Other possible causes of significant weight loss should be considered in the differential diagnosis of Anorexia Nervosa, especially when the presenting features are atypical (such as an onset of illness after age 40 years). In general medical conditions (e.g., gastrointestinal disease, brain tumors, occult malignancies, and acquired immunodeficiency syndrome [AIDS]), serious weight loss may occur, but individuals with such disorders usually do not have a distorted body image and a desire for further weight loss. The superior mesenteric artery syndrome (characterized by postprandial vomiting secondary to intermittent gastric outlet obstruction) should be distinguished from Anorexia Nervosa, although this syndrome may sometimes develop in individuals with Anorexia Nervosa because of their emaciation. In Major Depressive Disorder, severe weight loss may occur, but most individuals with Major Depressive Disorder do not have a desire for excessive weight loss or excessive fear of gaining weight. In Schizophrenia, individuals may exhibit odd eating behavior and occasionally experience significant weight loss, but they rarely show the fear of gaining weight and the body image disturbance required for a diagnosis of Anorexia Nervosa.
Some of the features of Anorexia Nervosa are part of the criteria sets for Social Phobia, Obsessive-Compulsive Disorder, and Body Dysmorphic Disorder. Specifically, individuals may be humiliated or embarrassed to be seen eating in public, as in Social Phobia; may exhibit obsessions and compulsions related to food, as in Obsessive-Compulsive Disorder; or may be preoccupied with an imagined defect in bodily appearance, as in Body Dysmorphic Disorder. If the individual with Anorexia Nervosa has social fears that are limited to eating behavior alone, the diagnosis of Social Phobia should not be made, but social fears unrelated to eating behavior (e.g., excessive fear of speaking in public) may warrant an additional diagnosis of Social Phobia. Similarly, an additional diagnosis of Obsessive-Compulsive Disorder should be considered only if the individual exhibits obsessions and compulsions unrelated to food (e.g., an excessive fear of contamination), and an additional diagnosis of Body Dysmorphic Disorder should be considered only if the distortion is unrelated to body shape and size (e.g., preoccupation that one’s nose is too big).
In Bulimia Nervosa, individuals exhibit recurrent episodes of binge eating, engage in inappropriate behavior to avoid weight gain (e.g., self-induced vomiting), and are overly concerned with body shape and weight. However, unlike individuals with Anorexia Nervosa, Binge-Eating/Purging Type, individuals with Bulimia Nervosa are able to maintain body weight at or above a minimally normal level.