Atypical Anorexia Nervosa May Not Be Clinically Distinct

Extremely low body weight is the primary diagnostic criterion that distinguishes anorexia nervosa (AN) from other restrictive eating disorders. However, many patients present with all the hallmarks of AN, including restrictive eating, fear of weight gain, and extreme weight loss, yet still have a BMI within the “healthy” range, a condition called atypical anorexia nervosa (atypAN).¹

Atypical Anorexia Nervosa

The term “atypical anorexia nervosa” was coined in 1973, and in 2013 was added to the fifth edition of the American Psychiatric Association’s DSM (DSM-5).¹ However, this variant of AN has not been well studied, and the lack of research may have given the impression that atypAN is less severe than the more common AN.²

“There have been questions for some time about whether or not weight should be a defining criterion for eating disorder and whether or not it should apply to something like anorexia,” said Cynthia Ann Flynn, PhD, clinical assistant professor and director of the eating disorders recovery program in the department of psychiatry and behavioral medicine at Seattle Children's Hospital. “People can have eating disorders at any size and weight, so our diagnostic categories have made it sometimes difficult to diagnose.”

In addition, there has long been an assumption that the atypical form of the disease was less severe.^1,2

Determining Clinical Severity of Anorexia Subtype

Kelsie T. Forbush, PhD, led a team of researchers at the University of Kansas in a literature review and meta-analysis to determine whether atypical AN is indeed clinically less severe than AN. Their findings were published in June 2023 in International Journal of Eating Disorders.²

Study Methods

Dr. Forbush and team searched APA PsycInfo, PubMed, and ProQuest using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. In selecting studies for inclusion, they used the DSM-5 definition of atypAN.² Inclusion in the atypAN group required that authors of a study specified the diagnostic criteria they used, such as whether it was BMI range, percent weight loss, or other criteria. The authors also had to state what DSM or ICD criteria they used. Gray literature was included in the analysis to prevent potential-for-publication bias from influencing study findings.

The researchers did not include sub-threshold AN presentations in the meta-analysis but did consider presentations with low weight but no fear of gaining weight or of becoming fat; low weight without amenorrhea if using DSM-IV criteria; or AN presentations with BMIs of 18.5 to 19.0 as sub-threshold AN.

Eating disorder psychopathology was measured using the Eating Disorder Examination-Questionnaire (EDE-Q), EDE subscales, and Eating Disorder Inventory subscales. Impairment due to eating disorder and global impairment were also assessed. Symptom frequency measurements looked at frequency of objective binge episodes; subjective binge episodes; self-induced vomiting; laxative misuse; diuretic misuse; excessive, compulsive, or compensatory exercise; and fasting or food restriction.

The final analysis included 20 articles.

Atypical and Typical Anorexia May Not Be Clinically Distinct

For most indicators, Dr. Forbush’s analysis found no significant differences between anorexia nervosa and atypAN. The findings suggest that atypAN and AN are not clinically distinct and that atypAN may not require extremely low BMI compared to anorexia nervosa to be diagnosed. However, the team did find some differences.

As compared to AN, atypAN was associated with a higher drive for thinness, more body dissatisfaction, more concern over weight and body shape, and more overall eating disorder psychopathology. Anorexia nervosa, on the other hand, was associated with a 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.

Reshaping Category Labels

“Diagnostic labels carry great importance; diagnoses are necessary to ensure adequate insurance coverage, inform treatment planning, and facilitate communication between providers,” Dr. Forbush’s team wrote. “It is, therefore, essential to ensure that diagnostic labels are empirically supported.”²

Dr. Flynn agreed that the review sheds much-needed light on the issue of diagnostic categories. However, she added that, even more importantly, these findings suggest that people who present with atypical anorexia nervosa are in no less psychological pain than those with AN, providing support for the observation that you can have an eating disorder at any weight.

“If someone is struggling with their relationship with food or struggling with psychological pain around their weight or shape or how they're eating, treatment really can help,” Dr. Fynn said. “We never want people to think that their weight is too high to be deserving of help.”