ENTS was burnout, and the most frequent diagnosis was exhaustion disorder.A wide array of treatments was applied, most commonly variations of CBT (68%).Psychologists or psychotherapists delivered treatment in only half of the studies, yielding some uncertainty about treatment competency and fidelity.Statistically significant results for outcomes relevant to ENTS were reported in 65% (n = 39) of the studies, with effect sizes ranging between 0.13 and 1.80.The most used outcome measures were sick leave/absenteeism, SMBQ (measuring burnout), and BDI (measuring depression).
Most of the included studies (73%) described a treatment framework established on well-defined psychological principles.Still, only 28% of the treatments were rated as high quality, including an established treatment framework with specific processes of change and methods targeting those processes.The most frequent change processes described were dysfunctional sleep, avoidance, behavioral activation, irrational thoughts and beliefs, worry, perceived competence/positive management, psychological flexibility, and recuperation.In summary, several different treatments, especially forms of CBT, show some promising results, but currently, there do not seem to be any uniformly established treatments, consistently adopted theoretical models or precisely specified processes of change for ENTS.

Clinical Utility of ENTS Diagnostics Across Varying Geographical Discourses
Besides operating as a taxonomy to coordinate clinical practice and academic research, diagnoses of mental disorders should, according to the DSM-5, have clinical utility.More specifically, diagnoses should "help clinicians to determine prognosis, treatment plans, and potential treatment outcomes for their patients" [23].In the current review, diagnoses were typically not used in the included studies.When used, a wide array of stress-and depression-related diagnoses is utilized (most often in the F43-category or F32-category within the ICD).Even when diagnoses are used, however, they appear to play little role in guiding treatment.Instead, it appears to be the other way around: Researchers are interested in a specific treatment for ENTS and use the available diagnoses to describe the population.Thus, the clinical utility of the diagnoses currently used for ENTS remains to be determined.
Several of the studies from Sweden use the diagnosis of exhaustion disorder, which is only applied in Sweden.Of course, diagnoses facilitate access to health care and social insurance.Perhaps not surprisingly, more than half of the included studies in the current review stem from Sweden (n = 20) and the Netherlands (n = 12), countries with extensive public healthcare and social insurance systems.The fear of increasing healthcare and social insurance costs and medicalizing "regular" work stress by accepting ENTS as a medical diagnosis is evident in the national writings discussing the matter [10,113].Conversely, the lack of studies originating from the USA is striking, given that the concept of burnout, to a large extent, stems from research in the USA and is widely accepted within organizational research.Perhaps the lack of clinical treatment studies from the USA reflects the absence of clinical diagnoses in the specific healthcare context of the USA.
Skepticism around the clinical utility of syndromal diagnoses is not unique to ENTS.Mental health professionals and researchers have long debated the most effective ways to define and classify mental disorders [114].Compared to many other medical diagnoses based on biological underpinnings and signs, psychiatric diagnoses primarily rely on self-reported symptoms.Conveniently, syndromal diagnoses are clinical judgments that lack independent validation, and so what is or is not a disease is, to a large extent, socially negotiated through scientific discussion and clinical practice [115], which currently centers around the ICD and DSM.
The DSM and ICD systems assume that diagnoses reflect underlying disease processes, but there is growing agreement that the current diagnostic categories for mental disorders lack clinical utility [116].In fact, the DSM-5 workgroup themselves have suggested that the reification of DSM-IV entities as equivalent to diseases can obscure rather than elucidate research findings [117].So, while the validity and reliability of ENTS are faced with challenges, these challenges are shared across several mental disorders within the DSM and ICD systems.Instead of viewing ENTS as a static diagnostic category, conceptualizing it as a dynamic network of multilevel biopsychosocial processes of change may offer a promising way forward for improving international consensus on clinical interventions and theories for ENTS.Of course, this discussion is not to equate ENTS with a mental disorder but simply to note the similar challenges faced in these separate health contexts.

