Among women, the lifetime prevalence of the full syndrome of AN is approximately 1%. AN is much less common in males. AN is more prevalent in cultures where food is plentiful and being thin is associated with attractiveness. Individuals who pursue interests that place a premium on thinness, such as ballet and modeling, are at greater risk. The incidence of AN has increased in recent decades.
The etiology of AN is unknown but appears to involve a combination of psychological, biologic, and cultural risk factors. Some factors, such as sexual or physical abuse and a family history of mood disturbance, are best viewed as nonspecific risk factors that increase vulnerability to a range of psychiatric disorders, including AN.
Patients who develop AN are inclined to be more obsessional and perfectionist than their peers. The disorder often begins as a diet not distinguishable at the outset from those undertaken by many adolescents and young women. As weight loss progresses, the fear of gaining weight grows; dieting becomes stricter; and psychological, behavioral, and medical aberrations increase. Eating disorders, including AN, may develop among individuals with type 1 diabetes mellitus and are associated with poorer glycemic control and an increased frequency of complications (Chap. 344).
Numerous physiologic disturbances, including abnormalities in a variety of neurotransmitter systems, have been described in AN (see below). It is difficult to distinguish neurochemical, metabolic, and hormonal changes that may have a role in the initiation or perpetuation of the syndrome from those that are secondary to the disorder. The resolution of most of these abnormalities with weight restoration argues against an etiologic role.
Genetic factors contribute to the risk of development of AN, as its incidence is greater in families with one affected member and the concordance in monozygotic twins is greater than in dizygotic twins. However, specific genes or risk factor loci have not been identified.
AN typically begins in mid to late adolescence, sometimes in association with a stressful life event such as leaving home for school (Table 79-1). The disorder occasionally develops in early puberty, before menarche, but seldom begins after age 40. Despite being underweight, patients with AN are irrationally afraid of gaining weight. They also exhibit a distortion of body image; despite being emaciated, patients with AN may believe that their body as a whole, or some part of their body, is too fat. Further weight loss is viewed by the patient as a fulfilling accomplishment, whereas weight gain is seen as a personal failure. Patients with AN rarely complain of hunger or fatigue and often exercise extensively. Despite the denial of hunger, one-quarter to one-half of patients with AN engage in eating binges. Patients tend to become socially withdrawn and increasingly committed to work or study, dieting, and exercise. As weight loss progresses, thoughts of food dominate mental life and idiosyncratic rules develop around eating. Patients with AN may obsessively collect cookbooks and recipes and be drawn to food-related occupations.
Table 79-1 Common Characteristics of Anorexia Nervosa, Bulimia Nervosa, and Binge Eating Disorder |Favorite Table|Download (.pdf)
Table 79-1 Common Characteristics of Anorexia Nervosa, Bulimia Nervosa, and Binge Eating Disorder
|Anorexia Nervosaa||Bulimia Nervosa||Binge Eating Disorderb|
|Onset||Mid-adolescence||Late adolescence/early adulthood||Late adolescence/early adulthood|
|Lifetime prevalence||1% of women||1–3% of women||4% of men and women|
|Weight||Markedly decreased||Usually normal||Usually obese|
|Menstruation||Absent||Usually normal||Usually normal|
|Binge eating||25–50%||Required for diagnosis||Required for diagnosis|
|Mortality||∼5% per decade||Low||Low|
|Physical and laboratory findingsa|
|Skin/extremities||Lanugo||Callus/abrasion on dorsum of hand|
|Gastrointestinal||Salivary gland enlargement||Salivary gland enlargement|
|Slow gastric emptying||Dental erosion|
|Elevated liver enzymes|
|Hematopoietic||Normochromic, normocytic anemia|
|Fluid/Electrolyte||Increased BUN, creatinine||Hypokalemia|
|Low estrogen or testosterone|
|Low LH and FSH|
Patients with AN typically have few physical complaints but may note cold intolerance. Gastrointestinal motility is diminished, leading to reduced gastric emptying and constipation. Some women who develop AN after menarche report that their menses ceased before significant weight loss occurred. Weight and height should be measured to allow calculation of body mass index (BMI; kg/m2). Vital signs may reveal bradycardia, hypotension, and mild hypothermia. Soft, downy hair growth (lanugo) sometimes occurs, as does alopecia. Salivary gland enlargement, which is associated with starvation as well as with binge eating and vomiting, may make the face appear surprisingly full in contrast to the marked general wasting. Acrocyanosis of the digits is common, and peripheral edema can be seen in the absence of hypoalbuminemia, particularly when the patient begins to regain weight. Consumption of large amounts of vegetables containing vitamin A can result in a yellow tint to the skin (hypercarotenemia), which is especially notable on the palms.
