(See also Introduction to Eating Disorders.)
Anorexia nervosa occurs predominantly in girls and young women. Onset is usually during adolescence and rarely after age 40.
Two types of anorexia nervosa are recognized:
Restricting type: Patients restrict food intake but do not regularly engage in binge eating or purging behavior; some patients exercise excessively.
Binge eating/purging type: Patients regularly binge eat and/or induce vomiting and/or misuse laxatives, diuretics, or enemas.
Binges are defined as consumption of a much larger amount of food than most people would eat in a similar time period under similar circumstances with loss of control, ie, perceived inability to resist or stop eating.
Etiology of Anorexia Nervosa
The etiology of anorexia nervosa is unknown.
Other than being female, few risk factors have been identified. In some cultures, obesity is considered unattractive and unhealthy, and the desire to be thin is pervasive, even among children. More than 50% of prepubertal girls in the US diet or take other measures to control their weight. Excessive concern about weight or a history of dieting appears to indicate increased risk, and there is a genetic predisposition, and genome-wide studies have begun to identify specific loci that are associated with increased risk.
Family and social factors probably play a role. Many patients belong to middle or upper socioeconomic classes, are meticulous and compulsive, have average intelligence, and have very high standards for achievement and success.
Pathophysiology of Anorexia Nervosa
Endocrine abnormalities are common in anorexia nervosa; they include
Low levels of gonadal hormones
Mildly reduced levels of thyroxine (T4) and triiodothyronine (T3)
Increased cortisol secretion
Menses usually cease, but cessation of menses is no longer a criterion for diagnosis. Bone density declines. In severely undernourished patients, virtually every major organ system may be affected. However, susceptibility to infections is typically not increased.
Dehydration and metabolic alkalosis may occur, and serum potassium and/or sodium may be low; all are aggravated by induced vomiting and laxative or diuretic use.
Cardiac muscle mass, chamber size, and output decrease; mitral valve prolapse is commonly detected. Some patients have prolonged QT intervals (even when corrected for heart rate), which, with the risks imposed by electrolyte disturbances, may predispose to tachyarrhythmias. Sudden death, most likely due to ventricular tachyarrhythmias, may occur.
Symptoms and Signs of Anorexia Nervosa
Anorexia nervosa may be mild and transient or severe and persistent.
Even though underweight, most patients are concerned that they weigh too much or that specific body areas (eg, thighs, buttocks) are too fat. They persist in efforts to lose weight despite reassurances and warnings from friends and family members that they are thin or even significantly underweight, and they view any weight gain as an unacceptable failure of self-control. Preoccupation with and anxiety about weight increase even as emaciation develops.
Anorexia is a misnomer because appetite often remains until patients become significantly cachectic. Patients are preoccupied with food:
They may study diets and calories.
They may hoard, conceal, and waste food.
They may collect recipes.
They may prepare elaborate meals for other people.
Patients often exaggerate their food intake and conceal behavior, such as induced vomiting. Binge eating/purging occurs in 30 to 50% of patients. The others simply restrict their food intake.
Many patients with anorexia nervosa also exercise excessively to control weight. Even patients who are cachectic tend to remain very active (including pursuing vigorous exercise programs).
Reports of bloating, abdominal distress, and constipation are common. Most women with anorexia nervosa stop having menstrual periods. Patients usually lose interest in sex. Depression occurs frequently.
Common physical findings include bradycardia, low blood pressure, hypothermia, lanugo hair (soft, fine hair usually found only on neonates) or slight hirsutism, and edema. Body fat is greatly reduced. Patients who vomit frequently may have eroded dental enamel, painless salivary gland enlargement, and/or an inflamed esophagus.
Diagnosis of Anorexia Nervosa
Clinical criteria
Not recognizing the seriousness of the low body weight and restrictive eating are prominent features of anorexia nervosa. Patients resist evaluation and treatment; they are usually brought to the physician’s attention by family members or by intercurrent illness.
Clinical criteria for diagnosis of anorexia nervosa (1) include the following:
Restriction of food intake resulting in a significantly low body weight
Fear of excessive weight gain or obesity (stated specifically by the patient or manifested as behavior that interferes with weight gain)
Body image disturbance (misperception of body weight and/or appearance) or denial of the seriousness of illness
In adults, low body weight is defined using the body mass index (BMI). BMI of < 17 kg/m2 is considered significantly low; BMI 17 to < 18.5 kg/m2 may be significantly low depending on the patient's starting point.
