Typical Versus Atypical Anorexia Nervosa Among Adolescents: Clinical Characteristics and Implications for ICD-11

Comparing changes in eating disorder psychopathology and comorbid symptoms over treatment in anorexia nervosa and atypical anorexia nervosa in a partial hospitalization program

OBJECTIVE

The objective of this study is to compare treatment trajectories in anorexia nervosa (AN) and atypical AN.

METHOD

Adolescents and adults with AN (n = 319) or atypical AN (n = 67) in a partial hospitalization program (PHP) completed diagnostic interviews and self-report questionnaires measuring eating disorder (ED), depression, and anxiety symptoms throughout treatment.

RESULTS

Premorbid weight loss did not differ between diagnoses. Individuals with atypical AN had more comorbid diagnoses, but groups did not differ on specific diagnoses. ED psychopathology and comorbid symptoms of depression/anxiety did not differ at admission between groups nor did rate of change in ED psychopathology and comorbid symptoms of depression/anxiety from admission to 1-month. From admission to discharge, individuals with atypical AN had a faster reduction in ED psychopathology and comorbid symptoms of depression and anxiety (ps < 0.05; rs = 0.01-0.32); however, there were no group differences in ED psychopathology or depression symptoms at discharge (ps>.50; ds = .01-.30). Individuals with atypical AN had lower anxiety at discharge compared to individuals with AN (p = 0.05; d = .4). Length of stay did not differ between groups (p = 0.11; d = .21).

DISCUSSION

Groups had similar ED treatment trajectories, suggesting more similarities than differences. PHP may also be effective for AAN.

PUBLIC SIGNIFICANCE

This study supports previous research that individuals with AN and atypical AN have more similarities than differences. Results from this study indicate that individuals with AN and atypical AN have similar treatment outcomes for both ED psychopathology and depressive symptoms; however, individuals with atypical AN have lower anxiety symptoms at discharge compared to individuals with AN. AN and atypical AN also have more symptom similarity at admission and throughout treatment, which challenges their current designation as distinct disorders.

Few differences in psychiatric comorbidities and treatment response among people with anorexia nervosa and atypical anorexia nervosa

OBJECTIVE

Little is known about how individuals with atypical anorexia nervosa (AN) respond to eating disorder (ED) treatment in a partial hospitalization program (PHP), nor how certain factors such as trauma, childhood abuse, psychiatric comorbidity, and suicidal thoughts and behaviors might contribute to poor treatment outcomes. Thus, the current study (1) compares prevalence of these factors between individuals with AN and atypical AN upon admission to an ED PHP, (2) compares PHP treatment response between groups, and (3) investigates whether experiencing these factors impacts treatment outcomes.

METHOD

We conducted a retrospective chart review of young adults admitted to a PHP with AN (n = 95) and atypical AN (n = 59). Histories of psychiatric comorbidities and adverse childhood experiences were obtained from initial psychiatric evaluations. ED symptoms were assessed at intake and discharge with the Eating Disorder Examination-Questionnaire (EDE-Q).

RESULTS

No significant differences were found at intake in ED symptom severity or prevalence of lifetime trauma, childhood abuse, number of psychiatric diagnoses, or suicidal thoughts and behavior. Symptomatology at discharge also did not differ between groups. Emotional abuse was significantly related to discharge shape and weight overvaluation. No other intake characteristics were significantly related to discharge symptomatology.

DISCUSSION

To our knowledge, this is the first study to compare the prevalence of comorbidities for both AN and atypical AN, as well as differential treatment outcomes for these individuals in a PHP. Results add to growing literature suggesting that, other than weight, AN and atypical AN have few properties that reliably distinguish them from one another.

