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(p. 1) Evidence-Based Treatments and the Atypical/Complex Conundrum 

(p. 1) Evidence-Based Treatments and the Atypical/Complex Conundrum
(p. 1) Evidence-Based Treatments and the Atypical/Complex Conundrum

Jenna L. Schleien

, Gina Dimitropoulos

, Katharine L. Loeb

, and Daniel Le Grange

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date: 21 March 2018

“Real-world” eating disorder presentations rarely fit neatly into the diagnostic categories defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM). It is generally understood by those involved in the diagnosis, study, or treatment of eating disorders that these are heterogeneous entities because great variation is found in symptom presentations and affected populations. Disordered eating presentations that are comorbid with other mental disorders, that do not map directly onto current diagnostic criteria, and that occur in atypical populations are more frequently seen in clinical practice than they are attended to in the literature. This chapter provides an overview of the evolution of the diagnostic and treatment approach of atypical and complex eating disorders and illuminates the mismatch between clinical presentations and evidence-based interventions. First, this chapter introduces the conundrum of applying controlled treatment studies to atypical and complex comorbid eating disorder presentations. Then, it examines atypical eating disorder presentations, followed by complex comorbid eating disorder presentations. It also reviews proposed solutions to the atypical/complex eating disorder “problem.” Last, it discusses future directions relevant to atypical and complex eating disorder presentations and current challenges surrounding the development and implementation of targeted interventions.

(p. 2) The Conundrum of Applying Controlled Treatment Studies to Atypical and Complex Presentations

The most robust approach for assessing treatment effectiveness includes the random allocation of individuals to conditions; adequate sample sizes to ensure sufficient statistical power; a clearly defined intervention with monitoring of fidelity of implementation; and outcome measures that are theoretically and clinically relevant, ecologically valid, and carried out blind to treatment group (Maughan, 2013). One method of meeting these stringent criteria is the use of randomized controlled trials (RCTs), considered the gold standard for intervention studies (Maughan, 2013; Salmond, 2008; Wiebe & Hill, 2011). In an RCT, each participant has the same random or near-random chance of being assigned to each condition as the next participant (Wiebe & Hill, 2011). Furthermore, RCTs are controlled, which isolates the effect of the intervention by ruling out confounding variables (Salmond, 2008). In this way, RCTs are more precise and accurate assessments of treatment modalities than anecdotal reports or uncontrolled case series (Correll, Kishimoto, & Kane, 2011). As rigorous evaluations of cause and effect, RCTs are critical in illuminating the effectiveness of different treatment modalities.

Although RCTs are widely considered the highest quality research design for intervention studies, their integrity and success are not guaranteed (Salmond, 2008; Wiebe & Hill, 2011). Good RCTs are tightly controlled, which includes a thorough identification of potential confounding factors (Salmond, 2008) and randomizing whenever possible to ensure the equivalence of the comparison groups on all factors but the intervention (Kerlinger & Lee, 2000). In addition, tightly controlled RCTs include clear but simple eligibility criteria that promote a narrow focus on groups with specific characteristics (e.g., symptoms) in common (Wiebe & Hill, 2011). In RCTs designed to test various forms of eating disorder treatment, participants commonly meet criteria for the same DSM-defined disorder or spectrum thereof and may fall within a defined range for age or body mass index. In addition, participants are typically excluded if they have other psychiatric conditions requiring immediate treatment (e.g., major depression with suicidality, schizophrenia, and acute medical complications) and if they have already been treated with the form of psychotherapy being tested. Restricted inclusion criteria provide an RCT with high internal validity, but these stringent criteria are also associated with limited external validity, making the results much less generalizable to the heterogeneous populations seeking treatment (Correll et al., 2011), including atypical eating disorders. Furthermore, RCTs tend to be conducted on majority samples (i.e., White, middle-class women), further limiting external validity. In addition, there is a scarcity of knowledge about the response to treatment in patients with complex presentations, such as comorbid emergent disorders (Correll et al., 2011). Stringent inclusion criteria, considered paramount to a good RCT, have created challenges because limited research has been conducted with the atypical and complex eating disorder populations that (p. 3) make up a sizeable portion of treatment-seeking, clinical samples. Furthermore, the degree to which treatments based on RCTs can be applied or will be effective with atypical and complex populations is questionable. This renders evidence-based clinicians much less well equipped in devising treatment approaches for these individuals. There is no simple solution. However, as discussed later in this chapter, the body of literature on evidence-based interventions for atypical populations is growing.