For children and adolescents, the BMI percentile for age is used; the 5th percentile is usually given as the cutoff. However, children above the 5th percentile who have not maintained their projected growth trajectory may also be considered to meet the criterion for low body weight; BMI percentile for age tables and standard growth charts are available from the Centers for Disease Control and Prevention (see CDC Growth Charts). Separate BMI calculators are available for children and adolescents.
Patients may otherwise appear well and have few, if any, abnormalities in blood tests. The key to diagnosis is identifying persistent active efforts to avoid weight gain and an intense fear of fatness that is not diminished by weight loss.
Differential diagnosis
Another psychiatric disorder, such as schizophrenia or primary depression, may cause weight loss and reluctance to eat, but patients with these disorders do not have a distorted body image.
Rarely, an unrecognized severe physical disorder may cause substantial weight loss. Disorders to consider include malabsorption syndromes (eg, due to inflammatory bowel disease or celiac disease), new-onset type 1 diabetes, adrenal insufficiency, and cancer. may cause similar symptoms.
Diagnosis reference
1. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition Text Revision, DSM-5-TRTM, Feeding and eating disorders.
Prognosis for Anorexia Nervosa
Mortality rates are high, approaching 10% per decade among affected people who come to clinical attention; unrecognized mild disease probably rarely leads to death. With treatment, prognosis is as follows:
Half of patients regain most or all of lost weight, and any endocrine and other complications are reversed.
About one fourth have intermediate outcomes and may relapse.
The remaining one fourth have a poor outcome, including relapses and persistent physical and mental complications
Children and adolescents treated for anorexia nervosa have better outcomes than adults.
Treatment of Anorexia Nervosa
Nutrition supplementation
Psychotherapy (eg, cognitive behavioral therapy)
For children and adolescents, family-based treatment
Sometimes 2nd-generation antipsychotics
Treatment of anorexia nervosa may require life-saving short-term intervention to restore body weight. When weight loss has been severe or rapid or when weight has fallen below about 75% of recommended weight, prompt restoration of weight becomes critical, and hospitalization should be considered. If any doubt exists, patients should be hospitalized.
Outpatient treatments may include varying degrees of support and supervision and commonly involve a team of practitioners.
Nutritional supplementation is often used with behavioral therapy that has clear weight-restoration goals. Nutritional supplementation begins by providing about 30 to 40 kcal/kg/day; it can produce weight gains of up to 1.5 kg/week during inpatient care and 0.5 kg/week during outpatient care. Oral feedings using solid foods are best; many weight restoration plans also use liquid supplements. Very resistant, undernourished patients occasionally require nasogastric tube feedings.
Once nutritional, fluid, and electrolyte status has been stabilized, long-term treatment begins. Outpatient psychotherapy is the cornerstone of treatment. Treatments should emphasize behavioral outcomes such as normalized eating and weight. Treatment should continue for a full year after weight is restored. Results are best in adolescents who have had the disorder < 6 months.
Family therapy, particularly using the Maudsley model (also called family-based treatment), is useful for adolescents. This model has 3 phases:
Family members are taught how to refeed the adolescent (eg, through a supervised family meal) and thus restore the adolescent’s weight (in contrast to earlier approaches, this model does not assign blame for the development of the disorder to the family or the adolescent).
Control over eating is gradually returned to the adolescent.
After the adolescent is able to maintain the restored weight, therapy focuses on engendering a healthy adolescent identity.
Treatment of anorexia nervosa is complicated by patients' abhorrence of weight gain and denial of illness. The physician should attempt to provide a calm, concerned, stable relationship while firmly encouraging a reasonable caloric intake.
Treatment also involves regular follow-up monitoring and often a team of health care practitioners, including a nutritionist, who may provide specific meal plans or information about the calories needed to restore weight to a normal level.
Key Points
Patients with anorexia nervosa have an intense fear of gaining weight or becoming fat that persists despite all evidence to the contrary.
In the restricting type of anorexia nervosa, patients restrict food intake and sometimes exercise excessively but do not regularly engage in binge eating or purging.
In the binge eating/purging type, patients regularly binge eat and/or induce vomiting and/or misuse laxatives, diuretics, or enemas in an attempt to purge themselves of food.
In adults, BMI is significantly low (usually BMI of < 17 kg/m2), and in adolescents, BMI percentile is low (usually < 5th percentile) or does not increase as expected for normal growth.
Endocrine or electrolyte abnormalities or cardiac arrhythmias may develop, and death can occur.
