Anorexia Nervosa
High-Yield Comparison Between Eating Disorders
| Feature | Anorexia nervosa | Bulimia nervosa | Binge-eating disorder |
|---|---|---|---|
| Body weight | Significantly low body weight | Usually normal | No diagnostic weight requirement |
| Restricted intake | Core feature | May occur between binges as compensation | Not a core requirement |
| Binge eating | May occur in binge-eating/purging subtype | Required | Required |
| Compensatory behaviours (e.g. self-induced vomiting, excessive exercise) | May occur | Required | Absent |
| Weight gain / body-image concerns | Core feature (fear of weight gain + body image / weight disturbance) | Core feature (body image / weight disturbance) (fear of weight gain is NOT a core feature) | Not required |
| One-liner exam discriminator | Significantly low body weight + energy restriction (e.g. fasting) + fear of weight gain / body-image disturbance +/- binge eating or purging | Relatively normal body weight + binge eating + compensatory behaviours (e.g. excessive exercise, purging) + body-image disturbance | Recurrent binge eating without compensatory behaviours |
Causes and Risk Factors
The exact underlying cause of eating disorders is NOT fully understood.
Risk factors include: [Ref]
- Females in early adolescence (10-15x risk)
- Low BMI in childhood and pre-adolescence (one of the strongest predictors)
- +ve Family history (28-74% cases are heritable)
- Shared genetic risk with other psychiatric conditions (OCD, depression, bipolar, schizophrenia, autism)
- Core psychological drivers
- Fear of becoming overweight
- Drive for perfection
- Low self-worth (believing one does not “deserve” to eat)
- Experiencing the following in childhood
- Anxiety
- Obsessive-compulsive features
- Social difficulties
- Those who take part in activities associated with a high risk of eating disorders (e.g. professional sport, fashion, dance, or modelling)
The onset of the full syndrome is often precipitated by a combination of: [Ref]
- Physical triggers like menarche and exposure to food restriction
- Social / psychological triggers like stress, social pressure
Clinical Features and Diagnosis
DSM-5 Criteria
DSM-5 criteria for anorexia nervosa (ALL must be met): [Ref]
- Restriction of energy intake → significantly low body weight (in the context of age, sex, developmental trajectory and physical health)
- Importantly, DSM-5 does not require a specific BMI cut-off for diagnosis
- Intense fear of gaining weight / becoming fat OR persistent behaviour that interferes with weight gain
- At least 1 disturbance relating to weight / body shape
- Disturbed by one’s body weight or shape
- Self-worth influenced by body weight or shape
- Persistent lack of recognition of seriousness of low body weight
There are 2 specific subtypes of anorexia nervosa: [Ref]
| Restricting type |
|
| Binge-eating / purging type |
|
There is no minimum duration requirement for anorexia nervosa itself. The 3-month period above is for determining the subtype, not for making the diagnosis.
Anorexia nervosa requires restriction of energy intake (e.g. dieting, fasting) resulting in significantly low body weight.
Patients may additionally have recurrent binge-eating and/or purging behaviours (binge-eating/purging subtype). Therefore, the presence of binge eating or purging does not automatically indicate bulimia nervosa.
DSM-5 severity of anorexia nervosa in adults is specified using current BMI. Note that there is no fixed BMI cut-off required for the diagnosis itself:
- Mild: BMI ≥17 kg/m²
- Moderate: BMI 16–16.99 kg/m²
- Severe: BMI 15–15.99 kg/m²
- Extreme: BMI <15 kg/m²
Other Clinical Features
The following features can be seen in anorexia nervosa, but are not part of the DSM-5 criteria: [Ref]
| Category | Features |
|---|---|
| Physical signs |
|
| Dermatological features |
|
| Non-diagnostic eating and dietary behaviours |
|
| Emotional and cognitive symptoms |
|
Clinical features from purging behaviour (in purging type anorexia nervosa):[Ref]
- Dental erosions, dental caries (due to chronic exposure to gastric acid)
- Sialadenosis (bilateral painless parotid enlargement)
- Russell’s sign (calluses over the knuckles) – from repeated friction and mechanical scraping of the knuckles against the upper incisor teeth when using fingers to stimulate the gag reflex
- Acid-base disturbances
- Laxative abuse → hypokalaemic metabolic acidosis
- Self-induced vomiting / diuretic abuse → hypokalaemic metabolic alkalosis
Complications
Acute Complications
Key acute complications: [Ref1][Ref2]
- Electrolyte disturbances (from chronic starvation and purging behaviours)
- Hypokalaemia
- Hypophosphataemia
- Hyponatraemia
- Cardiovascular instability
- Electrolyte disturbances (esp. hypokalaemia) can cause QTc prolongation and arrhythmias (e.g. TdP)
- Sinus bradycardia and hypotension (from the body down-regulating metabolism to preserve energy)
- Metabolic disturbances
- Hypothermia
- Hypoglycaemia
- AKI (from severe dehydration, due to restrictive or purging behaviours)
Refeeding syndrome is an important complication if nutrition / feeding is reintroduced too rapidly after prolonged starvation.