PUBLIC SIGNIFICANCE

This study adds to a growing body of literature that raises questions about whether anorexia nervosa (AN) and atypical AN are truly different diagnoses. Our findings suggest these two groups present to treatment in a partial hospitalization program (PHP) with similar ED symptoms, as well as prevalence of lifetime trauma, childhood abuse, suicidal thoughts and behavior, and number of psychiatric comorbidities, and demonstrate similar treatment trajectories in PHP.

Comparisons between atypical anorexia nervosa and anorexia nervosa: Psychological and comorbidity patterns

OBJECTIVE

Literature comparing "atypical" anorexia nervosa (atypical AN) and anorexia nervosa (AN) suggests these diagnoses share significant similarities in eating disorder (ED) pathology and psychiatric comorbidities. This study evaluated potential differences in ED pathology, psychiatric comorbidity, associated mechanisms (i.e., ED fears and perfectionism), and demographic factors (i.e., ethnicity and age) between individuals with atypical AN and AN.

METHOD

Data from seven protocols were combined for a total 464 individuals diagnosed with atypical AN (n = 215) or AN (n = 249). Between-group differences in ED severity and behaviors, psychiatric comorbidities, ED fears, perfectionism, and demographic factors were assessed using t-tests, Wilcoxon rank-sum tests, and Fisher's exact test.

RESULTS

Participants with atypical AN reported higher levels of overvaluation of weight and shape than those with AN. Participants with AN scored higher on food-related fears (anxiety about eating, food avoidance behaviors, and feared concerns) and fears of social eating, as well as obsessive-compulsive symptoms. Participants with AN were more likely to identify as Asian or Pacific Islander. No other statistically significant differences were found between groups for overall ED severity, ED behaviors, psychiatric comorbidities, general ED fears, perfectionism, or demographic factors.

DISCUSSION

Overall, results support previous literature indicating limited differences between individuals with atypical AN and AN, though individuals with atypical AN reported more overvaluation of weight and shape and those with AN reported higher food and social eating fears and obsessive-compulsive symptoms. Relatively few overall differences between atypical AN and AN highlight the importance of exploring dimensional conceptualizations of AN as an alternative to the current categorical conceptualization.

PUBLIC SIGNIFICANCE

This study assessed differences among individuals with atypical anorexia nervosa and anorexia nervosa in eating disorder severity and behaviors, comorbid psychiatric diagnoses, associated mechanisms, and demographic factors. Few differences emerged, though participants with atypical anorexia nervosa reported more overvaluation of weight and shape, while those with anorexia nervosa reported more food and social eating fears and higher obsessive-compulsive symptoms. Results support exploration of these diagnoses as a spectrum disorder.

Eating disorder psychopathology, psychiatric impairment, and symptom frequency of atypical anorexia nervosa versus anorexia nervosa: A systematic review and meta-analysis

OBJECTIVES

Restrictive eating disorders (EDs) occur across the weight spectrum, but historically more focus has been given to anorexia nervosa (AN) than atypical anorexia nervosa (atypAN). AtypAN's relegation to a diagnosis in the "other specified feeding and eating disorder" (OSFED) category and paucity of research surrounding atypAN invariably implies a less clinically severe ED. However, a growing body of research has begun to question the assumption that atypAN is less severe than AN. The current review and meta-analysis aimed to provide a comprehensive review to compare atypAN and AN on measures of eating disorder psychopathology, impairment, and symptom frequency to test whether atypAN is truly less clinically severe than AN.

METHODS

Twenty articles that reported on atypAN and AN for at least one of the variables of interest were retrieved from PsycInfo, PubMed, and ProQuest.

RESULTS

For eating-disorder psychopathology, results indicated that differences were nonsignificant for most indicators; however, atypAN was associated with significantly higher shape concern, weight concern, drive for thinness, body dissatisfaction, and overall eating-disorder psychopathology than AN. Results indicated that atypAN and AN did not significantly differ on clinical impairment or the frequency of inappropriate compensatory behaviors, whereas there was a significantly higher frequency of objective binge episodes in AN (vs. atypAN).