Just as RCTs are critical in demonstrating the effectiveness of treatment modalities for atypical disordered eating presentations, they are equally important for complex comorbid presentations. Although challenging, these RCTs are possible to conduct. For instance, individuals with suicidality are typically excluded from RCTs, but research has shown that suicidality is a feasible target for RCTs with proper clinical attention, safeguards, and intervention (Linehan et al., 2015; March et al., 2007; Meltzer, 2002). This suggests that complex presentations such as comorbid eating disorders and suicidality, or other acute issues previously excluded from RCTs, can be included in well-designed RCTs with a multimodal intervention. Other presentations that are frequently comorbid with eating disorders and that do not necessarily constitute acute risk (e.g., depression, obsessive–compulsive disorder, and mild substance use) pose fewer problems and typically permit a primary focus on the eating domain. Another way to study atypical and/or complex populations is by examining moderators within the context of RCTs. Specifically, severity and complexity of eating disorder presentations may moderate treatment outcomes. In an RCT comparing family-based treatment (FBT) and adolescent-focused therapy (AFT) for anorexia nervosa (AN), Le Grange and colleagues (2012) found that eating-related obsessionality and eating disorder-specific psychopathology moderated end-of-treatment outcomes such that individuals with higher baseline scores on these indices benefitted more from FBT than from AFT. An RCT comparing dosage of family therapy for adolescent AN concluded that individuals with more severe and persistent eating-related obsessive–compulsive thinking, as well as individuals from non-intact families, received greater benefit from long-term therapy (Lock, Agras, Bryson, & Kraemer, 2005). Based on these results, it is possible that complex eating disorder presentations may benefit more from a higher dose of FBT or a combination of different treatment modalities such as FBT and dialectical behavior therapy (DBT).

Atypical Eating Disorder Presentations

Diagnostic criteria for eating disorders have evolved over iterations of the DSM, reflecting shifting notions of what constitutes an eating disorder. The third edition of the DSM (DSM-III; American Psychiatric Association [APA], 1980) formally recognized two categories of eating disorders: AN and bulimia nervosa (BN). DSM-III eating disorders could also be classified as “atypical,” which was intended to “indicate a category within a class of disorders that is residual to the specific categories in that class” (APA, 1980, p. 32). This served as an acknowledgment (p. 4) that not all disordered eating presentations seen in clinical practice could be covered by DSM-III diagnostic criteria. The revision of DSM-III (DSM-III-R; APA, 1987) further refined the diagnostic criteria for eating disorders, for example, by including a minimum frequency of binge-eating episodes for BN. In the fourth edition of the DSM (DSM-IV; APA, 1994), the “atypical” classification advanced into an eating disorder not otherwise specified (EDNOS) category, which was added to capture all other clinically significant disordered eating that did not meet criteria for AN or BN. In addition, the subclassification into restricting and binge-eating/purging types was added to criteria for AN. Criteria for binge-eating disorder (BED) were also provided in the appendix of DSM-IV as an example of EDNOS and a category in need of further study (APA, 1994). BED was officially added as its own diagnostic category in DSM-5 (APA, 2013). In addition to AN, BN, and BED, the DSM-5 feeding and eating disorders category currently includes pica, rumination disorder, and avoidant/restrictive food intake disorder (ARFID; APA, 2013).

