Anorexia Nervosa

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Diagnosis and reasoning

This adolescent girl has been brought in by her parents, due to concerns about her behavior; analysis of her symptoms suggest that this might very well be Anorexia Nervosa (AN). The Diagnostic and Statistical Manual of mental health, Fifth Edition (DSM-5) requires the presence of 3 very specific criteria to establish the diagnosis of AN. Firstly, restriction of energy intake leading to a significantly low body weight (in the context of the person's age, gender, development trajectory, and physical health) should be present. According to the dietary guidelines for Americans released in 2010, an active teenage girl requires an energy intake of 2400 calories per day; the daily intake of this patient is only 1500 calories despite having a body weight of 48.5kg; thus, the above criterion is fulfilled. Secondly, there should be an intense fear of gaining weight, along with persistent behaviour that interferes with weight gain, even though the patient is at a significantly low weight already. Her stated fear of becoming fat, and the excessive exercise regime both fit this criterion. Thirdly, there should be a disturbance in the way in which one's body weight or shape is experienced, along with undue influence of body weight or shape on self-evaluation, or persistent lack of recognition of the seriousness of the current low body weight. Note that this patient believes that she does not put in enough effort to remain slim. Thus, all 3 criteria are fulfilled, allowing us to establish the presence of AN. Note also the positive family history of bulimia nervosa and her perfectionistic personality; both of these are strong risk factors for AN. Examination reveals the presence of sinus bradycardia; this is most probably due to reduction of the basal metabolic rate, secondary to severe AN. A follow up ECG is essential, as cardiac arrhythmias directly contribute to the high mortality in AN; Fortunately there are no concerning changes such as prolongation of the QT interval. As the body weight of this patient is less than 75% of the ideal, it is prudent to perform liver function tests (LFT). This is because these patients are at risk of hepatic steatosis due to the disturbed hepatic biosynthesis of lipoproteins, essential fatty acid deficiencies and lowered antilipolytic effect of insulin. Fortunately, her liver profile only shows a minimally elevated alanine transaminase (ALT) level; this is frequently seen in AN, and in isolation is not a cause for concern. In addition, the ultrasound scan shows no evidence of a fatty liver. Osteoporosis is a serious complication encountered in over half of patients with AN, and is ideally performed in individuals who have been underweight for 6 months or more; and indeed, a screening DEXA scan in this patient reveals the presence of mild osteopenia. In patients in whom the binging-purging type of AN is suspected, estimation of serum amylase may be helpful; due to increased secretion by the salivary glands, this will be elevated. However, this patient's symptoms are more suggestive of the restrictive type of AN; thus, the above test is probably unnecessary. Considering her management, she meets two of the the American Academy of Paediatrics (AAP) criteria for in-hospital management: a body weight < 75% ideal bodyweight, and a heart rate <50 bpm. Note that re-feeding should be performed slowly, in order to prevent the potentially life threatening "refeeding syndrome". Fluoxetine has no role in the treatment of AN; in addition, most current guidelines do not recommend osteoporosis prophylaxis with bisphosphonates in these patients.


Discussion

Anorexia Nervosa (AN) is one of the most common eating disorders, affecting between 0.3% to 1% of all women; it is also the psychiatric condition with the highest mortality, with as many as 10% of affected individuals dying within 10 years of diagnosis. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), AN is characterized by the following features: - Restriction of energy intake relative to requirements, leading to a significantly low body weight (in the context of the person's age, gender, development trajectory, and physical health) - An intense fear of gaining weight or of becoming fat, or persistent behavior which interferes with weight gain, even though the patient is already at a significantly low weight. - Disturbances in the way in which the patient experiences his or her body weight or shape, undue influence of body weight or shape on self-evaluation, or persistent lack of recognition of the seriousness of the current low body weight. Note that the presence of amenorrhea is no longer a diagnostic criterion in the DSM-5. There are several theories as to how AN develops; the action-outcome theory postulates that the eating behaviors of these individuals begin as goal directed actions, which lead to weight loss; this is considered to be highly rewarding. As explained by the stimulus-response learning theory, these behaviours become habitual when carried out persistently and repeatedly; the habits formed thus, are resistant to change, and aid in persistence of the disorder. Note also that AN can also be divided into two main subtypes: the restrictive type, where there is marked reduction of food intake, and the binging/purging type, which is characterized by self induced vomiting, laxative or diuretic abuse, or strenuous exercise. In women, the age of onset is approximately 19 years; affected individuals present with a wide variety of symptoms, including fatigue, dizziness, palpitations, insomnia, bloating, constipation, and amenorrhea. The physical examination can be unremarkable, except for a low body mass index (BMI); patients with the binging-purging form of the disease may have scars on the dorsum of the hands, eroded dental enamel, and enlarged salivary glands; these are secondary to repeated, self induced vomiting. Note also that individuals with severe disease may be bradycardic, secondary to a decrease in the basal metabolic rate. AN can give rise to a myriad of complications; in particular, cardiac arrhythmias are seen in almost 80% of patients, and contribute to the high mortality encountered in the condition. Other key complications include a reduction in thyroid metabolic activity, osteopenia and osteoporosis, and loss of both white and grey matter, leading to impairment of cognitive function. Last but not least, it should be appreciated that patients with AN are at high risk of death due to suicide. Laboratory investigations do not aid the diagnosis, but are of use in detecting complications of the disease; these include a electrolyte profile to detect any electrolyte disturbances, a liver profile and ultrasound scan of the abdomen to detect a fatty liver, and serum amylase levels to detect hyperamylasemia. Note also that dual-energy x-ray absorptiometry (DEXA) should be performed in patients who have been underweight for more than six months, so as to detect bone loss; cerebral imaging may be required in patients who have persisting neuropsychiatric symptoms, despite weight restoration. Studies suggest that the initial management of these patients should focus on prompt (but not over-hasty) restoration of weight; ideally, 0.5 to 1kg should be gained each month. Close monitoring is warranted during refeeding to prevent, detect, and treat "refeeding syndrome", which can range from minor transient pedal edema to serious cardiopulmonary dysfunction. Note that inpatient management has not been shown to be significantly advantageous over outpatient treatment. That said, the American Academy of Pediatrics (AAP) recommends that individuals with the following criteria be hospitalized: refusal to eat; <75% ideal body weight or ongoing weight loss despite intensive management; body fat <10%; heart rate <50 bpm; systolic blood pressure <90mmHg; temperature <96 °F; orthostatic changes in pulse; or arrhythmias. Psychotherapy should be commenced once weight gain has begun; cognitive behavioural therapy (CBT), family therapy, and interpersonal therapy are the most useful modalities. Note that there is limited evidence regarding the use of medications to restore weight, prevent relapse, and treat chronic AN; however, several non-controlled studies suggest Olanzapine may improve weight gain, and alleviate symptoms of depression, and obsessional thoughts. Overall, up to 50% of patients with AN do not show evidence of an eating disorder 10 years after successful treatment. The remainder do not improve, or demonstrate symptoms of a subclinical eating disorder, or develop another eating disorder.


Take home messages

  1. Anorexia nervosa carries the highest mortality among psychiatric disorders.
  2. Most patients do not complain of an eating disorder; a high degree of clinical suspicion is essential for detection.
  3. Refeeding should be initiated slowly and gradually in order to prevent onset of the potentially deadly "refeeding syndrome".

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