DISCUSSION

Overall, findings indicated that, in contrast to the current classification system, atypAN and AN were not clinically distinct. Results underscore the need for equal access to treatment and equal insurance coverage for restrictive EDs across the weight spectrum.

PUBLIC SIGNIFICANCE

The current meta-analysis found that atypAN was associated with higher drive for thinness, body dissatisfaction, shape concern, weight concern, and overall eating-disorder psychopathology than AN; whereas AN was associated with higher frequency of objective binge eating. Individuals with AN and atypAN did not differ on psychiatric impairment, quality-of-life, or frequency of compensatory behaviors, highlighting the need for equal access to care for restrictive EDs across the weight spectrum.

Differentiation between atypical anorexia nervosa and anorexia nervosa using machine learning

OBJECTIVE

Body mass index (BMI) is the primary criterion differentiating anorexia nervosa (AN) and atypical anorexia nervosa despite prior literature indicating few differences between disorders. Machine learning (ML) classification provides us an efficient means of accurately distinguishing between two meaningful classes given any number of features. The aim of the present study was to determine if ML algorithms can accurately distinguish AN and atypical AN given an ensemble of features excluding BMI, and if not, if the inclusion of BMI enables ML to accurately classify between the two.

METHODS

Using an aggregate sample from seven studies consisting of individuals with AN and atypical AN who completed baseline questionnaires (N = 448), we used logistic regression, decision tree, and random forest ML classification models each trained on two datasets, one containing demographic, eating disorder, and comorbid features without BMI, and one retaining all features and BMI.

RESULTS

Model performance for all algorithms trained with BMI as a feature was deemed acceptable (mean accuracy = 74.98%, mean area under the receiving operating characteristics curve [AUC] = 74.75%), whereas model performance diminished without BMI (mean accuracy = 59.37%, mean AUC = 59.98%).

DISCUSSION

Model performance was acceptable, but not strong, if BMI was included as a feature; no other features meaningfully improved classification. When BMI was excluded, ML algorithms performed poorly at classifying cases of AN and atypical AN when considering other demographic and clinical characteristics. Results suggest a reconceptualization of atypical AN should be considered.

PUBLIC SIGNIFICANCE

There is a growing debate about the differences between anorexia nervosa and atypical anorexia nervosa as their diagnostic differentiation relies on BMI despite being similar otherwise. We aimed to see if machine learning could distinguish between the two disorders and found accurate classification only if BMI was used as a feature. This finding calls into question the need to differentiate between the two disorders.

Feasibility and preliminary effectiveness of a cognitive-behavioral, family-centered partial hospitalization program for adolescents with anorexia nervosa and atypical anorexia nervosa at six- and twelve-month follow-up

This study examined the feasibility and preliminary effectiveness of a cognitive-behavioral, family-centered partial hospitalization program (PHP) for adolescents with anorexia nervosa (AN) and atypical AN (AAN), and described the outpatient services received following discharge. Participants (N = 31) completed anthropometric and self-report assessments at admission, discharge, and six and twelve months after discharge from the PHP. Descriptive statistics explored markers of feasibility. Paired samples t-tests evaluated changes in weight and eating disorder (ED) symptomatology from admission to discharge, admission to six-month follow-up, and admission to twelve-month follow-up. Descriptive statistics and effect sizes compared symptoms at each timepoint between participants with AN and AAN. Results indicated that we were successful at recruiting greater than 50% of adolescents approached for this study. We collected follow-up data from more than 70% of participants at discharge, but did not meet this retention benchmark at six-month and twelve-month follow-ups. The entire sample demonstrated significant improvements in weight and ED symptomatology from admission to discharge, and generally maintained these improvements at six- and twelve-month follow-up. While descriptive statistics suggested that participants with AN and AAN received similar outpatient services following discharge from the PHP, those with AN experienced greater improvement in self-reported ED symptomatology than those with AAN at six- and twelve-month follow-up. These findings provide preliminary support for the efficacy of PHPs in treating adolescents with AN and AAN. Further research with larger sample sizes should investigate whether adolescents with AAN experience poorer outcomes than those with AN following discharge from a PHP.