Across iterations of the DSM, subsets of atypical eating disorders, such as BED, have ultimately found “homes” as primary diagnostic categories. This reflects an evolution in our increasing recognition that atypical presentations are, in fact, increasingly typical. Nonetheless, many eating disorder presentations continue to be classified in catch-all categories such as EDNOS. DSM-IV to DSM-5 reflected a shift in the name of this category from EDNOS to other specified feeding or eating disorder (OSFED; APA, 1994, 2013).

According to DSM-5, OSFED applies to presentations in which symptoms characteristic of a feeding and eating disorder that cause clinically significant distress or impairment in social, occupational, or other important areas of functioning predominate (APA, 2013). At the same time, these symptoms do not meet the full criteria for any of the disorders in the feeding and eating disorders diagnostic class (APA, 2013). It is important to note that the name of this category recently changed from EDNOS to OSFED, and most of the research to date has been done on EDNOS according to DSM-IV criteria (APA, 1994). Therefore, research using OSFED criteria will capture fewer cases now that more have presumably been absorbed into newer AN and BN categories, as well as ARFID. For the purposes of this chapter, the term EDNOS is used when DSM-IV criteria were utilized in the research, and the term OSFED is used when DSM-5 criteria were utilized (APA, 1994, 2013).

Research suggests that EDNOS represents a majority of patients presenting for treatment (Striegel-Moore, Wonderlich, Walsh, & Mitchell, 2011). DSM-5 has been demonstrated to decrease the prevalence of OSFED in treatment-seeking (Birgegard, Norring, & Clinton, 2012; Fairburn & Cooper, 2011) and community samples (Keel, Brown, Holm-Denoma, & Bodell, 2011; Machado, Gonçalves, & Hoek, 2013; Stice, Marti, & Rohde, 2013), but OSFED prevalence rates remain at 15–30% of cases (Allen, Byrne, Oddy, & Crosby, 2013).

Atypical presentations do, in fact, share some common features. The majority of these cases have clinical features that resemble AN and BN but at different levels or in various combinations (Crow, Agras, Halmi, Mitchell, & Kraemer, 2002; (p. 5) Fairburn et al., 2007; Waller, 1993). Furthermore, most disordered eating presentations include an overvaluation of shape and weight (including its manifestation, such as body checking and extreme feelings of fatness), persistent attempts to follow stringent dietary rules, weight-control behavior (e.g., self-induced vomiting, excessive exercise, and laxative misuse; Fairburn & Cooper, 2011), low self-esteem, and mood intolerance in the presence of binge eating (Lampard, Tasca, Balfour, & Bissada, 2013). In other words, individuals with atypical presentations tend to exhibit disabling concern over eating, shape, and weight (Turner & Bryant-Waugh, 2004). Despite shared features, these presentations are naturally heterogeneous. Presentations differ in demographics (e.g., ethnicity and educational level), eating disorder symptoms (e.g., the presence and frequency of binge eating, self-induced vomiting, laxative use, diuretic use, and fasting), and comorbid psychopathology (Binford & Le Grange, 2005; Crow et al., 2002). It has also been suggested that they differ in the extent to which affected individuals succeed in undereating, which consequently leads to variation in weight (Fairburn & Cooper, 2011).