Quality of Treatment and Treatment Theory for ENTS
In our quality ratings, the largest proportion of the included studies, 37% (n = 22), received a score of two describing a treatment framework based on well-established psychological principles.Today CBT is a broad family of methods with many alternate or even subtly conflicting theories and underlying assumptions.Therefore, only describing treatment as CBT leaves considerable latitude regarding the treatment's theory, focus, and contents.
While 37% (n = 22) of the included papers described some form of the change process in conjunction with wellestablished psychological principles, few explicitly define how these specific change processes relate to the origin and maintenance of ENTS.The lack of theory-driven evidencebased treatments for stress-related conditions such as ENTS, compared to anxiety and mood disorders, has previously been highlighted [79].One possible explanation could be the monocausal latent disease model inherent in a syndromal approach, favoring biologic reductionism over a complex multilevel view [118].From a biomechanical view, persistent stress symptoms are regarded as the result of a physiological resource-demand imbalance rather than a consequence of interacting physiological, behavioral, cognitive, emotional, and social elements [119].Such biomechanical perspectives risk fostering generic methods focusing on problem-solving, relaxation, and coping rather than encouraging the development of treatment theory about what specific processes initiate and maintain ENTS.Consequently, future clinical treatment models would probably benefit from focusing more on such processes to promote the development of theory-driven, evidence-based treatments for ENTS.This includes exploring what progressive step-by-step changes in physiological, behavioral, cognitive, emotional, and social domains result in severe debilitating exhaustion symptoms in the context of persistent non-traumatic stress.

Processes of Change -Toward a New Treatment Perspective on ENTS
In recent years, a group of prominent researchers in clinical psychology have set out to change the agenda for modern clinical interventional research: away from syndrome-based diagnoses and syndrome-specific protocol-based interventions and toward a process-based approach to treatment [33].Instead of a monocausal latent disease model for understanding illnesses, a network approach is recommended, conceptualizing mental illness from a multicausal network of interacting symptoms and associated processes, where specific syndromes are the result of dynamically self-reinforcing clusters [120,121].Process-based therapy adopts an idiographic perspective where treatment models should have explicit philosophical assumptions, be theoretically coherent and enable clinicians to select components to target established, evidence-based, and modifiable change processes tailored to specific individuals [122].
In a recent literature review on the mediation of psychosocial interventions for mental health, Hayes et al. [123] identified 66 replicated measures of unique mediators, accounting for 281 specific findings across 204 studies [123].Of the most frequent processes of change identified in the current review, behavioral activation, worry, and psychological flexibility are all represented.While not described in the review of Hayes et al. [123], avoidance and perceived competence are incorporated within several overlapping constructs, such as self-efficacy, nonreactivity to inner experience, and perceived control in the present.Furthermore, approaching behaviors in line with values, rather than being governed by negatively reinforced avoidance, constitute a central part of psychological flexibility [124].
Given the complexity and potential heterogeneity of ENTS, together with the current lack of consensus in international nomenclatural, it seems advisable to adopt an approach to treatment delivery that can customize itself around individual participants' needs rather than assuming one set protocol will best fit everyone.Furthermore, a process-based approach could shift the academic focus of ENTS over time.This focus could shift away from whether ENTS exists "by its own right" as a latent disease within the already debated diagnostic systems, where low specificity and high comorbidity are the norm rather than the rule [116].Instead, the focus could shift toward an understanding of what change processes generate and maintain ENTS for particular people in specific contexts.Such an approach could potentially enable research that results in better psychological interventions with higher clinical utility and, consequently, better treatment outcomes for individuals with ENTS.One first step toward such an approach would be for future research to focus on optimizing effects on established change processes currently utilized within ENTS treatment.