Family-based treatment takes longer for adolescents with mental health comorbidities: findings from a community mental health service

Children and adolescents diagnosed with an eating disorder often meet the diagnosis of another mental health disorder. In addition to eating disorders, individuals with comorbid disorders have higher suicide rates and more severe and chronic eating disorder symptoms. The present research aimed to investigate the influence of comorbid conditions on the treatment outcomes of children and adolescents that attended a public community mental health service. It was hypothesised that the patients with comorbidities would have a more extended treatment duration, slower rates of weight restoration, more hospital admissions for medical compromise, and poorer functioning than those without comorbidities. Data from 78 past patients at the Eating Disorder Program in Queensland, Australia, were analysed. Patients with comorbidities demonstrated similar recovery rates to those without comorbidities. However, those with comorbid conditions had longer episodes of treatment. The study's results support using Family Based Treatment for patients with and without comorbidities. The implications of the findings for public mental health services and directions for future research are discussed.

An exploration of the association between premorbid weight status on patient and caregiver factors at pre and post-treatment among youth with anorexia nervosa/atypical anorexia nervosa

Patients with atypical anorexia nervosa (AAN) or anorexia nervosa (AN) with premorbid history of higher weight (PHW; median BMI ≥ 85th %ile) may report greater eating disorder (ED) pathology, anxiety, and depression, than patients with premorbid history of lower weight (PLW; mBMI <85th %ile). Less is known about caregiver attitudes or treatment outcome related to premorbid weight history. The current study examined associations between premorbid weight history and patient/caregiver factors at presentation, during treatment, and end of treatment among adolescents (N = 138) diagnosed with AN/AAN and their caregivers who received interdisciplinary ED treatment. The sample comprised adolescents with PHW (n = 58, 40.6 %) or PLW (n = 82, 59.4 %). Adolescents with PHW did not differ with regard to patient- or caregiver-reported ED symptoms, comorbid psychopathology, rates of treatment completion, and attainment of estimated body weight compared to PLW (ps > .05). Adolescents with PHW (vs. PLW) were more likely to be diagnosed with AAN (67.9 %, p < .001), identify as cisgender male (p < .001) and to have lost more weight prior to presentation (p < .001). Perceived caregiver burden was lower among adolescents with PHW vs. PLW (p < .001). Further research should expand on this preliminary study exploring associations between premorbid weight history on patient and caregiver factors at treatment presentation and conclusion to enhance the efficacy of evidence-based treatment across the weight-spectrum.

Atypical anorexia nervosa: Rethinking the association between target weight and rehospitalization

OBJECTIVE

Bodyweight restoration is one of the most important targets in adolescent inpatient treatment of anorexia nervosa (AN). This study examined the association between achieving target weight and rehospitalization in two groups of adolescents with AN and atypical anorexia nervosa (AAN) admitted to a specialized inpatient unit.

METHOD

Included were 202 adolescent patients hospitalized in a specialized eating disorder unit, 10-18 years old. One hundred fifty-four adolescents were diagnosed with AN, and 48 with AAN. We examined the patients' demographic and clinical characteristics, the achievement of treatment goals, and their rehospitalization history within a year of discharge from the unit.

RESULTS

Log-linear regression indicated a significant association between achieving target weight during the inpatient program and rehospitalization at one-year follow-up in the AN group; this association was not significant in the AAN group.

DISCUSSION

This study emphasizes the importance of differentiating patients with AAN from those with classical AN. Specifically, it raises questions about the predictive power of target weight at discharge in preventing relapse and its centrality in determining AAN patients' treatment plans.