It is apparent that there are some similarities and differences among atypical presentations. As Walsh and Kahn (1997) wisely highlighted, “we study what we define” (p. 369). Therefore, little is known about the course, outcome, or treatment of atypical presentations because they are, by definition, not demarcated in distinct DSM categories. Consequently, individuals with EDNOS/OSFED are typically excluded from research (Fairburn & Bohn, 2005). Even studies that include atypical presentations tend to vary in their definitions of what constitutes EDNOS/OSFED (Keel, Brown, Holland, & Bodell, 2012). The research that has been conducted suggests that atypical eating disorder cases are no different than typical cases in terms of severity of pathology, degree of secondary psychosocial impairment, and outcomes (Castellini et al., 2011; Fairburn et al., 2007; Grilo et al., 2007; Keel, Gravener, Joiner, & Haedt, 2010; Ricca et al., 2001; Turner & Bryant-Waugh, 2004). In addition, despite the relative stability of the overarching categorization of eating disorders, there is a great deal of cross-diagnostic flux because many patients with OSFED go on to meet full eating disorder criteria (Castellini et al., 2011; Herzog, Hopkins, & Burns, 1993; Milos, Spindler, Schnyder, & Fairburn, 2005). High diagnostic crossover may suggest that current classification schemes distinguish between various phases of a single disorder rather than between different disorders. DSM utilizes a categorical approach to describe psychopathology, in which eating disorders are classified into discrete categories. Some researchers and theorists have also proposed incorporating dimensional models into eating disorder classification, in which one or more dimensions underlie a continuum of eating disorders (Wildes & Marcus, 2013; Williamson, Gleaves, & Stewart, 2005). For instance, research suggests that the cognitive correlates of disordered eating (e.g., body dissatisfaction and drive for thinness) are dimensional, in that they are continuous with normality and thus represent varying degrees of impairment or severity (Holm-Denoma, Richey, & Joiner, 2010). Discussion about categorical versus dimensional approaches to eating disorder taxonomy continues to exist (Williamson et al., 2005).

(p. 6) Atypical Demographic Presentations

There are limited specific data indicating whether current treatments adequately address any potential unique needs of diverse populations such as individuals with eating pathology beginning in midlife, males, people with different sexual orientations, children, individuals from diverse cultural backgrounds, and athletes. Disordered eating presentations in these populations are complicated by person-level factors such as gender, aging, and sexual orientation. These factors may generate additional issues in therapy relevant to formulation, the understanding of maintaining variables, and consequent levels of intricacy to treatment.

The erroneous perception that AN and BN predominantly affect Caucasian, adolescent females from privileged economic backgrounds contributes to community-based clinicians overlooking those who do not fit this stereotype and not providing appropriate referrals and needed treatment in a timely manner. RCTs commonly include adolescent or young adult Caucasian females and neglect patients of different ages, ethnic backgrounds, or sexual orientations. For example, despite increasing numbers of RCTs in adolescent populations, few RCTs have been devoted specifically to diverse populations, with the exceptions of samples of gay men at high risk of developing eating disorders recruited from the community (Brown & Keel, 2015), ethnic minorities presenting with bulimia nervosa (Chui, Safer, Bryson, Agras, & Wilson, 2007), ethnic minorities presenting with BED (Thompson-Brenner et al., 2013), and ethnic minorities recruited from the community (Stice, Marti, & Cheng, 2014). It is important to not only increase mental health literacy about atypical eating disorders but also educate health and mental health care professionals that a diversity of individuals including males, older individuals, and those from diverse ethnic, racial, and economic backgrounds are vulnerable to OSFED, purging disorders, and muscle dysmorphia (Cohn, Murray, Walen, & Wooldridge, 2016; Murray & Anderson, 2015).

Complex Eating Disorder Presentations

Complex presentations include eating disorders occurring with other significant psychiatric issues and comorbidities, such as trauma, substance use, self-harm and suicidality, personality disorders, body dysmorphic disorder, autism spectrum disorder, and anxiety. Between 20% to 95% of patients with eating disorders are also afflicted with comorbid psychiatric disorders, the most common being mood, anxiety, obsessive–compulsive, and substance use disorders (Blinder, Cumella, & Sanathara, 2006; Bühren et al., 2014; Herzog, Keller, Sacks, Yeh, & Lavori, 1992; Hudson, Hiripi, Pope, & Kessler, 2007; Kaye, Bulik, Thornton, Barbarich, & Masters, 2004; Milos, Spindler, & Schnyder, 2004; Spindler & Milos, 2004; Ulfvebrand, Birgegård, Norring, Högdahl, & von Hausswolff-Juhlin, 2015; Zaider, Johnson, & Cockell, 2000). The application of (p. 7) a protocol designed only for an eating disorder to a case with complex comorbidities is often completely inadequate. Thus, clinicians need guidance on how to select, sequence, and implement treatment for psychiatric comorbidities. Unfortunately, very few RCTs exist that are designed to examine treatments of eating disorders with psychiatric comorbidities. There are a few notable exceptions in substance use (Courbasson, Nishikawa, & Dixon, 2012; Courbasson, Nishikawa, & Shapira, 2011) and borderline personality disorder (Thompson-Brenner et al., 2016).

