A scoping review of ICD-11 adjustment disorder research

ABSTRACT Background: Adjustment disorder (AjD) is one of the most used mental disorder diagnoses among mental health professionals. Important revisions of the AjD definition in the 11th edition of the International Classification of Diseases (ICD-11) are proposed. AjD is included in a chapter of disorders specifically associated with stress in ICD-11. Objective: This paper aims to review recent developments in ICD-11 AjD research, and to discuss the available ICD-11 AjD diagnosis validation studies, AjD measures, treatment studies, and outline the future perspectives for AjD research and clinical practice. Methods: In total, 10 empirical studies of AjD ICD-11 were identified and included in this review. We searched for studies in Embase, PubMed, PsycINFO, Scopus, PILOTS, SocINDEX, and via additional search by contacting authors of published empirical studies and reference screening. Results: Review of the studies revealed a lack of validation studies of the ICD-11 AjD symptom structure. AjD validation study findings are ambiguous, and there is still little support for the proposed two symptom structure of AjD for the ICD-11. A self-report AjD measure ‘Adjustment Disorder New Module’ (ADNM) based on the ICD-11 definition has been developed and used in all 10 reviewed studies. Two self-help interventions have been developed for the ICD-11 AjD, and findings from these studies indicate that self-help low-intensity cognitive-behavioural interventions, delivered via bibliography or internet-based, might be effective treatment of AjD. Conclusions: The AjD definition in ICD-11 with a description of a new symptom profile facilitates AjD measurement and AjD-focused treatment developments. More studies and insights from clinical practice are needed to move the field of AjD research and practice forward.


对ICD-11适应障碍研究的审视综述
Adjustment disorder (AjD) is one of the most used mental disorder diagnoses among psychologists and psychiatrists according to worldwide surveys of mental health professionals (Evans et al., 2013;Reed, Mendonça Correia, Esparza, Saxena, & Maj, 2011). AjD is a mental disorder with serious implications; in particular, it is highly associated with suicidality (Casey, Jabbar, O'Leary, & Doherty, 2015). A recent longitudinal study revealed that AjD is a common condition after traumatic injuries (O'Donnell et al., 2016). Still, AjD remains largely neglected in research, in contrast to other stress-related disorders such as posttraumatic stress disorder (PTSD) or complex PTSD (Brewin et al., 2017).
The AjD definition has passed revisions in International Classification of Diseases (ICD). The first attempt to define AjD in ICD was the inclusion of 'transient situational disturbances' diagnosis in the eighth edition of ICD in 1965, and 'adjustment reaction' in the ninth edition of ICD in 1975. Under the name of 'adjustment disorder' this diagnosis was included in the 10th edition of the ICD, and was defined as a subjective distress or emotional disturbance following a significant life change or stressful life event (WHO, 1992). The ICD-10 AjD definition described potential stressors, and included symptoms of depressed mood, anxiety, or worry in addition to functional impairment following a stressor. Important revisions of the AjD definition are in the 11th edition of the ICD (ICD-11). AjD is included in the new chapter of 'Disorders Specifically Associated with Stress' in ICD-11, along with other stress-related disorders, such as PTSD, complex PTSD, and prolonged grief disorder (PGD) (Maercker et al., 2013).
The main changes of AjD description in ICD-11 (ICD-11 AjD) in contrast to the ICD-10 definition of AjD is the clear definition of symptoms (Maercker et al., 2013). AjD is defined in ICD-11 as a maladaptive reaction, which usually emerges within one month of a significant life-stressor, such as illness, family or partnership problems, job-related issues, or financial difficulties. Two symptoms constitute AjD: (1) preoccupation with a stressor or its consequences; (2) failure to adapt (Maercker et al., 2013). Preoccupation with a stressor is associated with recurring distressing thoughts about the stressor, constant worry about the stressor, or rumination about the stressor. Failure to adapt describes a generalized stress-response (e.g. sleep disturbances or concentration problems) that results in significant impairment in social, interpersonal, occupational, educational, or other significant areas of functioning (Maercker et al., 2013). A recent update of the AjD definition in ICD-11 included exclusion criteria (WHO, 2017). AjD can be diagnosed only if symptoms do not reach sufficient specificity or severity of other mental disorder, similar to the DSM-5 AjD definition (American Psychiatric Association, 2013). AjD usually resolves itself within six months, unless the duration of the stressor is longer (Maercker et al., 2013).
This paper aims to review recent developments in the ICD-11 AjD research, and to provide up-to-date knowledge about the ICD-11 AjD for researchers and clinicians. We discuss ICD-11 AjD validation studies, AjD measures, treatment studies of AjD, and future perspectives for AjD research and clinical practice in our paper.

