An investigation of the joint longitudinal trajectories of low body weight, binge eating, and purging in women with anorexia nervosa and bulimia nervosa.

The longitudinal course of eating disorders is often chronic and characterized by substantial symptom fluctuation.1-4 Research commonly captures these fluctuations through the use of outcome categories (e.g., remission and relapse) and shifts in diagnostic labels.5,6 Crossover data suggest that 20-50% of individuals with an initial diagnosis of anorexia nervosa (AN) develop bulimia nervosa (BN) over time4, 7-9 and the rate of crossover between anorexia nervosa subtypes appears to be even higher.8, 10-12 Although individual symptom fluctuations drive these outcomes and diagnostic changes over time, few studies have examined the course of the individual eating disorder symptoms and none has reported on patterns of convergence and divergence in these symptoms over time. Empirical methods of classification, including latent class analysis and latent profile analysis, have been used to identify eating disorder types in cross-sectional research. The results from these studies suggest mixed support for the current diagnostic structure in the DSM-IV,13 and expanded our understanding of these classifications by examining potentially useful correlates of membership in the identified classes.14-19 Similar to these methods of empirically-deriving groups in cross-sectional research are methods that identify patterns of change in longitudinal research. These methods, known as longitudinal latent structure analyses, have only recently been applied to the study of eating disorders. Crosby and colleagues20 used such an approach to identify daily patterns of negative affect in a sample of women with bulimia nervosa. They identified nine unique patterns of daily negative affect and found that two of these patterns, stable high negative affect and increasing negative affect, were specifically associated with higher rates of binge eating and purging during that day. In another study, Cain, Epler, Steinley, and Sher21 identified patterns of change between different classes of eating-related psychopathology in a 4-year study of eating, weight, and shape concerns in female undergraduates. They found that the majority of individuals did not change class membership over time, and among those who did change, the shifts were typically to a less severe class. These studies demonstrate the ability of longitudinal latent structure analyses to provide unique information about symptom course. The purpose of the current investigation was to utilize a novel longitudinal latent structure analysis, which has not previously been applied to the study of eating disorders, to examine the longitudinal course of three hallmark eating disorder symptoms: low body weight, binge eating, and purging in women with eating disorders during 5 years of follow-up. We aimed to: (1) identify longitudinal course trajectories for each of these symptoms and (2) examine relationships among these symptom trajectories over time. We used data from the Massachusetts General Hospital (MGH) Longitudinal Study of Anorexia and Bulimia Nervosa, which prospectively followed a treatment-seeking sample of women with initial diagnoses of AN or BN. This unique dataset was selected due to the availability of prospective weekly longitudinal data for the three eating disorder symptoms of interest in a well-characterized clinical sample.