Diagnosis and Management of Anorexia Nervosa
Diagnostic Criteria
Anorexia nervosa is diagnosed when a patient meets all three DSM-5 criteria: persistent energy restriction causing significantly low body weight, intense fear of weight gain or behavior preventing weight gain, and disturbed body weight/shape perception or lack of recognition of the seriousness of low weight. 1
The Three Required DSM-5 Criteria
Criterion A (Weight): Persistent restriction of energy intake leading to body weight significantly below what is minimally expected for the patient's age, sex, developmental trajectory, and physical health 2, 1
Criterion B (Fear/Behavior): Either intense fear of gaining weight or becoming fat, or persistent behavior that interferes with weight gain despite already being at significantly low weight 2, 1
Criterion C (Perception): Disturbance in how body weight or shape is experienced, undue influence of body shape/weight on self-evaluation, or persistent lack of recognition of the seriousness of current low body weight 2, 1
Key Diagnostic Updates from DSM-IV
The DSM-5 removed the amenorrhea requirement, allowing diagnosis in males, prepubertal females, women on hormonal contraceptives, and postmenopausal women 1. The weight criterion now uses flexible language ("significantly low body weight") rather than rigid percentages, enabling clinicians to consider growth charts, BMI percentiles in youth, and clinical context 1.
Subtypes
- Restricting type: Weight loss achieved primarily through dietary restriction, fasting, and/or excessive exercise 1, 3
- Binge-eating/purging type: Regular binge eating and/or purging behaviors (self-induced vomiting, laxative/diuretic misuse), distinguished from bulimia nervosa by the presence of significantly low body weight 1, 3
Differential Diagnosis
Distinguish anorexia nervosa from avoidant/restrictive food intake disorder (ARFID), which involves weight loss without body image disturbance or fear of weight gain 1. Medical causes of weight loss (inflammatory bowel disease, hyperthyroidism, malignancy) lack the psychological features including fear of weight gain and body image disturbance 1. Patients with anorexia nervosa may present with delayed gastric emptying of solids, delayed small/large bowel transit, and occasionally mega-duodenum with absent migrating motor complexes 2, 1.
Medical Stabilization and Hospitalization Criteria
Admit patients for inpatient medical stabilization when BMI <15 kg/m², or when severe physiologic instability is present including bradycardia, hypotension, hypothermia, or electrolyte abnormalities. 3, 4
High-Risk Medical Complications
- Cardiac complications account for at least one-third of all deaths in anorexia nervosa 4
- Young people who have lost large amounts of weight or lost weight rapidly can develop hypothermia, bradycardia, hypotension, and other serious complications 3, 4
- Delayed gastric emptying and intestinal dysmotility are common and typically improve with nutritional rehabilitation 2, 1
Refeeding Considerations
Exercise significant caution to avoid escalating to invasive nutrition support in patients with functional symptoms, especially pain-predominant presentations, in the absence of objective biochemical disturbances. 2 Such escalation carries risks of iatrogenesis and does not improve global function, quality of life, or symptoms in clinical practice 2. Nutritional support should be provided alongside treatment of the main symptoms, with the understanding that gastrointestinal dysmotility (including mega-duodenum and absent MMCs) improves with increased nutritional intake 2, 1.
Psychotherapy
For adolescents with involved caregivers, use eating disorder-focused family-based treatment (FBT) as the primary psychotherapy approach. 4
For adults, use eating disorder-focused cognitive-behavioral therapy (CBT-E) as the primary psychotherapy approach. 4
Multidisciplinary Team Approach
An MDT approach including clinical psychology and liaison psychiatry expertise is ideal, particularly given the high prevalence of psychological distress, anxiety, depression, and poor coping mechanisms in this population 2.
Timing and Urgency
Early detection and immediate medical and psychological treatment are critical, as complications develop rapidly in malnourished adolescents 4. Mortality rates for eating disorders are among the highest for any psychiatric disorder 3.
Pharmacologic Options
Olanzapine is the most studied atypical antipsychotic for anorexia nervosa, with evidence showing decreased anxiety around eating, improved sleep, decreased rumination about food and body concerns, and weight gain at doses of 5 mg per day and above. 5
Atypical Antipsychotics
- Olanzapine, quetiapine, and risperidone appear safe with some evidence of positive effects on depression, anxiety, and core eating disorder psychopathology 6
- Olanzapine has shown marked improvements in both weight and psychological adjustment in severe cases 7
- At doses ≥5 mg daily, olanzapine decreased anxiety around eating, improved sleep, and decreased rumination, with morning sedation as the most common adverse effect 5
- Currently insufficient evidence confirms atypical antipsychotics consistently enhance weight gain, though individual case reports and open-label trials suggest benefit 6
SSRIs
Fluoxetine may help prevent relapse in weight-restored patients, but should only be used after weight restoration has been achieved. 4
Common Pitfall
Do not use SSRIs during the acute malnutrition phase; reserve them for relapse prevention after weight restoration 4. The primary challenge in pharmacologic research is persuading adequate numbers of anorexia nervosa patients to participate in trials 6.
High-Risk Demographics
Adolescent and young adult females ages 13-20 years are most affected, with a female-to-male ratio of approximately 9:1 3, 4. Adolescent girls in competitive sports and dancing face particularly high risk due to performance pressures combined with aesthetic expectations 4. Girls who diet are 18 times more likely to develop an eating disorder than non-dieters 4.