Key Facts

Bulimia nervosa involves cycles of binge eating and compensatory purging behaviours. Unlike anorexia, weight is often normal, which may delay recognition.

Epidemiology

Prevalence ~1-2%; F:M ~10:1. Peak onset 18-25 years. Higher prevalence in Western countries. Often hidden due to shame — average delay to treatment ~5 years.

Aetiology

• Genetic: Heritability ~55-60%; shared genetic risk with AN and other psychiatric disorders
• Cognitive: Overvaluation of shape/weight, dichotomous thinking, dietary restraint → binge → purge cycle
• Neurobiological: Serotonergic dysfunction, altered reward pathways, impaired satiety signals
• Environmental: Dieting, media pressure, peer influences, childhood adversity

Pathophysiology

• Restrict-binge-purge cycle: Dietary restraint → physiological and psychological deprivation → binge eating → guilt/disgust → compensatory purging → temporary relief → continued restriction
• Vomiting: Hypokalaemic metabolic alkalosis; dental erosion; Mallory-Weiss tears; parotid hypertrophy
• Laxative abuse: Metabolic acidosis, dehydration, chronic constipation (lazy bowel)
• Ipecac abuse: Cardiomyopathy (rare but potentially fatal)

Core Features

• Recurrent binge eating: Large amounts in short time, sense of loss of control
• Compensatory behaviours: Self-induced vomiting, laxative/diuretic abuse, excessive exercise, fasting
• Self-evaluation excessively influenced by body shape and weight
• Normal or near-normal weight

Physical Signs

• Russell's sign (calluses on knuckles)
• Parotid gland enlargement ('chipmunk cheeks')
• Dental erosion (perimolysis — especially lingual surfaces of upper teeth)
• Periorbital petechiae (forceful vomiting)
• Oedema (fluid shifts)

Red Flags

• Severe hypokalaemia (<2.5 mmol/L) — cardiac arrhythmia risk
• Haematemesis — Mallory-Weiss tear or Boerhaave syndrome
• Syncope, palpitations — cardiac complications
• Suicidal ideation — elevated risk

Bedside

• BMI: Usually normal (18.5-30)
• Vital signs: HR, BP (postural drop if dehydrated)
• ECG: QTc prolongation, U waves (hypokalaemia)
• Dental examination: Erosion pattern

Bloods

• U&Es: Hypokalaemia, hyponatraemia, raised urea (dehydration)
• Bicarbonate: Elevated (metabolic alkalosis from vomiting) or low (laxative abuse)
• Amylase: Raised (salivary, from vomiting)
• FBC, LFTs, TFTs: Baseline
• Phosphate, Mg²⁺: Electrolyte status

Special Tests

• EDE-Q: Eating disorder severity assessment
• SCOFF questionnaire: Screening

Non-pharmacological (NICE NG69)

• Step 1: Guided self-help based on CBT (4-9 sessions over 16 weeks)
• Step 2: CBT-BN (16-20 sessions) — first-line definitive treatment; ~50% achieve abstinence from binge-purge behaviours
• Alternative: Interpersonal therapy (IPT) if CBT not effective
• Dietary guidance: Regular eating pattern (3 meals + 2-3 snacks), avoid dietary restriction

Pharmacological

• Fluoxetine 60mg OD: Recommended alongside or after CBT; reduces binge-purge frequency by ~50%
• Higher dose than for depression (60mg vs 20mg)
• Other SSRIs have less evidence
• Not recommended: TCAs (cardiac risk), MAOIs

Referral Criteria

• Suspected bulimia — specialist eating disorder service
• Medical complications — medical assessment
• Failed guided self-help — step up to specialist CBT-BN
• Severe electrolyte disturbance — urgent medical admission

• CBT-BN: ~50% achieve remission; ~30% partial improvement; ~20% chronic course
• Better prognosis than anorexia nervosa; lower mortality (SMR ~2×)
• Recovery: ~50-70% recover with treatment; relapse common (30-50%)
• Suicide: Elevated risk but lower than AN
• Good prognostic factors: Shorter duration, earlier treatment, absence of comorbid personality disorder
• Long-term dental damage may be permanent
• Medical complications generally reversible with cessation of purging

Electrolyte Patterns in Purging