Evaluating the predictive validity of purging disorder by comparison to bulimia nervosa at long‐term follow‐up

Abstract

Objective The current study sought to examine the predictive validity of the purging disorder diagnosis at long‐term follow‐up by comparing naturalistic outcomes with bulimia nervosa. Method Women with purging disorder (N = 84) or bulimia nervosa (N = 133) who had completed comprehensive baseline assessments as part of one of three studies between 2000 and 2012 were sought for follow‐up assessment. Nearly all (94.5%) responded to recruitment materials and 150 (69% of sought sample; 83.3% non‐Hispanic white; 33.40 [7.63] years old) participated at an average of 10.59 (3.71) years follow‐up. Participants completed the Eating Disorder Examination, the Structured Clinical Interview for DSM‐IV, and a questionnaire battery. Diagnostic groups were compared on eating disorder (illness status, recovery status, and eating pathology) and related outcomes. Group differences in predictors of outcome were explored. Results There were no significant differences in eating disorder presence (p = .70), recovery status (p = .87), and level of eating pathology (p = .17) between diagnostic groups at follow‐up. Post hoc equivalence tests indicated group differences were smaller than a medium effect size (p's ≤ .005). Groups differed in diagnosis at follow‐up (p = .002); diagnostic stability was more likely than cross‐over to bulimia nervosa for women with baseline purging disorder (p = .004). Discussion Although purging disorder and bulimia nervosa do not differ in long‐term outcomes, the relative stability in clinical presentation suggests baseline group differences in clinical presentation may be useful in augmenting treatments for purging disorder. Public Significance Statement While purging disorder is classified as an “other specified” eating disorder, individuals who experience this disorder have comparable negative long‐term outcomes as those with bulimia nervosa. This highlights the importance of screening for and treating purging disorder as a full‐threshold eating disorder.

Examining negative urgency as a predictor of eating disorder maintenance in purging syndromes

“…Sixty-eight women who engaged in recurrent self-induced vomiting (36 BN; 32 PD) completed diagnostic interviews and a questionnaire battery at baseline (Davis et al, 2020;Keel, Eckel, et al, 2018Keel et al, 2023) and were invited to participate in a larger follow-up study (Forney et al, 2021(Forney et al, , 2022.…”

“…The baseline parent study required a body mass index (BMI) between 18 and 26.5 kg/m 2 , recurrent self-induced vomiting (on average at least once weekly), and meeting criteria for DSM-5 BN or research criteria for PD. Our sample size is discrepant from Davis et al (2020) due to inclusion/exclusion criteria for the follow-up study (Forney et al, 2021(Forney et al, , 2022. While the baseline parent study (Davis et al, 2020;Keel, Eckel, et al, 2018;Keel et al, 2023) excluded those prescribed psychotropic medications, medical conditions, or treatments that affect appetite or weight, pregnancy or lactation, current major depressive disorder or current DSM-IV substance use disorder, the follow-up study (Forney et al, 2021(Forney et al, , 2022 included individuals who completed the baseline assessment and met criteria for BN or PD regardless of meeting other eligibility criteria (e.g., someone ineligible for the baseline parent study based on a high BMI would still be eligible for the follow-up study).…”

“…The Eating Disorder Examination (EDE; Cooper & Fairburn, 1987) was administered at baseline and follow-up to determine the presence of an eating disorder, assess recovery status at follow-up, and measure global baseline and follow-up eating pathology, consistent with prior work using this sample (Forney et al, 2021(Forney et al, , 2022. DSM-5 eating disorder diagnoses (e.g., anorexia nervosa, bulimia nervosa, binge-eating disorder, and other specified feeding or eating disorder) were used at follow-up.…”

“…Consistent with prior work using this sample (Forney et al, 2021(Forney et al, , 2022 were multiply imputed 40 times using the R package mice 3.4.0 (Van Buuren et al, 2011). As a missing data approach, multiple imputation is advantageous over other missing data methods, such as expectation maximization or listwise deletion, as pooling across multiple datasets allows for the modeling of sampling error and minimizes bias due to attrition (Enders, 2010).…”

“…Given the positive relationship between negative urgency and eating pathology (Cyders & Smith, 2008; Davis et al, 2020; Forney et al, 2014, 2016), we hypothesized that greater baseline negative urgency in individuals diagnosed with BN or PD would be associated with greater likelihood of an eating disorder diagnosis at 6‐year follow‐up, a reduced likelihood of recovery, and greater global eating pathology at 6‐year follow‐up. In the parent studies (Forney et al, 2021, 2022), three approaches were taken to operationalize outcome to account for limitations of each operationalization. Eating disorder diagnosis was chosen to characterize illness status.…”