Clinical decision algorithms are an important tool for clinicians in the treatment of patients with eating disorders. A crucial question germane to the treatment of these patients is whether to address both disorders simultaneously or, if not, which disorder to treat first. These questions are important because sequential treatment may lead to worsening or relapse of symptoms in one disorder as the other improves (Courbasson, Smith, & Cleland, 2005), and symptoms from the untreated disorder may interfere with recovery from the disorder being treated first (Sutherland, Weaver, McPeake, & Quimby, 1993). For example, although many suggestions have been made for concurrent treatment of eating and substance use disorders with cognitive–behavior therapy (CBT; Grilo, Sinha, & O’Malley, 2002; Sinha & O’Malley, 2000; Sysko & Hildebrandt, 2009) and DBT (Grilo et al., 2002), empirically validated clinical decision algorithms do not exist. However, the research that does exist suggests that both disorders can be treated successfully and simultaneously with DBT (Courbasson et al., 2012) and mindfulness-action based CBT (Courbasson et al., 2011). Similarly, for comorbid eating disorders and obsessive–compulsive disorder, one study showed that they can be treated simultaneously and effectively with a cognitive–behavioral approach emphasizing exposure and response prevention (Simpson et al., 2013).

A stepped care approach is one way to think about how, and in what order, to best treat comorbid conditions. In a stepped care approach, treatments are provided in sequential order according to patient need and available treatment resources (Wilson, Vitousek, & Loeb, 2000). This approach has been proposed as an effective way to treat BN and BED, particularly because treatments can be costly in terms of time and money, in addition to unnecessarily invasive (Fairburn, Agras, & Wilson, 1992; Gamer & Needleman, 1997; Wilson et al., 2000). The starting point is the simplest, least intrusive, and least costly treatment (e.g., guided self-help), and more complex or intensive interventions are provided if the patient does not respond (e.g., fluoxetine and then individual therapy) (Mitchell et al., 2011; Wilson et al., 2000). Stepped care models have been shown to be efficacious for BN (Davis, McVey, Heinmaa, Rockert, & Kennedy, 1999; Mitchell et al., 2011; Palmer, Birchall, McGrain, & Sullivan, 2002; Treasure, Schmidt, Troop, & Todd, 1996). Importantly, this approach appears to be cost-effective compared to individual CBT (Crow et al., 2013). A stepped care model validated by research could guide clinicians in how to best treat eating disorders with psychiatric comorbidities in a way that is both cost-effective and individually tailored.

(p. 8) Proposed Solutions to the Atypical/Complex Eating Disorder “Problem”

