Summary: While purging may be a characteristic of bulimia nervosa, a new study reports a different kind of eating disorder may also be responsible for purging behaviors.
Source: Ohio University
Though purging is often a condition associated with bulimia nervosa, new research at Ohio University suggests that a different kind of eating disorder could also be responsible.
The study, published in the International Journal of Eating Disorders, sought to differentiate the little understood “purging disorder” from the more well-documented bulimia nervosa, with which it is often confused.
The research was led by K. Jean Forney, an assistant professor of psychology in the College of Arts and Sciences at Ohio University who specializes in eating disorders.
Both purging disorder and bulimia nervosa are eating disorders characterized by self-induced vomiting and other types of purging. However, a central characteristic of bulimia is large, out-of-control eating episodes, whereas purging disorder isn’t defined by binge eating.
Moreover, purging is an essential attribute of purging disorder, whereas bulimia nervosa may include non-purging behaviors like fasting or excessive exercise.
“In both conditions, people are going to extreme lengths to control their weight,” Forney said.
Because bulimia nervosa is well understood, it is easily diagnosed in the Diagnostic and Statistical Manual of Mental Disorders (DSM), which is used to diagnose mental health disorders. Purging disorder, however, hasn’t been well researched, and thus falls into the more ambiguous “residual” categories of the DSM.
“People tend to think conditions in the residual category are less dangerous, but that isn’t true,” Forney said. “There is plenty of cross-sectional data that suggest that the purging disorder is just as serious as bulimia nervosa.”
Because of its relative obscurity in the psychiatric world, until it is better understood, people suffering from purging disorder do not have psychiatric or psychological treatments that have been tested for their specific symptom presentation. Forney hopes that that the current study can provide a starting point for future intervention-related research.
“Most of our eating disorder treatments focus on treating binge-eating. What we really need are treatments that do a better job treating symptoms when binge eating isn’t present and we don’t really have that right now,” she said.
Purging disorder was first researched and identified in 2005 by Pamela Keel, a psychology professor at Florida State University. Forney wanted to continue Keel’s initial research so that the prognosis of purging disorder could be better understood. To do so, Forney followed up with 217 women who participated in Keel’s original study.
The participants, who needed to meet the clinical criteria for purging disorder or bulimia nervosa, all participated in one of three studies conducted between 2000 and 2012.
Forney sought to predict the future behavior of those suffering from purging disorder by comparing long-term outcomes to those suffering from bulimia nervosa. The study found no significant difference in eating disorder presence, recovery status and level of eating pathology between diagnostic groups.
However, it concluded there are significant enough differences between bulimia nervosa and purging disorder to necessitate specific treatments for purging disorder. To do so, it is important to treat purging disorder as a full threshold eating disorder, the research stated.
It also found significant enough differences between bulimia nervosa and purging disorder that the interpretation of symptoms that lead to a diagnosis, known as clinical presentation, could be uniquely classified. Only a small proportion of women with purging disorder developed bulimia nervosa, indicating that these are distinct eating disorders.
“They’re equal in severity and chronicity but there are still differences in clinical presentation,” Forney said.
However, the study was not without limitations. “We didn’t find anything that predicted outcome,” Forney said, which she described as “disheartening.” “That means we need to do more work to determine what is keeping the eating disorder going – those are the factors we want to target in treatment.”
Despite setbacks, Forney is hopeful that her research will reignite further interest in purging disorder, and that future research will eventually lead to more effective treatment.
Evaluating the predictive validity of purging disorder by comparison to bulimia nervosa at long-term follow-up
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.
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.
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).
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.