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Anorexia nervosa is a psychiatric illness that describes an eating disorder characterized by extremely low body weight, body image distortion and an obsessive fear of gaining weight. Individuals with anorexia nervosa are known to control body weight commonly through the means of voluntary starvation.

The term anorexia is of Greek origin: a (α, prefix of negation), n (ν, link between two vowels) and orexis (ορεξις, appetite), thus meaning a lack of desire to eat.

Anorexia has a incidence of between 8 and 13 cases per 100,000 persons per year and an average prevalence of 0.3% using strict criteria for diagnosis. The condition largely affects young adolescent females, with females between 15 and 19 years old making up 40% of all cases. Furthermore, the majority of cases are unlikely to be in contact with mental health services. Approximately 90% of people with anorexia are female.

Definition

A definition of anorexia nervosa was established by the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and the World Health Organization's International Statistical Classification of Diseases and Related Health Problems (ICD).

DSM-IV-TR criteria are:
  • Refusal to maintain body weight at or above a minimally normal weight for age and height (e.g. weight loss leading to maintenance of body weight less than 85% of that expected; or failure to make expected weight gain during period of growth, leading to body weight less than 85% of that expected).
  • Intense fear of gaining weight or becoming fat, even though underweight.
  • Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or denial of the seriousness of the current low body weight.
  • Amenorrhea (at least three consecutive cycles) in postmenarchal girls and women. Amenorrhea is defined as periods occurring only following hormone (e.g., estrogen) administration.


Furthermore, the DSM-IV-TR specifies two subtypes:
  • Restricting Type: during the current episode of anorexia nervosa, the person has not regularly engaged in binge-eating or purging behavior (that is, self-induced vomiting, or the misuse of laxatives, diuretics, or enemas). Weight loss is accomplished primarily through dieting, fasting, or excessive exercise.
  • Binge-Eating Type or Purging Type: during the current episode of anorexia nervosa, the person has regularly engaged in binge-eating OR purging behavior (that is, self-induced vomiting, or the misuse of laxatives, diuretics, or enemas).


The ICD-10 criteria are similar, but in addition, specifically mention
  1. The ways that individuals might induce weight-loss or maintain low body weight (avoiding fattening foods, self-induced vomiting, self-induced purging, excessive exercise, excessive use of appetite suppressants or diuretics).
  2. Certain physiological features, including "widespread endocrine disorder involving hypothalamic-pituitary-gonadal axis is manifest in women as amenorrhoea and in men as loss of sexual interest and potency. There may also be elevated levels of growth hormones, raised cortisol levels, changes in the peripheral metabolism of thyroid hormone and abnormalities of insulin secretion".
  3. If onset is before puberty, that development is delayed or arrested.


The distinction between the diagnoses of anorexia nervosa, bulimia nervosa and eating disorder not otherwise specified (EDNOS) is often difficult to make in practice and there is considerable overlap between patients diagnosed with these conditions. Furthermore, seemingly minor changes in a patient's overall behavior or attitude can change a diagnosis from "anorexia: binge-eating type" to bulimia nervosa. It is not unusual for a person with an eating disorder to "move through" various diagnoses as his or her behavior and beliefs change over time.

Causes and contributory factors

Genetic factors

Family and twin studies have suggested that genetic and environmental factors account for 74% and 26% of the variance in anorexia nervosa, respectively. This evidence suggests that genes influencing both eating regulation, and personality and emotion, may be important contributing factors. In one study, variations in the norepinephrine transporter gene promoter were associated with restrictive anorexia nervosa, but not binge-purge anorexia (though the latter may have been due to small sample size).

Neurobiological factors

Anorexia may be linked to a disturbed serotonin system, particularly to high levels at areas in the brain with the 5HT1A receptor - a system particularly linked to anxiety, mood and impulse control. Starvation has been hypothesised to be a response to these effects, as it is known to lower tryptophan and steroid hormone metabolism, which might reduce serotonin levels at these critical sites and ward off anxiety. Other studies of the 5HT2A serotonin receptor (linked to regulation of feeding, mood, and anxiety), suggest that serotonin activity is decreased at these sites. There is evidence that both personality characteristics and disturbances to the serotonin system are still apparent after patients have recovered from anorexia.

Changes in brain structure and function are early signs often to be associated with starvation, and is partially reversed when normal weight is regained. Anorexia is also linked to reduced blood flow in the temporal lobes. It is possible that it is a risk trait rather than an effect of starvation.

Anorexia may be linked to an autoimmune response to melanocortin peptides which influence appetite and stress responses.

Nutritional factors

Zinc deficiency may play a role in Anorexia. It is not thought responsible for causation of the initial illness but there is evidence that it may be an accelerating factor that deepens the pathology of the anorexia. A 1994 randomized, double-blind, placebo-controlled trial showed that zinc (14 mg per day) doubled the rate of body mass increase compared to patients receiving the placebo.