Notwithstanding some knowledge about the course, outcome, and treatment of atypical and complex eating disorder presentations, considerable gaps in the literature remain regarding their similarities and differences. With the current framework, an abundance of unspecified, atypical presentations is unaccounted for, rendering the controlled study of heterogeneous presentations difficult and evidence-based practice with these populations challenging. Although none of them solve this “problem” completely, diverse solutions have been proposed to the issue of how to parse out atypical presentations. Some suggest small alterations to existing DSM criteria under the premise that criteria are too strict (Watson & Andersen, 2003; Wilson & Sysko, 2009). This solution would entail reclassifying some cases of OSFED into existing DSM categories. DSM-5 was responsive to some of these previously proposed, research-supported alterations, including removing amenorrhea from the AN diagnostic criteria, raising the weight threshold for AN (Watson & Andersen, 2003), and lowering the frequency threshold for binge eating and purging for BN (Wilson & Sysko, 2009). A second proposed solution is selecting some atypical cases and placing them in new diagnostic groups, as has historically occurred with BED and ARFID (as described previously). Presentations that have been proposed and are currently under study include night eating syndrome, purging disorder, AN with a history of obesity, muscle dysmorphia, and specific phobia of vomiting, which are discussed in detail in other chapters in this book.

A third potential solution is to invent and validate new diagnostic schemes. For example, Walsh and Sysko (2009) introduced a scheme called “broad categories for the diagnosis of eating disorders,” which consists of the hierarchical categories of AN and behaviorally similar disorders, BN and behaviorally similar disorders, BED and behaviorally similar disorders, and EDNOS. The authors state that this classification system would substantially reduce the size of the EDNOS category while providing other advantages, such as accurate diagnosis in settings in which a comprehensive psychiatric assessment is not feasible. Alternatively, Fairburn and Cooper (2011) offer the option of subdividing eating disorder cases based on their dominant clinical feature, which would produce two groups: one characterized by recurrent weight control methods (i.e., self-induced vomiting and laxative misuse), often accompanied by subjective binge eating, and another that includes attempts to follow extreme dietary rules. The authors note that the former has been termed “purging disorder” and that the latter may be best labeled “restrained eating disorder.” Some have even queried if the field should move away from diagnosis altogether or, less radically, migrate to a “scientist–practitioner” model of eating disorders (Waller, 1993). The goal of the scientist–practitioner model (Barlow, 1981) is to bridge the gap between research and clinical work. An eating disorder conceptualization would include the variance in symptoms common to all individuals afflicted (e.g., general concern with control over food, weight, and body shape), the variance unique to the individual (e.g., history of low weight), (p. 9) and the variance that applies to some clusters of sufferers (e.g., body image distortion). Fourth, statistical methods such as cluster analysis, latent profile analysis, taxometric analysis, and Q-analysis of clinicians’ opinions have also been used to yield clinically relevant groupings (Keel, Crosby, Hildebrandt, Haedt-Matt, & Gravener, 2013; Mitchell et al., 2007; Turner, Bryant-Waugh, & Peveler, 2009; Westen & Harnden-Fischer, 2001). Accordingly, some argue that eating disorder classification may be improved by including dimensional assessments in the current categorical scheme because evidence suggests that eating disorders vary in severity along a continuum in addition to type (Wildes & Marcus, 2013; Williamson et al., 2005). This idea resonates with the recent initiative of the National Institute of Mental Health, the Research Domain Criteria (RDoC), which is a call to investigate the phenotypic dimensional structure of psychopathology. In this way, RDoC is an attempt to understand the full range of human behavior by considering both psychology and biology in the understanding and classification of mental disorders (Insel et al., 2010).

In addition to the RDoC, the transdiagnostic framework may be employed to help with the goal of understanding the maintaining factors that connect or distinguish disorders. In 2003, Fairburn, Cooper, and Shafran introduced a transdiagnostic theory of disordered eating intended to supplement the cognitive–behavioral theory of BN and expand it to broad disordered eating. Fairburn and colleagues argue that in addition to a dysfunctional system for evaluating self-worth, a combination of clinical perfectionism, core low self-esteem, mood intolerance, and interpersonal difficulties maintains eating pathology in certain patients. Derived from this newly proposed transdiagnostic theory is a unified treatment plan that targets the core psychopathology of eating disorders called enhanced cognitive–behavior therapy (CBT-E; Fairburn, 2008). Hence, the transdiagnostic approach allows for the development and use of treatment protocols that can assist individuals with a range of eating disorder presentations that are all functionally impairing or causing clinically significant distress.

