For adolescents, DSM-5 differentiates anorexia nervosa (AN) and atypical AN with the 5th BMI-centile-for-age. We hypothesized that the diagnostic weight cut-off yields (i) lower weight loss in atypical AN and (ii) discrepant premorbid BMI distributions between the two disorders. Prior studies demonstrate that premorbid BMI predicts admission BMI and weight loss in patients with AN. We explore these relationships in atypical AN. Based on admission BMI-centile < or ≥5th, participants included 411 female adolescent inpatients with AN and 49 with atypical AN from our registry study. Regression analysis and t-tests statistically addressed our hypotheses and exploratory correlation analyses compared interrelationships between weight loss, admission BMI, and premorbid BMI in both disorders. Weight loss in atypical AN was 5.6 kg lower than in AN upon adjustment for admission age, admission height, premorbid weight and duration of illness. Premorbid BMI-standard deviation scores differed by almost one between both disorders. Premorbid BMI and weight loss were strongly correlated in both AN and atypical AN. Whereas the weight cut-off induces discrepancies in premorbid weight and adjusted weight loss, AN and atypical AN overall share strong weight-specific interrelationships that merit etiological consideration. Epidemiological and genetic associations between AN and low body weight may reflect a skewed premorbid BMI distribution. In combination with prior findings for similar psychological and medical characteristics in AN and atypical AN, our findings support a homogenous illness conceptualization. We propose that diagnostic subcategorization based on premorbid BMI, rather than admission BMI, may improve clinical validity. Because body weights of patients with AN must drop below the 5th BMI-centile per DSM-5, they will inherently require greater weight loss than their counterparts with atypical AN of the same sex, age, height and premorbid weight. Indeed, patients with atypical AN had a 5.6 kg lower weight loss after controlling for these variables. In comparison to the reference population, we found a lower and higher mean premorbid weight in patients with AN and atypical AN, respectively. Considering previous psychological and medical comparisons showing little differences between AN and atypical AN, we view a single disorder as the most parsimonious explanation. Etiological models need to particularly account for the strong relationship between weight loss and premorbid body weight.

In this special issue, international researchers investigate how atypical anorexia nervosa (atypical AN) differs from anorexia nervosa (AN) and other eating disorders with respect to demographics, psychological and physiological morbidity, as well as treatment course and outcome. Manuscripts in this special issue report that atypical AN is associated with substantial medical and psychological morbidity, and the majority of studies find few differences between atypical AN and AN. While much remains to be learned about the long-term course and treatment response of individuals with atypical AN to psychological and pharmacological interventions, the evidence supports conceptualization of atypical AN as part of a spectrum-based restrictive eating disorder. These findings together with the potentially stigmatizing use of the term "atypical" suggest it may be time to revise the existing definition of atypical AN.

In their systematic review on parent illness representations in their children with anorexia nervosa (AN), Marchetti and Sawrikar (International Journal of Eating Disorders, 2023) integrate past research on the parental experience of the illness, investigating whether the Common Sense Model of Self-Regulation (CSM) is a useful framework for understanding parental responses to AN. Given that family-based treatment (FBT) is a first-line treatment for adolescents with eating disorders and is based upon integrating parents into the treatment process, it is especially relevant to explore how parent illness representations may impact FBT. In this commentary, we describe how FBT is designed to support parents and address many of the common unhelpful beliefs and emotions associated with parenting an adolescent with AN. We include specific examples of how parents can be supported within FBT as manualized. We also examine parental representations that may not be addressed by FBT, and how these may impact treatment outcomes in FBT, possibly via the impact of expressed emotion. Future research is needed to determine if modifications to FBT are required to address parental representations of the illness. We end by expanding upon Marchetti and Sawrikar's suggestions on how treatment could be extended to better support parents as necessary.

To examine trajectories of therapeutic skills use and weekly relations between skills use and symptom change during the enhanced version of cognitive-behavioral therapy (CBT-E) for bulimia nervosa (BN). Fifty-five adults (M age: 39.0 ± 14.1; 83.9% female; 64.3% White, 93.6% non-Hispanic/Latino) receiving CBT-E for BN-spectrum eating disorders (EDs) self-monitored their use of five therapeutic skills (i.e., regular eating, eating enough to prevent excessive hunger and eating a range of macronutrients, breaking dietary rules, urge management strategies, and mood management strategies) several times per day during treatment. Patients also self-reported their ED symptoms (i.e., frequency of binge eating, compensatory behaviors, and dietary restraint) weekly. We examined trajectories of use of each CBT-E skill and temporal relations between skills use and ED symptoms from week-to-week during treatment. Participants showed significant increases in eating enough to prevent excessive hunger and eating a range of macronutrients from week-to-week (p < .05). Regular eating, eating enough to prevent excessive hunger, and eating a range of macronutrients 1 week predicted lower binge eating and compensatory behaviors the same week and the following week, and urge management strategy use predicted greater binge eating the same week and the following week (p < .05). Results showed temporal relationships between therapeutic skills use and symptom change on a weekly level, with evidence that using skills targeting dietary restraint was associated with lower BN symptoms. Findings highlight the promise of future work to elucidate the most potent CBT-E skills for symptom improvement and inform more targeted interventions. Findings showed weekly relationships between therapeutic skills use and symptom change during treatment, with evidence that using CBT-E skills aimed to reduce dietary restraint (i.e., regular eating, eating enough to prevent excessive hunger, and eating a range of macronutrients) was associated with lower BN symptoms. Future work has the potential to identify the most potent CBT-E skills for symptom improvement and inform more targeted interventions.