Chronic Complications
Key chronic complications: [Ref1][Ref2]
- Hypothalamic hypogonadism, which can lead to
- Osteoporosis and osteopaenia
- Infertility
- Impaired growth, delayed puberty
- Pancytopaenia / bone marrow suppression from malnutrition
- Persistent bradycardia and hypotension
- ↑ Lifetime mortality
- Anorexia nervosa has one of the highest mortality rates among all eating and psychiatric disorders
- 20-30% of deaths result from suicide, and the rest from chronic starvation-associated complications
Initial Assessment and Referral
Anorexia nervosa can be a medical emergency due to severe dietary restriction, malnutrition and/or compensatory behaviours.
Key severe complications include severe dehydration (→ hypovolaemia), electrolyte disturbances (esp. hypokalaemia), arrhythmias, and risk of refeeding syndrome (see complications section above for more details).
First, assess whether the patient requires immediate emergency admission for inpatient care
- Key assessment / investigations
- Physical examination + observations
- BMI or weight (including rate of weight loss)
- U&Es for electrolyte levels
- ECG
- Key indications for immediate emergency admission for inpatient care:
- Clinically unstable
- Severe malnutrition
- Rapid weight loss (>1 kg per week)
- Severe dehydration
- Severe electrolyte disturbances (e.g. severe hypokalaemia, hyponatraemia, hypophosphataemia)
- ECG showing
- Significant QTc prolongation
- Arrhythmias
- Severe bradycardia (<40 bpm)
If immediate emergency is NOT necessary → refer immediately to a community-based, age-appropriate eating disorder service
If an eating disorder places the patient’s physical health at serious risk, but they refuse necessary inpatient treatment, consider compulsory treatment under the appropriate legal framework
- Adults: see the Mental Health Act (MHA) 1983
- Children and young people: see the Mental Health Act (MHA) 1983 or the Children Act 1983
Management
Key management goal: reaching a healthy body weight or BMI for their age
Do NOT offer pharmacological management to treat anorexia nervosa itself
Pharmacological management might be appropriate to manage comorbidities (e.g. depression)
Children and Young People (<18 y/o)
| Management component | Description |
|---|---|
| Psychological therapy | 1st line: anorexia-nervosa-focused family therapy
Alternative (if anorexia-nervosa-focused family therapy is not appropriate)
|
| Dietary advice / support |
|
| Ongoing physical health monitoring | Risk-based physical monitoring (applicable for all eating disorders):
Patients with anorexia nervosa should have at least annual reviews that check:
Other assessment:
|
| Identifying and treating comorbidities | Including:
|
Adults
| Management component | Description |
|---|---|
| Psychological therapy | 1st line: consider ANY of the following psychological therapies
Alternative (if all 3 of the above are not appropriate)
|
| Dietary advice / support | Age-appropriate oral multivitamin and multimineral supplement until dietary intake is sufficient to meet recommended nutritional requirements |
| Ongoing physical health monitoring | Risk-based physical monitoring (applicable for all eating disorders):
Patients with anorexia nervosa should have at least annual reviews that check:
Consider bone mineral density assessment (DEXA) after 2 years of being underweight or earlier if they experience bone pain or recurrent fractures) |
| Identifying and treating comorbidities | Including:
|