In some ways, the transdiagnostic approach has effectively addressed the former gaps in the literature (Fairburn, 2008; Fairburn et al., 2003). Most important, a transdiagnostic approach better reflects clinical realities, given the sheer number of patients with atypical eating disorders presenting for treatment (Fairburn, 2008). A transdiagnostic theory and treatment approach also allows for the effective treatment of all eating disorders with an emphasis on understanding and addressing common maintaining factors (Fairburn, 2008; Fairburn et al., 2003). Clinicians thus have an evidenced-based intervention at their disposal that matches the range of clinical presentations, and they are not left questioning how best to treat their patients who do not fit primary DSM diagnostic categories. The transdiagnostic approach is also sensitive to a developmental perspective. It removes the necessity of awkwardly applying DSM criteria to children and adolescents (Loeb et al., 2011), who often present atypically as eating disorders emerge (Workgroup for Classification of Eating Disorders in Children and Adolescents [WCEDCA], 2007). Children and adolescents regularly fail to meet diagnostic criteria for reasons both similar to and different (p. 10) from those of adults, including developing abstract thinking skills necessary to self-recognize and endorse aspects of psychological criteria for eating disorders (WCEDCA, 2007).

On the other hand, the transdiagnostic approach is imperfect. For example, in reference to his “trans-transdiagnostic” model, Waller (2008) argues that eating disorders should be relocated in the broader category of anxiety disorders for reasons including the high degree of comorbidity between anxiety and eating disorders, the frequent antecedence of anxiety to eating concerns (Bulik, Sullivan, Fear, & Joyce, 1997; Swinbourne et al., 2012), and the fact that actions frequently characteristic of eating disorders (e.g., food restriction, binging, purging, and body checking) can be viewed as safety behaviors that reduce anxiety in the short term (Pallister & Waller, 2008). In addition, the transdiagnostic approach assumes a common set of maintaining factors, but differences have been shown, particularly between AN and BN, in factors such as disease course (e.g., diagnostic crossover), prognostic indicators, outcome (e.g., remission and mortality rates) (Keel & Brown, 2010), and neurobiological and neurocognitive factors (Van den Eynde et al., 2011; von Hausswolff-Juhlin, Brooks, & Larsson, 2015; Zucker, Moskvich, & Soo, 2011; Zucker et al., 2007). The transdiagnostic approach has also been criticized for having the potential to de-emphasize the seriousness of AN and consequently shrink funding for treatment (Birmingham, Touyz, & Harbottle, 2009). In essence, however, although a multitude of solutions have been proposed in attempting to accommodate the challenges presented in the recognition and treatment of atypical and complex presentations, no one has, as yet, clearly informed treatment guidelines in these populations.

Conclusion and Future Directions

It is important to continue to clarify our conceptualization of eating disorders in terms of psychological, sociocultural, and neurobiological factors that may be shared or distinct between different presentations. The eating disorder field is in pressing need of more unification in its evidence-based applications and treatment decision algorithms so that clinicians can best serve individuals with both atypical and complex presentations. Research should strive to be clinically relevant, which will depend on posing appropriate questions and answering them in a way that is both interesting and easily digestible (Waller, 1993). As described previously, RCTs should be conducted to provide information about treatment moderators and outcomes for individuals with atypical presentations, atypical demographics, or complex comorbid presentations. Although RCTs remain the gold standard of empirical cause-and-effect treatment research, meaningful and scientifically rigorous information can also be derived from clinically oriented research methods such as single-case designs, patient series designs, qualitative methods, and quasi-experimental designs (Waller, 1993). Consistent with a scientist–practitioner model (Barlow, 1981), a primary goal of the eating disorders field should be to bridge the gap between research and clinical work.

