Purging Disorder

Of interest, accuracy of the recall for self-induced vomiting frequency based on the EDE has been demonstrated to be very high,¹⁹ suggesting that the accuracy of lifetime diagnoses of purging disorder that do not require the presence of subjective binge-eating episodes also may be quite high. Several studies report high interrater reliability for interview assessments of bulimia nervosa and purging disorder using the EDE either for current diagnosis or for lifetime diagnosis.^1,2,7 Similar data have not been presented for the SCID-I.

Evidence that individuals with purging disorder display distinct physiological responses to a test meal compared with the responses of individuals who have bulimia nervosa further support the validity of a purging disorder diagnosis based on EDE assessment.² However, when assessments of food consumption are based entirely on self-report, it is likely that some individuals may exaggerate their food intake while others may be unwilling or unable to accurately describe the large amount of food they consume during binge-eating episodes. Finally, the determination of what constitutes a large amount of food can be quite subjective because this often depends on the context in which food is eaten.

In our laboratory, we have adopted a threshold of 1000 kcal within 2 hours, which reflects the upper limit of what healthy controls have been observed to eat within a 2-hour period in feeding laboratory studies24 as well as the upper limit of what college women endorse eating within a 2-hour period on a self-report questionnaire.²⁵ Using this limit reduces problems with interrater reliability, although it does not eliminate the problem of inaccurate self-report. Of note, this is not a unique problem in the diagnosis of purging disorder; it also can be quite challenging to evaluate whether reported episodes are large enough to qualify for a diagnosis of bulimia nervosa.

Treatment considerations
There have been no controlled treatment trials for purging disorder. Thus, there are no evidence-based treatments for this condition. Some have advocated a transdiagnostic cognitive-behavioral approach for the treatment of all eating disorders, and such an approach could be extended to the treatment of purging disorder.²⁶ A central tenet of cognitive-behavioral therapy is the use of repeated assessments throughout treatment to examine whether interventions are favorably impacting symptom levels. Whether a clinician chooses an approach that involves cognitive-behavioral, interpersonal, or psychodynamic interventions, it would be useful for clinicians to assess symptom levels throughout treatment in order to document the potential efficacy of a treatment that uses a single-case series approach (see Barlow and Hersen²⁷ for a detailed description of this approach). In such instances, clinicians can make important contributions to the field by describing possibly effective treatments that could be evaluated in larger randomized controlled trials.

Conclusion
Purging disorder is a form of eating disorder not otherwise specified in DSM-IV. At this time, it is unclear whether this will remain true following the publication of DSM-V. Key criteria for new diagnostic entities in DSM-V include evidence that doing so will improve a clinician's ability to care for patients in terms of understanding that a syndrome has a unique course, set of complications, or treatment needs.²⁸ At this time, we have limited data that suggest that the course of purging disorder is similar to that observed in bulimia nervosa over a 6-month prospective follow-up period and based on retrospective recall of lifetime data.^1,6 No data regarding complications of purging disorder have been reported thus far, although it seems reasonable that complications associated with purging behavior, such as hypokalemia, would be evident in this group.²⁹ Finally, as noted above, there are no data on evidence-based treatments for purging disorder. The absence of information on these topics is consistent with the adage that "we study what we define."³⁰

It is notable that information regarding the distinctive course, complications, and treatment response of anorexia nervosa versus bulimia nervosa emerged following the inclusion of these diagnoses in DSM rather than forming the justification for their initial inclusion. However, there are costs associated with the proliferation of diagnoses in subsequent editions of DSM in the absence of supportive data.

One possible solution would be the inclusion of purging disorder in the DSM-V appendix for criteria sets provided for further study. This approach yielded considerable data on binge-eating disorder following the publication of DSM-IV, such that arguments can be made regarding this syndrome's distinctive course and treatment response.³¹ Although this introduces the risk of reifying diagnostic criteria that have not themselves been adequately vetted,²⁸ this cost seems small in relation to the potential benefits of identifying evidence-based treatments for purging disorder. Published studies indicate that purging disorder affects a substantial minority of late adolescent girls and young women, with lifetime prevalence estimates that are on par with those for anorexia nervosa and bulimia nervosa.^6,32 Thus, it is crucial to develop a better understanding of how to help these individuals.