Psychological factors

Anorexic eating behavior is thought to originate from an obsessive fear of gaining weight due to a distorted self imageRosen JC, Reiter J, Orosan P. (1995) Assessment of body image in eating disorders with the body dysmorphic disorder examination. Behav Res Ther, 1, 77-84. PMID 7872941.
and is maintained by various cognitive biases that alter how the affected individual evaluates and thinks about their body, food and eating. This is not a perceptual problem, but one of how the perceptual information is evaluated by the affected person. People with anorexia nervosa seem to more accurately judge their own body image while lacking a self-esteem boosting bias.

People with anorexia nervosa also have other psychological difficulties and mental illness. Clinical depression, obsessive compulsive disorder, substance abuse and one or more personality disorders may be the most likely conditions to be comorbid with anorexia. High-levels of anxiety and depression are likely to be present regardless of whether they fulfill diagnostic criteria for a specific syndrome.

Research into the neuropsychology of anorexia has indicated that many of the findings are inconsistent across studies and that it is hard to differentiate the effects of starvation on the brain from any long-standing characteristics. One finding is that those with anorexia have poor cognitive flexibility.

Other studies have suggested that there are some attention and memory biases that may maintain anorexia.

Social and environmental factors

Sociocultural studies have highlighted the role of cultural factors, such as the promotion of thinness as the ideal female form in Western industrialised nations, particularly through the media. A recent epidemiological study of 989,871 Swedish residents indicated that gender, ethnicity and socio-economic status were large influences on the chance of developing anorexia, with those with non-European parents among the least likely to be diagnosed with the condition, and those in wealthy, white families being most at risk. People in professions where there is a particular social pressure to be thin (such as models and dancers) were much more likely to develop anorexia during the course of their career, and further research has suggested that those with anorexia have much higher contact with cultural sources that promote weight-loss.

There is a high rate of reported child sexual abuse experiences in clinical groups of who have been diagnosed with anorexia. Although prior sexual abuse is not thought to be a specific risk factor for anorexia, those who have experienced such abuse are more likely to have more serious and chronic symptoms.

Relationship to autism

A summary of the strategy Zucker et al. (2007) used to assess the relationship between anorexia nervosa and the autism spectrum.
Since Gillberg's (1985) and others initial suggestion of relationship between anorexia nervosa and autism, a large scale longitudinal study into teenage onset anorexia nervosa conducted in Sweden confirmed that 23% of people with a long-standing eating disorder are on the autism spectrum. Those on autism spectrum tend to have a worse outcome, but may benefit from the combined use of behavioural and pharmacological therapies tailored to ameliorate autism rather than anorexia nervosa per se. Other studies, most notably research conducted at the Maudsley Hospitalmarker UKmarker, furthermore suggest that autistic traits are common in people with anorexia nervosa, shared traits include e.g. executive function, autism quotient score, central coherence, theory of mind, cognitive-behavioural flexibility, emotion regulation and understanding facial expressions.

Zucker et al. (2007) proposed that conditions on the autism spectrum make up the cognitive endophenotype underlying anorexia nervosa and appealed for increased interdisciplinary collaboration (see figure to right). A pilot study into the effectiveness Cognitive Behaviour Therapy, which based its treatment protocol on the hypothesised relationship between anorexia nervosa and an underlying autistic like condition, reduced perfectionism and rigidity in 17 out of 19 participants.

Prognosis

Anorexia is thought to have the highest mortality rate of any psychiatric disorder, with anywhere from 6-20% of those who are diagnosed with the disorder eventually dying due to related causes. The suicide rate of people with anorexia is also higher than that of the general population. In a longitudinal study women diagnosed with either DSM-IV anorexia nervosa (n = 136) or bulimia nervosa (n = 110) respectively who were assessed every 6 - 12 months over an 8 year period are at a considerable risk of committing suicide. Clinicians were warned of the risks as 15% of subjects reported at least one suicide attempt. It was noted that significantly more aneroxia (22.1%) than bulimia (10.9%) subjects made a suicide attempt.

Treatment

Treatment for anorexia nervosa tries to address three main areas. 1) Restoring the person to a healthy weight; 2) Treating the psychological disorders related to the illness; 3) Reducing or eliminating behaviours or thoughts that originally led to the disordered eating.

Drug treatments, such as SSRI or other antidepressant medication, have not been found to be generally effective for either treating anorexia, or preventing relapse although it has also been noted that there is a lack of adequate research in this area.

Family based treatment has also been found to be an effective treatment for adolescents with short term anorexia. At 4 to 5 year follow up one study shows full recovery rate of 60 - 90% with 10-15% remaining seriously ill. This compares favourable to other treatments such as inpatient care where full recovery rates vary between 33-55%.

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