Eating disorders appear in Paper B as part of general adult psychiatry and feeding and eating disorders under ICD-11. The conditions tested are anorexia nervosa (including its medical complications), bulimia nervosa, and binge-eating disorder. Recall questions confirm that specific electrolyte disturbances, refeeding risks, and treatment approaches for adolescents are recurring themes.
ICD-11 Diagnostic Criteria
Anorexia nervosa: Significantly low body weight (BMI below 18.5 in adults, or below the 5th percentile in children/adolescents) that is less than minimal expected for the individual’s age, sex, and developmental trajectory. The weight loss is caused by restricted energy intake relative to energy requirements. There is an intense fear of weight gain or persistent behaviour that prevents weight gain, and body image disturbance (weight or shape overvalued in self-evaluation, or persistent lack of recognition of the seriousness of the low weight). Anorexia may be restricting type (weight loss primarily through dieting/fasting) or binge-purge type (regular binge eating or purging behaviours). The ICD-11 removed the requirement for amenorrhea (which was in ICD-10). The BMI thresholds for severity: mild (BMI 17-18.5), moderate (16-17), severe (15-16), extreme (less than 15).
Bulimia nervosa: Recurrent episodes of binge eating (eating an abnormally large amount of food in a discrete period with a sense of loss of control) occurring at least once per week for at least 1 month. Recurrent compensatory behaviours to prevent weight gain (vomiting, laxatives, diuretics, fasting, excessive exercise). Self-evaluation is unduly influenced by weight and shape. In contrast to anorexia, weight is usually within the normal range or overweight.
Binge-eating disorder: Recurrent binge eating (as above) WITHOUT regular compensatory behaviours. Binge-eating episodes are associated with eating more rapidly than normal, eating until uncomfortably full, eating large amounts when not hungry, eating alone because of embarrassment, and feeling disgusted, depressed, or guilty afterwards. Distress about binge eating is required. Occurs at least once per week for 3 months.
Exam pattern — prevalence: A recall question tested comparisons of prevalence. The key facts: bulimia nervosa is more common than anorexia nervosa. Lifetime prevalence: anorexia ~0.5-1%, bulimia ~1-2%, binge-eating disorder ~2-3%. All eating disorders are increasing in prevalence across developed countries.
Medical Complications (High-Yield for Recall Questions)
Anorexia nervosa: The most concerning electrolyte abnormality is hypokalaemia (especially in the binge-purge subtype). ECG findings in hypokalaemia: U waves, prolonged QT, T wave inversion, ST depression. A recall question: “Anorexic girl, abusing diuretics and laxatives, presents with lethargy and muscle cramps — likely ECG finding?” Answer: hypokalaemia-related ECG changes (U waves, long PR). Other complications: bradycardia, hypotension, osteoporosis, delayed gastric emptying, constipation, hypothermia, lanugo hair, salivary gland hypertrophy (from vomiting), dental erosion (perimolysis), Russell’s sign (knuckle calluses from self-induced vomiting), refeeding syndrome (hypophosphataemia, hypokalaemia, hypomagnesaemia, fluid shifts, cardiac arrhythmia) when nutrition is reintroduced too aggressively.
Bulimia nervosa: Hypokalaemia from vomiting or laxative use is the most dangerous complication. Calluses on knuckles (Russell’s sign), salivary gland hypertrophy (parotid enlargement), dental erosion, oesophageal tears (Mallory-Weiss syndrome), and aspiration pneumonitis. Unlike anorexia, the BMI is normal or elevated, so medical complications may be overlooked.
Refeeding syndrome: Occurs within 4 days of reintroducing nutrition after a period of starvation. The hallmark is hypophosphataemia (phosphate moves from serum into cells during refeeding). Other features: hypokalaemia, hypomagnesaemia, fluid overload, cardiac arrhythmia, delirium, seizures, and death. Prevention: start refeeding at low calorie levels (5-10 kcal/kg/day for the first 3-5 days), monitor phosphate, potassium, magnesium daily, and replace electrolytes aggressively. NICE guidance for inpatient refeeding. This is a high-yield exam topic.
NICE Treatment Guidelines (NG69)
Anorexia nervosa: Psychological therapy is first-line. For adolescents, family therapy (specifically the Maudsley model, involving parents in refeeding) is the first-line psychological treatment. This is a high-yield distinction from bulimia, where individual CBT is first-line. For adults, CBT-ED (adapted for eating disorders), focal psychodynamic therapy, and cognitive analytic therapy have evidence. Weight restoration is the primary goal in the underweight patient. No medication is licensed for anorexia specifically. Olanzapine has some evidence for promoting weight gain and reducing anorexic cognitions but is not first-line. There is strong evidence that SSRIs are NOT effective in the underweight anorexic patient — they become effective only after weight restoration.
Bulimia nervosa: CBT-ED (16-20 sessions) is first-line. SSRI medication (fluoxetine 60mg is the only licensed dose for bulimia) is an alternative or adjunct. The high dose (60mg) is specific to bulimia and differs from the depression dose. SSRIs are more effective than placebo for reducing binge eating and purging, with an approximately 60% reduction in binge frequency. Combined treatment (CBT-ED + SSRI) is no more effective than CBT-ED alone for long-term outcomes.
Binge-eating disorder: CBT-ED is first-line. Self-help approaches (guided CBT-based self-help) can be effective for less severe cases. Lisdexamfetamine has evidence for reducing binge frequency and is licensed in some jurisdictions (USA) but not routinely in the UK.
Prognosis and Mortality
Anorexia nervosa has the highest mortality rate of any psychiatric disorder (standardised mortality ratio approximately 5-6). Death is from medical complications (starvation, electrolyte disturbance) or suicide. The crude mortality rate is about 5-10% over 10-20 years. Bulimia has a lower mortality rate (SMR approximately 2). Recovery rates: approximately 50% of anorexia patients recover completely, 30% improve partially, 20% have a chronic illness trajectory. For bulimia, recovery rates are higher (approximately 60-70% with treatment). Suicide risk is elevated in all eating disorders but highest in anorexia.
High-Yield Recall Patterns
- Most concerning electrolyte disturbance in anorexia: Potassium (hypokalaemia) — risk of cardiac arrhythmia. NOT bicarbonate, phosphate alone
- ECG finding in laxative/diuretic abuse + anorexia: U waves, long PR, T inversion (hypokalaemia)
- Adolescent anorexia first-line treatment: Family therapy (Maudsley model)
- Bulimia first-line treatment: CBT-ED (16-20 sessions). SSRI fluoxetine 60mg is alternative.
- Fluoxetine dose for bulimia: 60mg (not 20mg, not 40mg)
- SSRIs in underweight anorexia: NOT effective until weight restored
- Refeeding syndrome key marker: Hypophosphataemia — start refeeding at 5-10 kcal/kg/day
- Russell’s sign: Knuckle calluses from self-induced vomiting (bulimia, anorexia binge-purge type)
- Salivary gland enlargement: Parotid hypertrophy from vomiting (bulimia)
- Highest mortality psychiatric disorder: Anorexia nervosa (SMR 5-6)
- Bulimia more common than anorexia: Yes. And all EDs increasing across developed countries.
- Binge-eating disorder vs bulimia: BED has NO regular compensatory behaviours. This is the key distinction.
PsychStar’s Paper B question bank covers eating disorders with questions calibrated to real exam difficulty. Start with 5 free questions at psychstar.io/try.