Method
We followed guidelines for scoping reviews in extracting and reporting data (Levac, Colquhoun, & O'Brien, 2010). The main question for this study was to identify and review the empirical studies of the ICD-11 AjD, including ICD-11 AjD symptom structure validation studies, ICD-11 AjD measures, and ICD-11 AjD treatments to evaluate the available evidence for the ICD-11 AjD symptom structure, measures, risk factors, and treatments. Our inclusion criteria for this review were: (1) AjD symptoms measured using ICD-11 diagnostic criteria, (2) the empirical data reported, and (3) the study was peerreviewed and published.
We searched for published ICD-11 AjD studies using the keywords 'adjustment disorder' and 'ICD-11ʹ in abstracts and titles of articles indexed in Embase, PubMed, PILOTS, PsycINFO, Scopus, and SocINDEX databases in August 2017. The search in the databases revealed 25 articles. Two reviewers independently screened the abstracts of the extracted articles. After screening of titles and abstracts, we identified six published ICD-11 AjD empirical studies meeting our inclusion criteria. In total, 19 papers from the database search were excluded from further analysis because they were theoretical, study protocol papers, or other articles without reported empirical data. After the database search we screened the reference lists, and contacted authors of the extracted studies to enquire about other AjD published papers or articles in press. We identified four more articles in addition to the six studies identified through database search, which met inclusion criteria for this review.
In total, 10 empirical studies were included in the full-text analysis. Data from the 10 full-text articles were extracted by the two reviewers. Sample descriptions, methods, and main findings of the 10 published AjD ICD-11 studies included in this review are presented in Table 1. All participants in the reviewed studies were adults, and samples ranged from a single case study to national representative samples (N = 2512).
There are also variations in the number of the symptom items in the second part of the ADNM in the reviewed AjD ICD-11 studies. Four versions of ADNM were used in studies: the brief 6-item ADNM-6, 8-item ADNM-8, 20-item ADNM-20, and 29-item ADNM-29. Six of the reviewed studies used the 20-item ADNM-20 scale, which included the 20 symptom items comprising six subscales: preoccupation (four items), failure to adapt (three items), avoidance (four items), depression (three items), impulsivity (three items), anxiety (two items) (Glaesmer et al., 2015;Lorenz, Hyland, Perkonigg, & Maercker, 2017;Lorenz et al., 2016;Mahat-Shamir et al., 2017;Zelviene et al., 2017). The 29item ADNM-29 was used in one study . However, the authors of this study reduced number of items to 20 in the analysis of data. A brief 8-item ADNM-8 symptom scale with a two main AjD symptoms: failure to adapt (four items), and preoccupation (four items) was used in two studies Horn & Maercker, 2016), and a short 6-item ADNM-6 was used in a case study by Maercker, Bachem, Lorenz, Moser, and Berger (2015). The scoring of the ADNM is the sum of items for the total scale and subscales in all versions of the ADNM, and the 4-point Likert scale with the frequency of symptoms (1 = never, 2 = rarely, 3 = sometimes, 4 = often) is used.
Two studies particularly focused on testing the validity of the ADNM-20. Lorenz et al. (2016) analysed psychometric properties of the ADNM-20 among Swiss burglary victims (N = 80) (Lorenz et al., 2016). Cluster analysis identified three groups of individuals with low, moderate, and high AjD symptoms in this study. However, the specificity of the ADNM-20 was rather low (74%), and positive predictive value for AjD diagnosis was poor (57%) (Lorenz et al., 2016). The ADNM-20 sensitivity to change, and convergent and discriminant validity, was tested in psychopharmacological (Etifoxine and Alprazolam) AjD treatment study in South Africa . The ADNM-20 was administered to outpatients diagnosed with the DSM-IV AjD diagnosis (N = 190). The data of this study was collected at four time-points: baseline, seven-day, 28-day, and 38-day follow-up. At baseline, 78% of individuals diagnosed with DSM-IV AjD diagnosis were also classified as having AjD based on the ADNM scores. AjD symptoms measured with ADNM-20 significantly declined during treatment, Table 1. Empirical studies of ICD-11 adjustment disorder (N = 10). parallel to the decline of the depression (r = .13-.30), anxiety symptoms (r = .18-.31), and functional impairment (r = .18-.47) measured with other measures .

