Anorexia Nervosa

Anorexia nervosa is a serious psychiatric disorder. It is characterised by persistent restriction of energy intake leading to significantly low body weight. Patients have an intense fear of weight gain, or persistent behaviour interfering with weight gain despite low weight, and a disturbance in how body weight or shape is experienced.

It carries the highest mortality rate of any psychiatric disorder. This reflects both the direct medical complications of severe malnutrition and the significant associated suicide risk.

Diagnosis and management require careful integration of medical risk assessment and stabilisation with specific, evidence based psychological treatment addressing the underlying cognitive and behavioural disturbance.

Pathophysiology

• Sustained, severe caloric restriction relative to metabolic requirement produces a hypometabolic adaptive state. Lean body mass and fat mass are lost progressively.
• Loss of lean mass includes, critically, cardiac muscle mass. This contributes directly to the characteristic bradycardia and hypotension and, in the most severe cases, an increased risk of potentially fatal arrhythmia.
• Widespread endocrine and metabolic disturbance follows. This includes hypothalamic suppression of the reproductive axis (producing amenorrhoea), reduced bone density, and impaired thermoregulation. Reduced bone density reflects the combined effect of oestrogen deficiency and direct nutritional deprivation on bone metabolism.
• The severity and duration of malnutrition correlate directly with the extent of physiological adaptation and medical risk.
• Refeeding syndrome risk on nutritional rehabilitation reflects severe, chronic malnutrition and profound depletion of total body phosphate, potassium and magnesium. These parameters frequently appear deceptively normal on standard blood testing in the still malnourished, pre-refeeding state.

• The core diagnostic features are significant, sustained low body weight relative to the individual's expected weight trajectory, intense fear of weight gain, and disturbed body image. Individuals frequently perceive themselves as overweight or of normal weight despite objective, often severe, underweight status.
• The restrictive subtype presents with caloric restriction, often accompanied by excessive exercise, without regular binge eating or purging behaviour.
• The binge purge subtype shares features with bulimia nervosa but occurs in the context of significantly low body weight. This is an important distinguishing feature between these two related conditions.
• Medical complications reflect the direct consequences of severe malnutrition:
  • Bradycardia, a common, expected physiological adaptation to reduced metabolic demand, though it also carries specific arrhythmia risk in severe cases.
  • Hypotension, hypothermia, and amenorrhoea.
  • Lanugo hair growth (fine, downy hair reflecting a physiological thermoregulatory adaptation).
  • Significant reduction in bone density with associated fracture risk.
  • In the most severe cases, multi-organ dysfunction reflecting the extent of physiological compromise.
• Denial or minimisation of severity, with significant ambivalence or active resistance toward treatment, is a characteristic and clinically important feature. It frequently complicates engagement with medical and psychological assessment and treatment.
• This requires a particularly careful, collaborative, non-confrontational therapeutic approach.

• Diagnosis is established through a full clinical assessment, following the general principles detailed under eating disorders. It incorporates weight history and trajectory, detailed exploration of eating behaviour and associated cognitions regarding weight and shape, and assessment of any associated compensatory or purging behaviour.
• Full medical risk assessment is an essential component of every assessment. It includes:
  • Vital signs, specifically heart rate and postural blood pressure.
  • Weight and body mass index, interpreted in the context of the individual's expected weight trajectory and growth curve where relevant. In children and adolescents, standard adult body mass index thresholds are not directly applicable.
  • Electrocardiography, assessing specifically for bradycardia and for corrected QT interval prolongation given the associated arrhythmia risk.
  • Blood testing: full blood count, electrolytes including phosphate and magnesium, renal and liver function, and glucose.
• Structured medical risk stratification tools formally categorise risk level and directly guide the urgency and setting of subsequent intervention.
• Bone density assessment (dual energy x ray absorptiometry) is appropriate where amenorrhoea has been sustained for a significant period. Prolonged oestrogen deficiency and nutritional compromise carry a risk of clinically significant bone density reduction.
• Denial or minimisation is frequently present. Corroborative history from family members or other close contacts, where the patient consents, can give valuable additional information on the true extent and duration of the eating disturbance.

• Medical stabilisation takes priority where structured assessment identifies significant medical risk.
• Inpatient admission is indicated for severe bradycardia, significant hypotension, significant electrolyte disturbance, very low body mass index, or other markers of high acute medical risk. The setting, a medical or specialist eating disorder unit, depends on severity and local service configuration.
• Nutritional rehabilitation is guided by specialist dietetic input. In significantly malnourished patients, reintroduce calories carefully and gradually, given the critical risk of refeeding syndrome, addressed in full detail under that specific condition.
• Structured monitoring of phosphate, potassium and magnesium is essential throughout the early refeeding period. Add cardiac monitoring where indicated by the severity of the presentation.
• Family based treatment is the first line, most strongly evidence supported psychological treatment for adolescents with anorexia nervosa. It empowers parents or carers to take an active, structured role in supporting nutritional rehabilitation and normalisation of eating behaviour.
• In this younger population, family based treatment has substantially stronger evidence than individual therapy approaches used in isolation.
• Specific evidence based individual psychological therapies are appropriate for adults. These include cognitive behavioural therapy adapted for eating disorders and the Maudsley model of anorexia nervosa treatment for adults.
• Treatment is typically prolonged, reflecting the frequently chronic, relapsing and remitting natural history. It requires sustained, patient, collaborative engagement given the characteristic ambivalence toward treatment and recovery.
• Pharmacological treatment has a limited, generally adjunctive role in anorexia nervosa, as no medication has been shown to directly and substantially improve the core eating disorder psychopathology.
• Consider antidepressant or other psychotropic medication where a significant coexisting depressive or anxiety disorder is present, following standard principles for that condition. It is not a primary treatment for the anorexia nervosa itself.
• Ongoing, coordinated multidisciplinary management integrates medical monitoring (including regular weight, vital signs and, where indicated, biochemical monitoring), nutritional support, and specialist psychological treatment. It requires careful, longitudinal engagement given the frequently prolonged, relapsing course and the substantial associated mortality risk.
• Early recognition and intervention, particularly in younger patients, are associated with improved long term outcome. Keep a low threshold for specialist referral and assessment where the diagnosis is suspected.