Mild normochromic, normocytic anemia is frequent, as is mild to moderate leukopenia, with a disproportionate reduction of polymorphonuclear leukocytes. Dehydration may result in slightly increased levels of blood urea nitrogen and creatinine. Serum transaminase levels may increase, especially during the early phases of refeeding. The level of serum proteins is usually normal. Blood sugar is often low and serum cholesterol may be moderately elevated. Hypokalemia, often accompanied by alkalosis, suggests self-induced vomiting or use of diuretics. Hyponatremia is common and may result from excess fluid intake and disturbances in the secretion of antidiuretic hormone. Hypophosphatemia and hypomagnesemia may be present in severe AN, especially as part of a refeeding syndrome.
The regulation of virtually every endocrine system is altered in AN, but the most striking changes occur in the reproductive system. Amenorrhea is hypothalamic in origin and reflects diminished production of gonadotropin-releasing hormone (GnRH). The resulting gonadotropin deficiency causes low plasma estrogen in women and reduced testosterone in men. The hypothalamic GnRH pulse generator is exquisitely sensitive, particularly in women, to body weight, stress, and exercise, each of which may contribute to hypothalamic amenorrhea in AN (Chap. 347).
Serum leptin levels are markedly reduced in AN as a result of undernutrition and decreased body-fat mass. The reduction in leptin is the primary factor responsible for the disturbances of the hypothalamic-pituitary-gonadal axis, and an important mediator of the other neuroendocrine abnormalities characteristic of AN (Chap. 77).
Serum cortisol and 24-h urine-free cortisol levels are generally elevated but without characteristic clinical signs of cortisol excess. Thyroid function tests resemble the pattern seen in euthyroid sick syndrome (Chap. 341). Thyroxine (T4) and free T4 levels are usually in the low-normal range, triiodothyronine (T3) levels are reduced, and reverse T3 (rT3) is elevated. The level of thyroid-stimulating hormone (TSH) is normal or partially suppressed. Growth hormone is increased, but insulin-like growth factor 1 (IGF-1), which is produced mainly by the liver, is reduced, as in other conditions of starvation. Diminished bone density is routinely observed in AN and reflects the effects of multiple nutritional deficiencies, reduced gonadal steroids, increased cortisol, and reduced IGF-1. The degree of bone-density reduction is proportional to the length of the illness, and patients are at risk for the development of symptomatic fractures. The occurrence of AN during adolescence may lead to the premature cessation of linear bone growth and a failure to achieve expected adult height.
Cardiac output is reduced, and congestive heart failure occurs rarely during rapid refeeding. The electrocardiogram usually shows sinus bradycardia, reduced QRS voltage, and nonspecific ST-T-wave abnormalities. Some patients develop a prolonged QTc interval, which may predispose to serious arrhythmias, particularly when electrolyte abnormalities are present.
The diagnosis of AN is based on the presence of characteristic behavioral, psychological, and physical attributes (Table 79-2). Widely accepted diagnostic criteria are provided by the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). These criteria include maintenance of a less than minimally normal body weight for age and height. Weights less than 85% of that expected, roughly equivalent to a BMI of 18.5 kg/m2, are commonly considered to meet this criterion, but a patient weighing somewhat more who meets all other diagnostic criteria would still merit the diagnosis of AN. The current diagnostic criteria require that women with AN not have spontaneous menses, patients who have other characteristics of AN but report menstrual activity probably merit the diagnosis.
Table 79-2 Diagnostic Features of Anorexia Nervosa |Favorite Table|Download (.pdf)
Table 79-2 Diagnostic Features of Anorexia Nervosa
|Refusal to maintain body weight at or above a minimally normal weight for age and height. (This includes a failure to achieve weight gain expected during a period of growth leading to an abnormally low body weight.)|
|Intense fear of weight gain or becoming fat.|
|Distortion of body image (e.g., feeling fat despite an objectively low weight or minimizing the seriousness of low weight).|
|Amenorrhea. (This criterion is met if menstrual periods occur only following hormone—e.g., estrogen—administration.)|
The diagnosis of AN can usually be made confidently in a patient with a history of weight loss accomplished by restrictive dieting and excessive exercise accompanied by a marked reluctance to gain weight. Patients with AN often deny that they have a serious problem and may be brought to medical attention by concerned family or friends. Especially in atypical presentations, other causes of significant weight loss in previously healthy young people should be considered, including inflammatory bowel disease, gastric outlet obstruction, diabetes mellitus, CNS tumors, or neoplasm (Chap. 80).
The course and outcome of AN are highly variable. One-quarter to one-half of patients eventually recover fully, with few psychological or physical sequelae. However, many patients have persistent difficulties with weight maintenance, depression, and eating disturbances, including BN. The development of obesity following AN is rare. The long-term mortality of AN is among the highest associated with any psychiatric disorder. Approximately 5% of patients die per decade of follow-up, primarily due to the physical effects of chronic starvation or by suicide.