ICD-11 AjD symptom structure validation
Three studies tested the validity of the ICD-11 AjD symptom structure. Glaesmer et al. (2015) tested three AjD symptom structure models using a Confirmatory Factor Analysis (CFA) in a large German general population sample (N = 2512). Six symptoms of AjD: preoccupation, failure to adapt, avoidance (Av), depression (De), anxiety (Ax), and impulsivity (Im) comprising of 2-4 items each were included into the CFA analysis. CFA supported the general AjD factor, with the best fit of the first-order six-factor correlated CFA model, in contrast to a first-order single-factor CFA model, and secondorder single-factor CFA model (Glaesmer et al., 2015). However, the factors in the six-factor model were highly correlated and interpretation of this model is limited. Furthermore, the same study identified three quantitatively differing latent classes using a Latent Class Analysis (LCA) approach with low symptom, mild symptom, and moderate symptom severity (Glaesmer et al., 2015). The other AjD symptom structure validation study was conducted in the Lithuanian national representative sample (N = 831) by Zelviene et al. (2017). This study explored the structure of AjD symptoms and found that the two-factor AjD CFA model consisting of the two symptoms preoccupation and failure to adapt fitted the data best . However, the authors of this study also found that an alternative AjD symptom structure CFA model with additional Av, De, Ax, and Im symptoms also had a rather good model fit, and concluded that the AjD structure might need additional symptoms in the future to capture the full clinical picture of AjD .
A recent study in a Swiss sample of individuals affected by involuntary job loss (N = 333) provided a comprehensive assessment of the latent structure of AjD symptomatology using CFA (Lorenz et al., 2017). Seven AjD factor structure models were tested and compared: (1) five first-order AjD factor models with preoccupation, failure to adapt, affective reaction, Av, and Im factors; (2) one second-order factor with the same five factors included in one AjD second-order factor; and (3) two bifactor models with one general AjD factor in addition to the first-order factor model (Lorenz et al., 2017). An unrestricted bifactor model with a dominant general AjD factor provided the best fit. The authors suggest the plausibility of a unidimensional solution that should be subject to further studies.

ICD-11 AjD predictors
Two studies analysed factors associated with symptoms of ICD-11 AjD (Horn & Maercker, 2016;Mahat-Shamir et al., 2017). Seventy-three couples with exposure to a major stressor over the last 12months participated in a study which explored the role of interpersonal emotion regulation strategies on adjustment disorder (Horn & Maercker, 2016). The study found that interpersonal co-brooding and depressive symptoms were significantly associated with symptoms of AjD, supporting the importance of interpersonal social factors in AjD (Horn & Maercker, 2016).
The second study explored AjD predictors following the terror attack in Tel Aviv (N = 379) (Mahat-Shamir et al., 2017). Previous traumatic exposure was a significant predictor of PTSD and AjD, while previous exposure to stressful events during the past month was significant predictor for AjD, but not PTSD. Physical proximity to the terror event was a significant risk factor for PTSD, but not for AjD (Mahat-Shamir et al., 2017). Age was a significant predictor of AjD in this study.

