Response to the best available treatment for bulimia nervosa and binge-eating disorder is disease severity-dependent

To the Editor

Cognitive-behavioural therapy (CBT) is depicted in specialized literature as the best available treatment for both bulimia nervosa (BN) and binge-eating disorder (BED) and was given the highest rating in the National Institute of Mental Health review of evidence-based treatments. Nevertheless, it is well known that, even in studies with the best outcomes, a substantial proportion of treatment completers does not have remission of binge-eating (BE) and/or inappropriate weight compensatory behaviours (IWCBs), and the elucidation of factors accounting for heterogeneous and differential treatment response is crucial.

The (most recent) Fifth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) introduced disorder-specific severity ratings (ranging from mild to extreme) for BED and BN (American Psychiatric Association [APA], 2013), whose validity and clinical utility have recently been established, to inform clinicians and patients about disease severity and allow severity fluctuation and treatment progress to be tracked (Dakanalis et al., 2016, 2017). Specifically, four BED severity groups based on the weekly frequency of BE episodes and four BN severity groups based on the weekly frequency of episodes of IWCBs (e.g. self-induced vomiting, diuretic misuse, fasting, laxative misuse, and excessive exercise) were defined in the DSM-5 (APA, 2013) as follows: mild (1–3 episodes/week), moderate (4–7 episodes/week), severe (8–13 episodes/week), and extreme (>14 episodes/week). As mentioned, a substantial proportion of BED and BN patients do not have full and lasting response to (therapist-led) CBT. However, this picture represents only a general tendency if further refined by recent empirical evidence that contributes to gaining insight into the heterogeneous and severity-dependent response to CBT. Specifically, significant differences were found in remission of BE achieved by 6.7%, 38.7%, 66.7% and 98.5% of adult outpatients classified (at pre-treatment) with DSM-5 extreme, severe, moderate and mild severity of BED (Dakanalis et al., 2017). Likewise, significant differences were detected in remission of IWCBs achieved by 0%, 10.6%, 36.1% and 79.6% of adult outpatients classified (at pre-treatment) with DSM-5 extreme, severe, moderate and mild severity of BN (Dakanalis et al., 2016). An important query arising from these preliminary data highlighting the impact of the (DSM-5) severity of BED and BN on treatment outcome and requiring consideration in future treatment research, is whether pharmacological and psychological interventions should be combined to promote more appropriate treatment for moderate-to-extreme severity of BED and/or BN since this should differ from treatment regimens for mild severe presentations (Dakanalis et al., 2016, 2017).