Restrictive eating disorders in higher weight persons: A systematic review of atypical anorexia nervosa prevalence and consecutive admission literature

OBJECTIVE

Currently, there is debate in the eating disorders field regarding how to define atypical anorexia (AAN), how prevalent it is in community and clinical settings, and how AAN rates compare with low-weight AN. This systematic review assesses AAN literature from 2007 to 2020, to investigate: (a) the demographic characteristics of AAN studies, (b) the prevalence of AAN compared with AN, (c) the range of operational definitions of AAN and the implications of these definitions, and (d) the proportion of patients with AAN and AN represented in consecutive admission and referral samples.

METHOD

PsychINFO, CINAHL, PubMed, Greylit.org, and ProQuest databases were searched according to methods for Preferred Reporting Items for Systematic Reviews and Meta-Analyses systematic reviews, yielding 3,184 potential articles. Seventy-five eligible studies were coded for sixty-one variables.

RESULTS

Clinical samples predominantly included younger, female, white samples with limited diversity. In epidemiological designs, AAN was typically as common or more common than AN, and AAN rates varied significantly based on the population studied and operational definitions. In consecutive clinical samples, AAN was frequently less represented.

DISCUSSION

Although AAN appears to occur more frequently than AN in communities, fewer patients with AAN are being referred and admitted to eating disorder specific care, particularly in the United States. Given the significant medical and psychosocial consequences of AAN, and the importance of early intervention, this represents a crucial treatment gap. Additionally, results suggest the need for fine-tuning diagnostic definitions, greater diversity in AAN studies, and increased screening and referral for this vulnerable population.

Identifying research priorities for the study of atypical anorexia nervosa: A Delphi study

OBJECTIVE

Individuals meeting all criteria for anorexia nervosa (AN) except that weight falls within or above the normal range despite significant weight loss are categorized as having atypical AN (AAN). Existing research has provided mixed evidence concerning the diagnostic demarcation of AN and AAN. The aim of the present study was to identify research priorities for furthering the understanding of AN and AAN as diagnostic entities.

METHOD

Employing the Delphi methodology, experts in the field were invited to suggest research questions that need to be explored in the demarcation of AN from AAN. This yielded 24 research areas, that were presented in subsequent rounds where panelists were asked to prioritize areas of primary interest.

RESULTS

Fifty-three panelists completed all three Delphi rounds. Consensus was only reached on three items considered to be of primary interest: medical, neurobiological, and neurological factors; epidemiology and natural course; and treatment response in AAN compared to AN. In contrast, questions of premorbid weight and determining the need for and nature of a body mass index cutoff differentiating between AAN and AN were seen as being of low priority.

DISCUSSION

These findings reveal a relatively low degree of consensus on the demarcation of AN from AAN in the field of eating disorders. A reason could be that the definition and use of the AAN category vary in research and clinical practice. In order to achieve further diagnostic clarity, research on the demarcation of AAN and AN should focus on the identified prioritized research areas.

Tackling mixed messages: Practitioner reflections on working with adolescents with atypical anorexia and their families

The treatment of atypical anorexia nervosa (AN) poses new research and practice challenges for the field of eating disorders. The objective of this study was to describe frontline practitioners' perceptions of differences between adolescents living with atypical versus typical AN, as well as the intervention challenges they experience when working with these adolescents and their families. We followed the principles of fundamental qualitative description and recruited a purposeful sample of practitioners treating adolescent eating disorders to complete a one-on-one semi-structured interview. Conventional content analysis and the constant comparison technique were used for data analysis. A total of 23 practitioners from four countries participated in this study. Practitioners described that adolescents with atypical AN present with higher pre-morbid weights and rates of weight-based teasing compared to their AN peers. Clinical challenges perceived by practitioners to be specific to working with adolescents with atypical AN included: addressing conflicting messages about eating disorders and weight loss, empathizing with a justified fear of weight gain, and increased risk for parental and therapist collusion with the eating disorder. Findings have implications for delivering interventions to adolescents seeking care for atypical AN.