Intervention studies of ICD-11 AjD
Three studies reported outcomes of cognitive behavioural (CBT) self-help interventions for ICD-11 AjD Maercker et al., 2015). One of the reviewed studies included a sample of patients in psychopharmacological treatment . However, the main aim of this study was validation of the ADNM instrument and not treatment outcomes. Furthermore, this study used DSM-IV classification for AjD diagnosis .
A group at the University of Zurich developed a self-help printed manual for burglary victims which could be delivered without therapist support Maercker et al., 2015). This lowintensity intervention has a specific focus on the ICD-11 AjD core symptoms: preoccupation and failure to adapt. There are four modules of exercises in this intervention: 'Sense of self', 'Coping', 'Activation', and 'Relaxation'. A case study indicated feasibility of this approach with a significant decline of AjD symptoms at the three-month follow-up . A waiting list RCT study with three-month follow-up (intervention group n = 30, waiting list n = 25) revealed promising findings, with between-group effect size of d = 0.67 for preoccupation, and d = 0.34 for failure to adapt symptoms . The authors of the intervention proposed that an e-health self-help approach might be suitable for an AjD .
The second AjD intervention is the self-help unguided internet-delivered Brief Adjustment Disorder Intervention (BADI) developed by a Vilnius University group in Lithuania Skruibis et al., 2016). The BADI intervention has four modules with three exercises in each of the modules, including relaxation, daily activity planning, interpersonal relationship conflict management, and mindfulness. Participants of this intervention have access to all the modules and exercises after registration online, and can freely choose which exercises and how often they want to use it. This low intensity ICD-11 AjD intervention can be used without therapist support. Findings of the recent study (N = 1077) revealed moderate effect sizes (d = 0.53-0.64) of the BADI intervention on AjD symptoms in this study . Furthermore, additional psychologist support was not contributing significantly to the outcomes of the intervention, indicating that internet-delivered self-help AjD interventions could be considered as a promising alternative in the treatment of AjD .

Discussion
Proposals to update the definition of AjD for ICD-11 (Maercker et al., 2013) received attention in research since the introduction of new AjD symptoms in 2013. We identified 10 empirical ICD-11 AjD studies in our review with adult samples from Germany, Lithuania, Israel, the Republic of South Africa, and Switzerland. These studies analysed the AjD factor structure, measurement validity, risk factors for AjD, and outcomes of AjD interventions.
To the best of our knowledge, the only ICD-11 based measure currently available is the Adjustment Disorder New Module (ADNM) (Einsle et al., 2010) which was used in all 10 reviewed studies. The validity of the ADNM has been tested in two studies Lorenz et al., 2016). The ADNM measure, however, also includes symptoms that are associated with a previous definition of AjD in ICD-10, such as anxiety and depression symptoms. Furthermore, there is a big variation in the number of the ADNM items across all the studies, limiting comparison of the findings. Further validation of the ADNM, with test-retest reliability analysis and cross-cultural studies, or the development of a new more appropriate measure is needed.
The findings on the AjD symptom structure as proposed for the ICD-11 are ambiguous. We found only three ICD-11 AjD symptom structure validity studies using the CFA approach. The Lithuanian study supported a two-factor AjD symptom structure , but an alternative model with more symptoms was reported as feasible. The study of a German sample found that a correlated six-factor solution was the most applicable (Glaesmer et al., 2015). A recent Swiss study supported the unidimensional structure of AjD symptoms (Lorenz et al., 2017). So far, empirical data do not provide enough support for the ICD-11 definition of AjD symptom structure. None of the analysed studies attempted to compare ICD-10 and ICD-11 AjD diagnostic criteria. Further studies of AjD symptom structure in other samples, and particularly in clinical groups, are needed.
The study of AjD risk factors reveals the importance of the nature of stressful event. In line with proposals for the ICD-11, PTSD was predicted by the previous traumatic experiences, but not by the exposure to a stressful event in the past month. AjD was predicted both by stressful experiences and previous trauma exposure in the same study (Mahat-Shamir et al., 2017). Furthermore, demographic characteristics, such as age, and interpersonal factors, such as emotional regulation, seem to be important for AjD (Horn & Maercker, 2016;Mahat-Shamir et al., 2017). Furthermore, initial findings indicate that AjD can also be associated with traumatic experiences (Mahat-Shamir et al., 2017;O'Donnell et al., 2016), and this should be explored in further studies.
Only a few AjD intervention studies were available prior to the ICD-11 proposals (Casey & Bailey, 2011). After the ICD-11 proposals (Maercker et al., 2013), there is still very limited data available on treatment of ICD-11 AjD. Two RCT studies indicated promising effects of the specialized CBT-based self-help interventions targeted towards symptoms of ICD-11 AjD Eimontas et al., 2017). An internet-delivered approach might be suitable for treatment of AjD Maercker et al., 2015).