Virtually all of the physiologic abnormalities associated with AN are observed in other forms of starvation and markedly improve or disappear with weight gain. A worrisome exception is the reduction in bone mass, which may not recover fully, particularly if AN occurs during adolescence when peak bone mass is normally achieved.
Treatment: Anorexia Nervosa
Because of the profound physiologic and psychological effects of starvation, there is a broad consensus that weight restoration to at least 90% of predicted weight is the primary goal in the treatment of AN. Unfortunately, because most patients resist this goal, the management of AN is often accompanied by frustration for the patient, the family, and the physician. Patients typically exaggerate their food intake and minimize their symptoms. Some patients resort to subterfuge to make their weights appear higher, for example, by water-loading before they are weighed. In attempting to engage the patient in treatment, it may be useful to elicit the patient's physical concerns (e.g., about osteoporosis, weakness, or fertility), and provide education about the importance of normalizing nutritional status in order to address those concerns. The physician should reassure the patient that weight gain will not be permitted to get out of control but simultaneously emphasize that weight restoration is medically and psychologically imperative.
The intensity of the initial treatment, including the need for hospitalization, is determined by the patient's current weight, the rapidity of recent weight loss, and the severity of medical and psychological complications (Fig. 79-1). Hospitalization should be strongly considered for patients weighing <75% of that expected age and height, even if the results of routine blood studies are within normal limits. Acute medical problems, such as severe electrolyte imbalances, should be identified and addressed. Nutritional restoration can almost always be successfully accomplished by oral feeding, and parenteral methods are rarely required. For severely underweight patients, sufficient calories (approximately 1200–1800 kcal/d) should be provided initially in divided meals as food or liquid supplements to maintain weight and permit physiological stabilization. Calories can then be gradually increased to achieve a weight gain of 1–2 kg (2–4 lb) per week, typically requiring an intake of 3000–4000 kcal/d. Meals must be supervised, ideally by personnel who are firm regarding the necessity of food consumption, empathic regarding the challenges entailed, and reassuring about the patient's eventual recovery. Patients have great psychological difficulty complying with the need for increased caloric consumption, and the assistance of psychiatrists or psychologists experienced in the treatment of AN is usually necessary.
An algorithm for basic treatment decisions regarding patients with anorexia nervosa or bulimia nervosa. Based on the American Psychiatric Association practice guidelines for the treatment of patients with eating disorders. *Although outpatient management may be considered for patients with anorexia nervosa weighing more than 75% of expected, there should be a low threshold for using more intensive interventions if the weight loss has been rapid or if current weight is <80% of expected.
Less severely affected patients may be treated in a partial hospitalization program where medical and psychiatric supervision is available and several meals can be monitored each day. Outpatient treatment may suffice for mildly ill patients. Weight must be monitored at frequent intervals, and explicit goals agreed on for weight gain, with the understanding that more intensive treatment will be required if the level of care initially employed is not successful. For younger patients, the active involvement of the family in treatment is crucial regardless of treatment setting. Outpatient interventions that help parents refeed their child have been be quite successful at achieving weight restoration.
Psychiatric treatment focuses primarily on two issues. First, patients require much emotional support during the period of weight gain. They often intellectually agree with the need to gain weight, but strenuously resist increases in caloric intake, and often surreptitiously discard food that is provided. Second, patients must learn to base their self-esteem not on the achievement of an inappropriately low weight, but on the development of satisfying personal relationships and the attainment of reasonable academic and occupational goals. While this is often possible, some patients with AN develop other serious emotional and behavioral symptoms such as depression, self-mutilation, obsessive-compulsive behavior, and suicidal ideation. These symptoms may require additional therapeutic interventions, in the form of psychotherapy, medication, or hospitalization.
Medical complications occasionally occur during refeeding. Especially in the early stages of treatment, severely malnourished patients may develop a "refeeding syndrome" characterized by hypophosphatemia, hypomagnesemia, and cardiovascular instability. Acute gastric dilatation has been described when refeeding is rapid. As in other forms of malnutrition, fluid retention and peripheral edema may occur, but they generally do not require specific treatment in the absence of cardiac, renal, or hepatic dysfunction. Transient modest elevations in serum liver enzyme levels occasionally occur. Multivitamins should be given, and an adequate intake of vitamin D (400 IU/d) and calcium (1500 mg/d) should be provided.
No psychotropic medications are of established value in the treatment of AN, although there is recent preliminary evidence that the atypical antipsychotic medication olanzapine may assist some patients by increasing the rate of weight gain and decreasing obsessive thinking. Medications that may prolong the QTc interval should be avoided. The alterations of cortisol and thyroid hormone metabolism do not require specific treatment and correct with weight gain. Estrogen treatment appears to offer no benefit to bone density in underweight patients, and the small benefit of bisphosphonate treatment appears to be outweighed by the potential risks of such agents in young women.