Anorexia Nervosa

Anorexia nervosa is a severe eating disorder characterized by low body weight. Anorexia nervosa is diagnosed when a person's body weight falls below 85% of the ideal weight for that individual. The weight loss must be due to behavior directed at maintaining low weight or achieving a particular body image.

Epidemiology

The point prevalence of anorexia nervosa is between 0.5% and 1% in women, and more than 90% of patients with anorexia nervosa are women. The prevalence in men is not clear. Average age of onset is 17; onset is rare before puberty or after age 40.
Anorexia nervosa is more common in industrial societies and higher socioeconomic classes.

Etiology

Eating disorders and their subtypes likely share many common bases of origin. Psychological theories of anorexia nervosa remain speculative. Patients with anorexia nervosa generally have a high fear of losing control, difficulty with self-esteem, and commonly display"al1 or none" thinking. Although it is not specific to eating disorders, past physical or sexual abuse may be a risk factor. Contemporary theories focus on the need to control one's body.
Social theories propose that societal opinions, which equate low body weight with attractiveness, drive women to develop eating disorders. Although this fact may be responsible for some cases (e.g., anorexia nervosa is more common among dancers and models), historical1y anorexia nervosa has been present during periods when societal mores for beauty were different.

Biologic, familial, and genetic data support a biologic and heritable basis for anorexia. Family studies reveal an increased incidence of mood disorders and anorexia nervosa in first-degree relatives of patients with anorexia nervosa. Twin studies show higher concordance for monozygotic versus dizygotic twins.

Neuroendocrine evidence supporting a biologic contribution to anorexia includes alterations in corticotropin-releasing factor, reduced central nervous system norepinephrine metabolism, and that amenorrhea (caused by decreased luteinizing hormone and follicle-stimulating hormone release) sometimes precedes the onset of anorexia nervosa.

Clinical Manifestations

History and Mental Status Examination
DSM-IV criteria for the diagnosis of anorexia nervosa include refusal to keep body weight at greater than 85 % of ideal, an intense fear of weight gain, preoccupation with body size and shape, a disproportionate influence of body weight on personal worth, and the denial of the medical risks of low weight. Patients with anorexia nervosa generally do not have a loss of appetite; they refuse to eat out of fear of gaining weight. Amenorrhea is also a diagnostic criteria in postmenarchal females (delay of menarche may occur in premenarchal girls). In some cases, amenorrhea precedes the development of anorexia nervosa; however, in most cases, it appears to be a consequence of starvation.