Unveiling Severity Indicators for Anorexia and Bulimia Nervosa Treatment Success: DSM-5 Versus ICD-11 Versus Drive for Thinness

This study aimed to compare treatment outcomes associated with three severity indicators-DSM-5 for anorexia nervosa (AN) and bulimia nervosa (BN), ICD-11 for AN, and drive for thinness (DT) for AN and BN-within a treatment-seeking population. A total of 628 female participants diagnosed with either AN (n = 266; mean age = 26.71) or BN (n = 362; mean age = 29.49) were recruited from an ED unit. Upon admission, participants were classified based on DSM-5 (AN and BN) and ICD-11 severity categories. They underwent CBT-E comprehensive manualised programs, according to ED subtype, and were categorised into 'full remission', 'partial remission', 'non-remission' or 'drop-out' based on DSM-5 diagnostic criteria at discharge. Significant associations were found only for ICD-11 AN severity groups (p = 0.03, Cramer's V = 0.18), with 'dangerously low BMI' associated with poorer outcomes than 'significantly low BMI'. No other significant relationships were found with DSM-5 or DT severity groups. This study reveals the limitation of using a single severity indicator and emphasises the necessity of a comprehensive assessment to capture the complexities of AN and BN. Future research should also evaluate the validity of these severity measures across various factors, including biological correlates and psychopathology.