Study Sheds Light on Crossover Patterns

Anorexia nervosa (AN) and bulimia nervosa (BN) have overlapping clinical features as well as characteristics specific to each individual disorder. For example, the course of AN often includes the appearance of bulimic symptoms and a crossover to the full syndrome of BN. Even so, clinicians are still not able to predict which patients will develop BN. Even less is known about crossover from BN to AN.

Several differences in personality traits associated with the two disorders might influence crossover. For example, individuals with restricting-type AN tend toward rigidity and over-control, whereas those with BN tend toward impulsivity and affective deregulation. Persons with the binge-purge subtype of AN tend to fall between the two previous groups, particularly with regard to the degree of impulsivity.

A study to chart crossover

Pamela Keel, PhD, and 19 other clinicians recently designed a study to examine patients’ crossover from AN to BN and from BN to AN. The subjects were participants in the International Price Foundation Genetic Study of Bulimia Nervosa (Am J Psychiatry 2005;162:732). The researchers used two types of analyses. First, they explored patterns of crossover from AN to BN by comparing 56 individuals with persistent restricting-type AN and 32 individuals with an initial diagnosis of restricting-type AN who developed BN. Next, to study crossover from BN to AN, they compared 257 individuals meeting the criteria for a diagnosis of persistent normal-weight BN purging type and 93 patients who initially had normal-weight BN followed by the development of AN, purging type.

General patterns of crossover

For most individuals, crossover occurred by the fifth year of illness, and the crossover rate was higher from AN to BN than from BN to AN. The authors found that the proportion of persons with BN who eventually developed AN (27%) was substantially higher than rates reported in previous studies (Psychol Med 1992; 22:951; Psychosom Med 1987; 49:45). This suggested an elevated risk for diagnostic crossover in individuals with both AN and BN, but stabilization of the illness by the fifth year.

One factor, low self-directedness, was consistently associated with both types of crossover, according to the authors. This suggested that self-directedness might be a general characteristic that influences the course of the eating disorder. Individuals who have low self-directedness, independent of the diagnosis, may have an inability to regulate their behaviors and affect.

Crossover from AN to BN

Several factors were identified in the crossover from AN to BN, including low self-directedness and a high degree of parental criticism. Body mass index was not included in the analysis. Family factors, especially perceived criticism by parents, were particularly powerful. Families of patients with BN tend to have greater conflict and disorganization and less cohesion than AN families.

Crossover from BN to AN

Low scores on impulse-related personality traits (such as novelty-seeking) and the presence of such behaviors as alcohol abuse/dependence were important in the crossover from BN to AN. The authors hypothesize that lower-than-usual levels of impulsivity may enable the patient to maintain rigid dietary regimes long enough to lose the amount of weight necessary for a diagnosis of AN.

Some implications

If the findings from this exploratory study are confirmed, they may have important implications for treatment. For example, low self-directedness has been associated with a negative outcome. High self-directedness predicts rapid and sustained response to cognitive behavioral therapy (CBT) in BN patients and there is evidence that CBT leads to increased self-directedness (Compr Psychiatry 2002;43:182). Thus, self-directedness may influence not only the diagnostic stability of these eating disorders but also their course and response to treatment. Techniques designed to improve intrafamilial communication in cases of AN and addressing impulsivity in BN may also promote diagnostic stability and possibly shorten recovery times.