Obsessions are strongly related to eating disorder symptoms in anorexia nervosa and atypical anorexia nervosa

Anorexia nervosa (AN) and obsessive-compulsive disorder (OCD) are highly comorbid. However, little research has examined which specific cognitive-behavioral aspects (e.g., checking, obsessing) of OCD are most relevant in those with AN. Furthermore, there is no research examining aspects of OCD in Atypical AN. The current two studies (N = 139 and N = 115 individuals diagnosed with AN/Atypical AN) examined a) which aspects of OCD were most related to AN symptomatology and b) if there were differences in OCD between individuals diagnosed with AN vs Atypical AN. We found that obsessing was most related to AN symptoms. We also found that there were no substantial significant differences between AN and Atypical AN. These findings add to the literature suggesting minimal differences between AN and Atypical AN, specifically regarding OCD symptomatology. These findings clarify that obsessions (rather than compulsions) may be the specific aspect of OCD most warranting treatment intervention in AN and Atypical AN.

Adolescents with full or subthreshold anorexia nervosa in a naturalistic sample - characteristics and treatment outcome

BACKGROUND

Anorexia Nervosa (AN) destroys developmentally important early years of many young people and knowledge is insufficient regarding course, treatment outcome and prognosis. Only a few naturalistic studies have been conducted within the field of eating disorder (ED) research. In this naturalistic study we included adolescents with AN or subthreshold AN treated in outpatient care, and the overall aim was to examine sample characteristics and treatment outcome. Additional aims were to examine potential factors associated with remission as an outcome variable, and possible differences between three time periods for treatment onset.

METHODS

Participants were identified through the Swedish national quality register for eating disorder treatment (SwEat), in which patients are registered at treatment onset and followed up once a year until end of treatment (EOT). Inclusion criteria were: medical or self-referral to one of the participating treatment units between 1999 and 2014, 13-19 years of age at initial entry into SwEat and diagnosed with AN or subthreshold AN. The total sample consisted of 3997 patient from 83 different treatment units.

RESULTS

The results show that 55% of the participants were in remission and approximately 85% were within a healthy weight range at EOT. Of those who ended treatment according to plan, 70% were in remission and 90% within a healthy weight range. The average treatment duration was approximately 15 months. About one third of the patients terminated treatment prematurely, which was associated with a decreased chance of achieving remission. Remission rates and weight recovery increased over time, while treatment duration decreased. Considering treatment outcome, the results did not show any differences between patients with AN or subthreshold AN.

CONCLUSIONS

The present study shows a relatively good prognosis for adolescent patients with AN or subthreshold AN in routine care and the results indicate that treatment for adolescents with ED in Sweden has become more effective over the past 15 years. The results of the present study contribute to the scope of treatment research and the large-scale naturalistic setting secures the generalizability to a clinical environment. However, more research is needed into different forms of evidence, new research strategies and diversity of treatment approaches.

TRIAL REGISTRATION

Registered in FOU in Sweden (Researchweb.org) 2014-04-14, ID nr 147301.

VIDEOFLUOROSCOPIC EVALUATION OF SWALLOWS IN ANOREXIA NERVOSA

BACKGROUND

There are some studies in the literature about the feeding behavior and masticatory process in patients with feeding disorders; however, it is not very well known if there are alterations in oral-pharyngeal swallowing dynamics in subjects with anorexia nervosa.

OBJECTIVE

To evaluate the oral and pharyngeal bolus transit in patients with anorexia nervosa.

METHODS

The study was conducted with 8 individuals clinically diagnosed and in treatment for restricting-type anorexia nervosa (seven women and one man), and 14 healthy individuals with no digestive or neurological symptoms (10 women, 4 men). Swallows were evaluated by videofluoroscopy with three swallows of 5 mL liquid bolus and three swallows of 5 mL paste bolus consistency, given in a random sequence. The participants were asked after each swallow about the sensation of the bolus passage.