Future perspectives
The position of AjD among other mental disorders remains largely unclear. Looking at AjD dimensionally from a general psychopathology factor perspective (Stephan et al., 2016), we could assume that AjD could be placed at the lower end of the psychopathology continuum. The most recent proposals for ICD-11 AjD definition place AjD as a clinical category 'below' other mental disorders, stating that AjD could be diagnosed only if another mental disorder is not diagnosed based on symptom intensity (WHO, 2017).
Even if AjD would be diagnosed based on an exclusion criterion when the symptoms of an individual do not fully meet criteria of another disorder, such as PTSD or depression, clinicians and researchers need measures to identify if AjD symptoms are clinically significant. A recent survey of mental health practitioners indicated that clinicians are having difficulties with ICD-11 AjD symptom identification (Keeley et al., 2016). The ICD-11 definition provides a new platform for the development of AjD symptom measures to help clinicians to deal with difficulties associated with diagnosing AjD. The available ADNM measure needs further validation in clinical samples and in a cross-cultural context to be truly useful for clinicians. Structured diagnostic interview of ICD-11 AjD symptoms is needed. Further development of AjD measures will be a challenging task, complicated by the diversity of life-stressors which cause AjD. It could be that different cut-off scores of measures for AjD diagnosis across various population and different stressors will be developed. Diagnostic research criteria for the ICD-11 AjD diagnosis could facilitate research in this field and should be developed in the near future.
The optimal treatment approach of AjD remains largely unclear. There are no AjD evidence-based treatment guidelines available so far. AjD symptoms can last for six months or more if the stressor persists, based on the ICD-11 definition. We could expect diverse symptom trajectories in association with stressful situational developments. AjD symptoms might become more severe if a stressor becomes more severe, and AjD symptoms could decrease if the stressful situation is resolved, e.g. an individual finds a job after a prolonged period of unemployment. If AjD symptoms persist, health care providers need to take the responsibly of providing the best treatment available. We expect that the ICD-11 AjD definition with a proposed new symptom profile can facilitate AjDfocused specialized treatment developments. The first developments of ICD-11 AjD-focused interventions from Switzerland and Lithuania show encouraging outcomes. CBT appears to be promising for treatment of AjD based on the available evidence, however, CBT is the only approach tested so far in the ICD-11 AjD treatment. Low intensity self-help AjD interventions, and internetdelivered AjD interventions could be the most cost-effective solutions for health care and useful for clinicians.
The two mental disorders diagnostic classifications are used worldwide in healthcare: DSM and ICD. We focused on the ICD-11 AjD studies in our review. However, the DSM-5 definition of AjD (American Psychiatric Association, 2013) differs significantly from the AjD description in the ICD-11 (WHO, 2017). The major difference of the AjD definition in DSM-5 is a broader definition of AjD without description of clearly defined symptoms and inclusion of AjD subtypes in contrast to the ICD-11. A study by  found 78% concordance in the DSM-IV and the ICD-11 AjD diagnosis, indicating that the DSM and the ICD have similarities in AjD criteria. However, incongruences in major diagnostic classifications in the future could result in a diverse understanding of AjD across different countries and professionals, depending on their use of the DSM versus the ICD in clinical practice and research.
We conclude that updates of AjD definition in ICD-11 could significantly contribute to the advancement of AjD understanding. Still, there is a need for more studies and insights from clinical practice to move the field of AjD research and practice forward.

Disclosure statement
No potential conflict of interest was reported by the authors.