Evaluating ICD-11 anorexia nervosa in a clinical youth sample: a comparison with ICD-10

Objective: The International Classification of Diseases (ICD) was recently updated to an 11th edition, introducing significant changes to the diagnostic criteria for Anorexia Nervosa (AN). Little is known about how these updated criteria impact diagnostic classification in previously diagnosed populations. This study aims to examine how a Danish youth sample previously diagnosed with ICD-10 AN or Atypical AN (atypAN) would classify under ICD-11 criteria, including the application of the new subtype specifier. Furthermore, it investigates how ICD-11 diagnoses and subtypes relate to ED symptom severity compared to ICD-10 diagnoses. Methods: a prior ICD-10 AN and atypAN sample (N = 895) was reclassified under ICD-11 criteria, categorising those not meeting AN criteria as OSFED. AN cases were subtyped into Restrictive (AN-R) or Binge-Purge (AN-BP). Multiple linear models examined associations between 1) ICD-10 diagnoses; 2) ICD-11 diagnoses; and 3) AN subtypes, and EDE scores, while controlling for age and sex. Results: ICD-11 reclassification led to all ICD-10 AN and 127 atypAN cases meeting AN criteria. Only ICD-11 diagnosis was significantly associated with ED symptom severity, with AN showing greater severity than OSFED. AN-BP exhibited greater severity than AN-R. Discussion: ICD-11 increased number of full-threshold diagnoses and may thus aid in providing adequate treatment, and findings supported the subtyping introduced in ICD-11. However, a substantial amount of prior atypAN cases were not captured in ICD-11 diagnostic criteria. All prior ICD-10 AN cases met ICD-11 AN criteria, while 127 of 411 prior atypAN cases were reclassified as AN, with the remainder categorized as OSFED. Only ICD-11 AN diagnosis, not ICD-10 diagnosis, was significantly associated with greater ED symptom severity. The AN-Binge-Purge subtype exhibited higher levels of ED symptoms than the AN-Restrictive subtype, supporting the subtyping system.