Limitations
One limitation of the current review is it is a scoping review and not a systematic review of efficacy -this remains to be done.Since the specific aim of this review was mapping the literature, the large number of trials is summarized into frequency counts or percentages at the risk of concealing individual yet essential clinical findings.Many of the included studies contained potentially important secondary findings, such as trajectories for patients going through long-term rehabilitation for burnout [110] or economic outcomes.For example, it appears that using ACT, work-directed intervention (WDI), and a combination of both reduced healthcare costs, whereas WDI alone reduced welfare costs [59].Other interesting results relate to differences in lower cortisol levels at awakening [101,102] or reductions in the arousal from sleep being predictive of decreased exhaustion symptoms during treatment [93].While described within the supplementary table, these were outside the scope of the current review.A different approach and review methods focusing beyond simply "scoping" could reveal nuances and findings not made available with the current descriptive approach.
One significant limitation of the current review is that its findings are primarily based on European studies.This geographic discrepancy may be due to the focus of the intervention on clinical treatments for stress-related disorders, which are seldom covered by public healthcare and social insurance systems.Additionally, differences in cultural conceptualizations of ENTS and what is considered a condition warranting professional healthcare interventions could contribute to these disparities.To enhance the understanding of the definitions, treatments, and theories surrounding ENTS, it may be beneficial to expand the scope beyond clinical interventions published in English scientific journals.This could involve exploring non-Western sources and incorporating perspectives from diverse cultural and linguistic backgrounds.Such an approach could provide valuable insights into the cross-cultural variations in the manifestation and treatment of ENTS.
In the clinical research literature, the terms "mechanisms of change," "mediators," and "processes of change" are often used interchangeably with different underlying definitions and assumptions.This is understandable, given the relative novelty of these concepts in the field.In this review, an inclusive approach was used to capture all potential change processes available and to avoid judging previous research efforts based on the new standards of process-based therapy.A stricter definition of change processes in the current review focusing on the quality of the description rather than frequency across studies may have led to more limited but more informative results.Going forward, a coherent definition of change processes is encouraged in developing ENTS treatments since this would make translating findings across different treatments and studies easier.
Lastly, while our quality assessment is based on clinical recommendations, it is not an established rating system and has not been utilized elsewhere.What is to be considered a high-quality psychological treatment is a question not easily answered and will vary across different perspectives within clinical psychology.The current scoping review has strived for transparency regarding its assumptions about what a psychological treatment of high quality is, but different assumptions would most certainly have yielded different quality assessment results.

Conclusion
Several psychological treatments for ENTS, primarily forms of CBT, show promising results.Currently, however, there seem to be no well-established treatments, theoretical models, or processes of change established for ENTS.Instead of utilizing a monocausal, syndromal, and potentially bioreductionist perspective on ENTS, future clinical research efforts would probably benefit from embracing a processbased approach to treatment, as presently reflected in the wider field of clinical psychology.An appropriate place to start may be those already established change processes identified in the current review: avoidance, psychological flexibility, self-efficacy, worry, and irrational thoughts and beliefs.Perhaps focusing on multilevel biopsychosocial change processes could help bridge the gap between the current lack of theory-driven, evidence-based treatments for ENTS compared to anxiety and mood disorders.

Fig. 1
Fig. 1 Flow chart illustrating the screening and selection process of this scoping review

Box 1 .x, n = 1 x
well-established psychological principles (see Box 1).Based on frequency and range across different treatments and research groups, relevant processes of change of ENTS, as suggested by published clinical trials for ENTS, are dysfunctional sleep, avoidance, behavioral activation, irrational thoughts and beliefs, perceived competence/positive management, psychological flexibility, and recuperation.Processes of change, ranked in frequency of appearance x Dysfunctional sleep, n = 5 (Four different treatments and research groups) x Avoidance, n = 5 (Four different treatments and research groups) x Behavioral activation, n = 4 (Three different treatments and research groups) x Irrational thought and beliefs, n = 4 (Two different treatments and research groups) x Perceived competence/positive management, n = 3 (Three different treatments and research groups) x Worry, n = 2 Two different treatments and research groups) x Psychological flexibility, n = 2 (Two different treatments and research groups) x Recuperation, n = 2 (One treatment and research group) BalanceCognitive deficits, n = 1 x Increased awareness of internal states, n = 1 x Internal conflicts in conjunction with relational conflict constellations, n = 1 x Mindfulness, n = 1 x Negative appraisals of threat, n = 1 x Over-engagement and learning to let go, n = 1 x Self-compassion, n = 1 x Self-esteem, n = 1 x Social support, n = 1

Fig. 2
Fig. 2 Distribution of terms and diagnoses used for exhaustion due to persistent non-traumatic stress (ENTS) in the included studies (N = 60)

Table 1
Design, treatment, suggested processes of change, and quality of treatment ratings for all of the included studies (N = 60) constellations Buxton et al., 2020 [47] RCT Mindfulness-based day hospital treatment (+ CBT elements) Over-engagement, letting go and increasing awareness of states, needs and stress levels Dalgaard et al., 2017 [48] Prospective RCT W ork-focused CBT N S de Vente et al., 2008 [49] RCT CBT-based stress management training Negative appraisals of threat

Table 1 (
continued) NS not specified, RCT randomized controlled trial.Treatment: ACT acceptance and commitment therapy, CBT cognitive behavioral therapy, MBCT mindfulness-based cognitive therapy, MMI multimodal intervention1 3