Mental Health

Anorexia nervosa

An eating disorder in which restriction driven by fear of weight gain and disturbed body image causes significantly low weight, starvation physiology and potentially life-threatening medical instability.

In a nutshell

Anorexia nervosa is restriction driven by fear of weight gain and disturbed body image, leading to significantly low weight and starvation physiology. Medical risk is determined by the whole picture, not BMI alone. Stabilise severe physical risk, refeed through a trained protocol with electrolyte monitoring, and provide specialist psychological therapy alongside family or carer support where appropriate.

Classic presentation

A person with progressive restriction, weight and shape preoccupation, fear of weight gain, cold intolerance, fatigue, dizziness or amenorrhoea, with bradycardia or postural symptoms and possible denial of the seriousness of the low weight.

Key points

Anorexia nervosa can occur at any age and in any sex; do not let a non-stereotypical body size or presentation delay referral.
Bradycardia, hypotension, hypothermia, hypoglycaemia, electrolyte disturbance, QT prolongation, syncope and rapid weight loss are medical-risk findings.
Do not use BMI or a single weight threshold alone to decide severity, admission or access to treatment.
Refeeding syndrome can emerge after nutrition starts, so use a trained local protocol with thiamine, serial electrolytes and prompt replacement.
Adults may be offered CBT-ED, MANTRA or specialist supportive clinical management; children and young people are usually offered family-based treatment first.
Medication is not sole treatment for anorexia; psychological therapy, nutritional rehabilitation and physical monitoring are the core treatment.
Suicide risk, self-harm, safeguarding, pregnancy, diabetes and comorbid illness must be assessed alongside starvation.

First-line investigation

Weight and trajectory, pulse, blood pressure, temperature and hydration assessment, ECG, and bloods including glucose, renal function, potassium, phosphate and magnesium, interpreted with the eating-disorder and psychiatric assessment.

Management

Recognise and refer early

Ask directly about restriction, weight and shape concerns, purging, exercise, self-harm and suicide, and refer promptly to specialist eating-disorder care.^1,3,5

Grade medical risk and choose the setting

Assess weight trajectory, vital signs, ECG, glucose and electrolytes; use the full clinical picture rather than BMI alone, and escalate severe compromise to medical or day-patient stabilisation.^1,3

Restore nutrition safely

Use a trained refeeding SOP with dietetic support, thiamine and serial electrolyte monitoring; replace potassium, phosphate or magnesium promptly according to local guidance.^1,3,6

Deliver specialist psychological treatment

Offer adults CBT-ED, MANTRA or SSCM; offer children and young people anorexia-focused family therapy first, with specialist alternatives when needed.^1,4,2

Manage comorbidity and legal or safeguarding risk

Assess suicidality, self-harm, pregnancy, diabetes, substance use, bone health, capacity and safeguarding; seek senior advice if refusal creates serious physical risk.^1,3,7

Plan shared recovery and relapse prevention

Agree physical, nutritional and psychological goals, family or carer involvement, emergency contacts, transition arrangements and early warning signs in a shared care plan.^1,2,7

Exam traps

Amenorrhoea is associated with anorexia but is not required for diagnosis.
Normal baseline electrolytes do not eliminate refeeding risk; values may fall after nutrition is restored.
A normal or higher weight does not exclude an eating disorder, and a low BMI is not by itself an admission rule.
A meal plan alone does not treat anorexia; it must be integrated with specialist psychological therapy.
Compulsory treatment is a last resort for serious risk when safe treatment cannot otherwise be delivered, not a routine response to ambivalence.

Illustrations

Starvation-driven organ downregulationDiagram showing how inadequate energy intake affects cardiovascular, endocrine, thermoregulatory and musculoskeletal systems, linking physical signs to starvation physiology.PassFinals · original

Refeeding syndrome mechanismSchematic of nutritional restoration causing insulin-mediated intracellular electrolyte shifts in a malnourished patient, with monitoring and replacement points.PassFinals · original

Starvation and eating-disorder cognitionDiagram showing how starvation can worsen rigidity, anxiety and preoccupation, reinforcing restriction and the need to combine nutritional rehabilitation with specialist psychological therapy.PassFinals · original

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.