RESULTS

In the analysis of oral-pharyngeal transit duration, the mean duration of pharyngeal transit with paste bolus in patients with anorexia was shorter than in healthy volunteers (P=0.02). In the duration of movement of the hyoid bone, longer movement was observed in anorexia than in healthy volunteers with liquid bolus (P=0.01). With liquid bolus, five (62.5%) patients and one (7.1%) control had sensation of the bolus passage (P<0.05).

CONCLUSION

There seems to be no important alterations of swallowing in subjects with anorexia nervosa, although the results suggest that pharyngeal transit has shorter duration than that seen in healthy volunteers and the hyoid movement duration is longer in patients than in healthy volunteers. Fast pharyngeal transit may be the cause of bolus transit perception in patients with anorexia nervosa.

Epidemiology of eating disorders in Europe: prevalence, incidence, comorbidity, course, consequences, and risk factors

PURPOSE OF REVIEW

Eating disorders - anorexia nervosa, bulimia nervosa, and binge eating disorder - affect numerous Europeans. This narrative review summarizes European studies on their prevalence, incidence, comorbidity, course, consequences, and risk factors published in 2015 and the first half of 2016.

RECENT FINDINGS

Anorexia nervosa is reported by <1-4%, bulimia nervosa <1-2%, binge eating disorder <1-4%, and subthreshold eating disorders by 2-3% of women in Europe. Of men, 0.3-0.7% report eating disorders. Incidences of anorexia appear stable, whereas bulimia may be declining. Although the numbers of individuals receiving treatment have increased, only about one-third is detected by healthcare. Over 70% of individuals with eating disorders report comorbid disorders: anxiety disorders (>50%), mood disorders (>40%), self-harm (>20%), and substance use (>10%) are common. The long-term course of anorexia nervosa is favorable for most, but a substantial minority of eating disorder patients experience longstanding symptoms and somatic problems. The risk of suicide is elevated. Parental psychiatric disorders, prenatal maternal stress, various family factors, childhood overweight, and body dissatisfaction in adolescence increase the risk of eating disorders.

SUMMARY

Eating disorders are relatively common disorders that are often overlooked, although they are associated with high comorbidity and serious health consequences.

The DSM-5 diagnostic criteria for anorexia nervosa may change its population prevalence and prognostic value

The definition of anorexia nervosa was revised for the Fifth Edition of the Diagnostic and Statistical Manual (DSM-5). We examined the impact of these changes on the prevalence and prognosis of anorexia nervosa. In a nationwide longitudinal study of Finnish twins born 1975-1979, the women (N = 2825) underwent a 2-stage screening for eating disorders at mean age 24. Fifty-five women fulfilled DSM-IV criteria for lifetime anorexia nervosa. When we recoded the interviews using DSM-5 criteria, we detected 37 new cases. We contrasted new DSM-5 vs. DSM-IV cases to assess their clinical characteristics and prognosis. We also estimated lifetime prevalences and incidences and tested the association of minimum BMI with prognosis. We observed a 60% increase in the lifetime prevalence of anorexia nervosa using the new diagnostic boundaries, from 2.2% to 3.6%. The new cases had a later age of onset (18.8 y vs. 16.5, p = 0.002), higher minimum BMI (16.9 vs. 15.5 kg/m(2), p = 0.0004), a shorter duration of illness (one year vs. three years, p = 0.002), and a higher 5-year probability or recovery (81% vs. 67%, p = 0.002). Minimum BMI was not associated with prognosis. It therefore appears that the substantial increase in prevalence of anorexia nervosa is offset by a more benign course of illness in new cases. Increased diagnostic heterogeneity underscores the need for reliable indicators of disease severity. Our findings indicate that BMI may not be an ideal severity marker, but should be complemented by prognostically informative criteria. Future studies should focus on identifying such factors in prospective settings.