(PS6-A16) Just What, Exactly, Is Atypical Anorexia? A Comparison of Clinical Characteristics Across Bulimia Nervosa and Atypical Anorexia in a Residential Treatment Sample

Introduction: Atypical anorexia nervosa (AAN) describes individuals who meet all of the criteria for anorexia nervosa, but despite significant weight loss, have a BMI within or above the normal range. There is debate surrounding whether AAN is a variant of bulimia nervosa (BN), which is similarly characterized by higher BMI and weight suppression, or whether it more closely represents higher weight or prodromal anorexia nervosa. Research comparing clinical symptoms across AAN and BN is needed to better understand AAN as a diagnostic entity.

Method: Participants were 1155 female patients at a residential eating disorder treatment center who completed surveys at intake. One-way analysis of covariance tests assessed differences between individuals with AAN (n = 231) and BN (n = 924) on the Eating Disorder Examination Questionnaire (EDE-Q) and its subscales, eating disorder behaviors, BMI, and weight suppression, while controlling for eating disorder duration.

Results: There were significant differences between AAN and BN groups on EDE-Q Eating Concern, EDE-Q Restraint, binge eating, and BMI (all p < .001). Post-hoc tests found that individuals with BN had significantly higher Eating Concern, binge eating, and BMI, whereas individuals with AAN endorsed significantly higher Restraint. There were no significant differences in EDE-Q Global, Shape and Weight Concern, purging, exercise, laxative use, or weight suppression between AAN and BN.

Conclusion: Results suggest that AAN has unique psychological, behavioral, and physical characteristics that distinguish it from BN. In particular, individuals with BN have greater concerns about food and eating, and engage in more frequent binge eating, whereas individuals with AAN show greater restraint from food, suggesting a different underlying illness. Individuals with AAN also engage in the same level of weight loss behaviors as BN, despite their relative lack of binge eating. Individuals with AAN may have a lower biological set point than those with BN, given their lower BMIs despite similar levels of weight suppression. AAN may not be a variant of BN, but have a biological and clinical presentation that more closely resembles higher-weight or prodromal anorexia nervosa.