(p. 11) The body of literature on evidence-based interventions for atypical and complex populations is growing. For example, two RCTs have been conducted in outpatient transdiagnostic samples of adult patients who had an eating disorder but were not markedly underweight (Fairburn et al., 2009) and with adult patients with any form of eating disorder (Fairburn et al., 2015). In addition, two noncontrolled studies have shown that CBT-E for adults with a full range of eating disorders (Byrne, Fursland, Allen, & Watson, 2011) and for adults with bulimia and atypical eating disorders (Knott, Woodward, Hoefkens, & Limbert, 2015) is generalizable to treatment in a clinical context.

In addition to conducting research with broad transdiagnostic samples, it may also be beneficial to delineate between atypical presentations so that targeted research protocols can be developed and tested. Some research has endeavored accordingly. RCTs have shown varying degrees of success with treatment for night eating syndrome (Pawlow, O’Neil, & Malcolm, 2003; Wal, Maraldo, Vercellone, & Gagne, 2015). However, there is a dearth of research on other presentations such as specific phobia of vomiting or purging disorder, or even ARFID and rumination disorder, both of which are primary diagnoses in DSM-5. It may be helpful to further divide atypical presentations into new diagnostic groups, as is being done with night eating syndrome, purging disorder, AN with a history of obesity, muscle dysmorphia, and specific phobia of vomiting.

Evidence-based treatment research for atypical and complex eating disorders is challenging to conduct and interpret. For one, inclusion/exclusion criteria for atypical and complex presentations vary, making it difficult to generalize to a truly transdiagnostic sample. The heterogeneity inherent in a transdiagnostic sample is good for ecological validity and generalizability of results, but there will be many individuals to whom the results may not be applicable. Another significant hurdle is that outcome variables in these studies will be less uniform than those in studies focusing on a single type of disorder because definitions of success vary across presentations. That is, quantifying recovery across presentations is imprecise. This has been resolved in transdiagnostic treatment studies with measures that equalize pathology among multiple presentations, such as by using a global Eating Disorder Examination interview score (EDE, 16th edition; Fairburn, Cooper, & O’Connor, 2008) as a measure of severity of eating disorder features or using a score less than one standard deviation above the community mean to define remission (Fairburn et al., 2015). In this way, it is crucial to compare the normalization of eating pathology to community, as opposed to clinical, samples. Normative comparisons such as this have been commonly used to quantify and classify clinically significant change (Kazdin, 2003; Kendall, Marrs-Garcia, Nath, & Sheldrick, 1999).

There are myriad challenges for clinicians and patients alike in terms of adherence to evidence-based treatment in the context of complex and atypical presentations and populations. A lack of diagnostic clarity in atypical cases may make it more tempting for clinicians to attend to broader concerns and lose sight of eating disorder treatment protocol. In addition, adherence is difficult in cases with competing, clinically significant comorbidities. This may be especially challenging for (p. 12) clinicians who are not as practiced with manual-based treatments. Particularly without validated clinical decision algorithms, addressing comorbid disorders is an added challenge to remaining focused on the treatment protocol. Without evidenced-based manuals or guidelines to follow, therapists may feel lost, ineffective, or anxious, which may negatively affect the therapeutic relationship in a way that is detrimental to therapeutic outcomes. At the same time, patients with atypical presentations may not feel as connected to supportive communities, given that these are often based on specific diagnoses. In addition, if not assigned an official DSM diagnosis, patients and insurers alike may perceive the patients’ disorders as less severe (often unrealistically). Such factors may contribute to decreased treatment seeking and access.

In summary, the field of eating disorders has historically been plagued by a mismatch between patients seeking treatment with real-life eating disorder presentations and the dearth of evidence-based interventions and algorithms to best meet these patients’ needs. Newer models conceptualizing eating disorders in novel ways have been introduced to address this conundrum. Research is increasingly shifting to include populations of individuals with atypical and complex eating disorder presentations. As further findings emerge, clinicians will be able to more effectively serve all individuals with eating disorders.


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