Examining the utility of narrowing anorexia nervosa subtypes for adults

Abstract

Objective

The purpose of this investigation was to examine whether narrowing the criteria of anorexia nervosa (AN) subtypes among adults based on further delineations of current binge eating and purging (i.e., binge eating only, purging only, binge eating and purging, and restricting only) improves the potential clinical utility of the current DSM-5 system that specifies two types (i.e., current binge eating and/or purging and restricting, specified as the absence of current binge eating and/or purging).

Method

Self-reported eating disorder and psychiatric symptoms based on the Eating Disorder Questionnaire were examined in 347 adults from a multisite clinical sample who met DSM-IV criteria for AN. Classification based on binge eating and purging symptoms yielded the following subtypes: 118 restricting only (AN-R; no current binge eating or purging); 133 binge eating and purging (AN-B & P; current binge eating and purging); 43 binge eating only (AN-B; current binge eating and no current purging); and 53 purging only (AN-P; current purging and no current binge eating).

Results

The AN-R group had lower current body mass index compared to AN-B & P and AN-P with no group differences in highest, lowest, or desired body mass index. The probability of amenorrhea was higher for the AN-R and AN-B & P groups than the AN-P group. The probability of diet pill use was elevated for the AN-B & P and AN-P groups compared to the AN-R group. The AN-P group also had a higher probability of fasting than the AN-R group. The probability of substance use including tobacco was lower in the AN-R group than the other three groups. No group differences were found on measures of hospitalization, body image, physical symptoms, exercise, or dieting behaviors.

Conclusions

These findings do not support the validity or clinical utility of classifying AN into narrower subtypes based on current binge eating, purging, and binge eating with purging given that few differences were found among groups who reported any combination of current binge eating and purging. Future research is needed to replicate these findings and to further examine the AN subtype classification schemes.

Introduction

Symptom heterogeneity within psychiatric diagnoses can complicate treatment if intervention approaches are effective for only certain patterns of symptoms. For this reason, delineating subgroupings within a diagnosis can facilitate a clearer understanding of co-occurring symptoms, longitudinal course, and prognosis as well as inform treatment approaches. Anorexia nervosa (AN), an eating disorder associated with significant medical and mortality risk [1], [2], [3], is often unresponsive to treatment and characterized by high rates of relapse [4]. Therefore, identifying meaningful subtypes is a potentially useful strategy to improve treatment efficacy.

Consistent with the previous version, the DSM-5 [5] designates two subtypes of AN: 1) a binge-eating and purging subtype (AN-BP), characterized by binge eating, purging (e.g., self-induced vomiting, misuse of laxatives or diuretics), or a combination of binge eating and purging symptoms in the past three months, and 2) a restricting subtype (AN-R), characterized by an absence of regular binge eating and/or purging in the three months prior to diagnosis. The process of revising the DSM-IV [6] criteria for DSM-5 resulted in a re-examination of the validity of the AN-R/AN-BP subtyping scheme as well as consideration of alternative subgrouping or staging strategies [7], [8], [9]. The AN-R and AN-BP subtypes were retained in DSM-5 given higher levels of suicidality [10], [11], impulsivity and substance use [11], [12], [13], [14], and co-occurring psychiatric symptoms [15], [16], [17] reported in AN-BP compared to AN-R samples. However, these findings have not consistently been replicated and contrary findings have been observed in several studies [18], [19], [20]. Similarly, although several prospective studies have observed that AN-BP is associated with poorer outcome than AN-R [4], [21], [22], [23], other studies have not observed this difference [24]. Empirical classification studies have also been inconsistent in their support of the validity of the AN-R/AN-BP subtypes. Taxometric studies have yielded inconsistent findings about whether AN-R and AN-BP (and bulimic behavior more generally) are distinct entities or exist on a continuum [25], [26], with some evidence from taxometric and latent structure analyses suggesting that AN-BP is more similar to bulimia nervosa than to AN-R [27], [28], [29]. In addition, considerable data suggest that subtypes remain inconsistent over time, with individuals with AN-R often crossing over into the AN-BP classification [7], [18], [30].

Although these inconsistent findings potentially challenge the validity of the DSM-5 subtyping schema, alternatively, they may be the result of heterogeneity within the AN subtypes. One potential strategy to increase the clinical utility of AN subtypes is to narrow the AN-BP subtype by further delineating this category into three subcategories: binge eating without purging (i.e., binge eating only), purging without binge eating (i.e., purging only), and both binge eating and purging (i.e., combined binge eating and purging). Although some previous cross-sectional studies of this type of delineation have suggested that AN samples of individuals who purge but do not binge eat resemble AN-BP samples in terms of eating disorder psychopathology, clinical features, and comorbidity [16], other investigations have found that purging may be associated with higher levels of psychopathology than binge eating [31]. Subclassifying AN into four categories (i.e., restricting, binge eating only, purging only, and binge eating combined with purging) may potentially reduce the heterogeneity within the current AN-BP subtype and strengthen the validity and clinical utility of these diagnostic subcategories. Alternatively, further delineation may not create meaningful subgroups and could reduce the clinical utility of the current subtypes specified in DSM-5.

The purpose of the current investigation was to examine the utility of narrowing subtypes of AN to “pure” groups based on binge eating, purging, binge eating combined with purging, and restricting (i.e., the absence of binge eating and/or purging) by comparing these groups on measures of associated eating disorder symptoms, weight history, treatment history, body image, physical symptoms, and substance use. Clinically relevant differences among these four categories may indicate the usefulness of further subclassification based on patterns of binge eating and purging symptoms within the AN-BP group.