Anorexia nervosa is characterized by underweight BMI, intense fear of gaining weight, and distorted perception of body image. Anorexia nervosa typically begins in the years between adolescence and young adulthood. Ninety percent of patients are female, most of middle and upper socioeconomic status.
The prevalence of anorexia nervosa is greater than previously suggested, since prior diagnostic criteria were more restrictive and individuals with anorexia often prefer to conceal their illness. Many adolescents have mild versions of the disorder without the severe weight loss. The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5) classifies the severity of anorexia according to BMI: mild, BMI 17–18.49; moderate, BMI 16–16.99; severe, BMI 15–15.99; extreme, BMI less than 15.
DSM-5 defines two subtypes of anorexia nervosa: binge-eating/purging type and restricting type. The binge-eating/purging subtype is characterized by recurrent episodes of binge-eating or purging (ie, self-induced vomiting and/or abuse of diuretics, laxatives, enemas, cathartics). The restricting subtype is characterized by dieting, fasting or excessive exercising without associated binge-eating or purging.
The cause of anorexia nervosa is not known. Although multiple endocrinologic abnormalities exist in patients with anorexia nervosa, most authorities believe they are secondary to malnutrition and not primary disorders. Most experts favor a primary psychiatric origin, but no hypothesis explains all cases. Comorbidity with depression, anxiety, or obsessive-compulsive disorder is not uncommon and can be particularly pernicious. The patient characteristically comes from a family whose members are highly goal-oriented. One theory holds that the patient's refusal to eat is an attempt to regain control of one's body in defiance of parental control. The patient's unwillingness to inhabit an “adult body” may also represent a rejection of adult responsibilities and the implications of adult interpersonal relationships. Patients are often perfectionistic in behavior and exhibit obsessional personality characteristics. Obsessional preoccupation with food is also common.