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

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Highlights

  • The lifetime prevalence of anorexia nervosa increased by 60% using the new DSM-5 definition.

  • The new DSM-5 cases had a later age of onset, higher minimum BMI, and a shorter duration of illness that DSM-IV cases.

  • Minimum body mass index was not associated with likelihood of recovery.

Abstract

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/m2, 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.

Introduction

Anorexia nervosa is a serious and potentially fatal illness (Walsh 2013). The definition of anorexia nervosa was recently revised for the DSM-5 (American Psychiatric Association 2013). One of the leading reasons for the revision was to reduce the number of patients who receive the diagnosis eating disorder not otherwise specified (EDNOS), who constituted up to 60% of patients in specialized eating disorder units (Fairburn and Bohn, 2005, Zimmerman et al., 2008).

DSM-5 introduced three changes to the criteria defining anorexia nervosa: the weight loss criterion was revised, fear of weight gain does not need to be verbalized if behaviors interfering with weight gain can be observed, and amenorrhea was no longer required (American Psychiatric Association, 2013, Attia et al., 2013). These diagnostic changes were supported by a number of studies that found few differences in demographics, eating disorder pathology, and psychiatric comorbidity between patients who meet strict diagnostic criteria for anorexia nervosa and their subthreshold counterparts (Eddy et al., 2008, Helverskov et al., 2011, Thomas et al., 2009).

Another new feature in the DSM-5 is the introduction of a body mass index (BMI) based severity rating. Previous research has shown that BMI-based severity is associated with disorder detection and access to treatment, but not with recovery rates (Smink et al., 2014).

A consensus reigns that the recent diagnostic changes in the DSM will increase the proportion of patients with anorexia nervosa and decrease the number of residual diagnoses (Machado et al., 2013, Ornstein et al., 2013, Keel et al., 2011, Nakai et al., 2013, Birgegard et al., 2012). Among community-based adolescents, the prevalence of anorexia nervosa increased by 50% (Smink et al., 2014). However, the impact of the changes has not been quantified in adult women. Furthermore, no previous studies have assessed the prognostic value of the diagnostic changes. Finally, there is little empirical evidence to substantiate the BMI-based severity assessment in anorexia nervosa. To address these questions, we conducted a nationwide population-based study to quantify the impact of recent changes in diagnostic criteria on the prevalence, incidence rate and prognosis of anorexia nervosa. We also examined the prognostic value of the BMI-based severity rating.

Section snippets

FinnTwin16 birth cohorts

This nationwide longitudinal cohort study of health behaviors in twins and their families (Kaprio et al., 2002) identified twin births in 1975–79 from the central population register of Finland. The FinnTwin16 cohort was restricted to those pairs who both were alive at age 16 and resident in Finland. Data collection and analysis were carried out in accordance with the latest version of the Declaration of Helsinki and approved by the ethics committee of the Department of Public Health of

Prevalence and incidence

We found 92 individuals with lifetime DSM-5 anorexia nervosa. Of these, 55 fulfilled DSM-IV criteria for anorexia nervosa (Keski-Rahkonen et al., 2007) whereas 37 were new DSM-5 cases. The inclusion of new DSM-5 cases increased the lifetime prevalence from 2.2% (95% CI 1.6–2.7%) to 3.6% (2.7–4.2%). The 15-year incidence rate (computed for the age interval 10–24 years) of anorexia nervosa increased from 140 (95% CI 110–180) to 230 (95% CI 180–280) per 100 000 person-years.

As a post hoc analysis,

Discussion

The revised DSM-5 diagnostic criteria for anorexia nervosa increased its population prevalence by 60% among community-based young adult women. This dramatic change means that the new DSM-5 classification may successfully address a previously unmet need. However, changes in diagnostic definitions may also increase phenotypical heterogeneity of anorexia nervosa. In our setting, the new DSM-5 cases of anorexia nervosa differed in some key respects from DSM-IV cases: the new cases had a later age

Conclusion

Applying the DSM-5 diagnostic criteria for anorexia nervosa to a community sample increased its lifetime prevalence substantially, by more than a half. The increase in occurrence was in some part offset by the more favorable prognosis of the new DSM-5 cases. Future prospective studies should further evaluate the role of this distinction and other factors that help to establish the severity of the disorder.

Funding

None of the funding sources had any involvement in study design, data collection or analysis, manuscript preparation, or decision to submit the article for publication.

Contributors

L. Mustelin and A. Keski-Rahkonen designed the study, reviewed literature, conducted the statistical analysis, and wrote the first draft of the manuscript; Y. Silén participated in reviewing the literature. A. Keski-Rahkonen and A. Raevuori led the DSM-5 diagnostic recoding; L. Mustelin and Y. Silén participated. A. Keski-Rahkonen and A. Raevuori conducted part of the clinical interviews and A. Keski-Rahkonen supervised the interviewers. J. Kaprio supervised the twin cohort data collection.

Conflict of interest

None of the authors declare any conflict of interest.

Acknowledgement

The data collection and analysis was supported by the Academy of Finland (grants 141054, 265240, 263278 and 264146 to JK and grant 259764 to AR). LM was supported by the Finnish Medical Foundation, the Yrjö Jahnsson Foundation, and the Medical Society of Finland (Finska Läkaresällskapet). YS was supported by the Children's Castle Foundation (Lastenlinnan säätiö) and the Psychiatric Research Foundation (Psykiatrian tutkimussäätiö) and Fund of Yrjö and Tuulikki Ilvonen.

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