Core diagnostic features

• Persistent restriction of energy intake leading to significantly low body weight for age, sex and developmental trajectory.
• Intense fear of gaining weight or persistent behaviour that interferes with weight gain.
• Disturbance in self‑perceived weight or shape, undue influence of weight on self‑evaluation, or lack of recognition of seriousness of low body weight.
• Specify: restricting type vs binge‑eating/purging type; severity by BMI or clinical risk.

Medical risks & complications

• Cardiovascular: bradycardia, hypotension, arrhythmias, reduced cardiac output.
• Metabolic & endocrine: electrolyte disturbances, hypoglycaemia, hypothalamic amenorrhoea, low bone density.
• Gastrointestinal: delayed gastric emptying, constipation, liver enzyme abnormalities.
• Neurological & cognitive: concentration problems, peripheral neuropathy, risk of refeeding syndrome during renutrition.
• High suicide risk; monitor for self‑harm and psychiatric comorbidity (depression, anxiety, OCD).

Assessment checklist

1. Medical evaluation: weight, height, BMI, orthostatics, ECG (bradycardia, QT prolongation), electrolytes, renal & liver function, glucose, magnesium, phosphate, calcium, thyroid function, and pregnancy test when applicable.
2. Psychiatric assessment: duration of illness, eating behaviours, exercise, purging, suicidality, motive for restriction, cognitive rigidity and family dynamics.
3. Nutritional assessment: recent weight loss rate, caloric intake, dietary pattern, micronutrient deficiencies and dependence on supplements or laxatives.
4. Functional assessment: school/work performance, social isolation, and ability to attend outpatient therapy.

When to admit — medical & psychiatric indications

• Medical instability: severe bradycardia (HR <40–50 bpm depending on age/context), syncope, hypotension, arrhythmia, electrolyte abnormalities requiring correction, severe dehydration, or rapid weight loss compromising function.
• High risk features: BMI very low (varies by guideline), failure of outpatient renutrition, severe psychiatric risk (suicidality, severe self‑harm), or inability to engage in treatment.
• Consider admission for medical stabilization, refeeding with monitoring, and initiation of multidisciplinary treatment when indicated.

Treatment framework — multidisciplinary & stepped care

• Multidisciplinary team: psychiatry/psychology, dietitian, medical physician (adolescent/physical health), nursing, family therapist and social work — coordinated care improves outcomes.
• Stepped care: outpatient evidence‑based psychotherapy for mild–moderate cases; day‑programmes for moderate–severe or poor outpatient progress; inpatient care for medical instability or high psychiatric risk.
• Set collaborative goals: weight restoration targets, behavioural goals (regular eating), reduction of compensatory behaviours, and psychosocial recovery.

Evidence‑based psychotherapies

• Family‑Based Treatment (FBT): first‑line for adolescents — empowers families to re‑establish eating, gradually return control to the adolescent, and address family interactions that maintain restriction.
• Cognitive Behavioural Therapy — Enhanced (CBT‑E): effective for adults and older adolescents focusing on eating disorder psychopathology, perfectionism, low self‑esteem and interpersonal maintenance factors.
• MANTRA (Maudsley Anorexia Nervosa Treatment for Adults): a formulation‑driven therapy addressing cognitive, emotional and relational maintaining factors in adults with AN.
• Specialist supportive clinical management (SSCM): combines clinical management with supportive therapy; used in trials and as comparator treatment but can be part of pragmatic care.

Nutritional rehabilitation & refeeding

• Aim for gradual, monitored weight restoration with regular meals and structured plans; individualised caloric targets, often starting higher than historically recommended to reduce prolongation of malnutrition.
• Monitor for refeeding syndrome: check electrolytes (phosphate, potassium, magnesium), supplement phosphate proactively where high risk, and replace electrolytes promptly.
• Oral refeeding preferred; use supplements or enteral feeding when oral intake inadequate or in severe cases—carefully coordinate transition from tube feeds to oral intake to avoid dependence.

Pharmacologic treatments — adjunctive role

• No medication reverses core AN psychopathology. Use adjunctively for comorbid conditions (SSRIs for depression/anxiety after weight restored) and target acute symptoms (antipsychotics like olanzapine may aid weight gain and reduce cognitive rigidity in some adults—but monitor metabolic effects).
• Zinc supplementation can assist weight restoration in some studies; correct micronutrient deficiencies as needed.

When to refer & follow‑up

• Refer urgently for medical instability, severe malnutrition, rapid weight loss, arrhythmia, syncope, or high suicide risk.
• Early involvement of specialist eating‑disorder services, dietitians and family therapists improves outcomes; plan long‑term follow‑up for relapse prevention and bone health monitoring.

Key takeaways

• Anorexia nervosa is a high‑risk disorder requiring early multidisciplinary assessment, medical safety planning and evidence‑based psychotherapeutic interventions (FBT in adolescents, CBT‑E/MANTRA in adults).
• Nutritional rehabilitation with careful monitoring for refeeding syndrome is central—coordinate medical, psychiatric and dietetic care and involve families where appropriate.
• Monitor for suicidal ideation, comorbidity and long‑term complications (bone health, cardiac) and provide continuity of care to reduce relapse risk.