Eating Disorders and Somatic Symptom Disorders

Eating disorders carry the highest mortality of any psychiatric condition. Anorexia nervosa (AN) is characterised by persistent restriction of energy intake leading to a significantly low body weight (BMI <17.5 kg/m² in adults, or <85% of expected weight in children), intense fear of weight gain, and distorted body image. AN is further classified as restricting type or binge-eating/purging type. Medical complications of AN are pervasive and can be life-threatening, including: cardiovascular (bradycardia, QT prolongation increasing arrhythmia risk, mitral valve prolapse, hypotension), metabolic (hypoglycaemia, electrolyte disturbances, osteoporosis from oestrogen deficiency), haematological (leukopenia, anaemia), and endocrine (hypothalamic amenorrhoea, low thyroid function).

Refeeding syndrome is a critical complication of nutritional rehabilitation in severe AN (and other malnourished states). Rapid reintroduction of carbohydrates causes a sudden shift of phosphate, potassium, and magnesium from extracellular to intracellular compartments, precipitating potentially fatal hypophosphataemia, cardiac arrhythmias, and respiratory failure. Management requires careful monitoring and supplementation of electrolytes and thiamine (Pabrinex) during refeeding, which should be initiated at low caloric levels and escalated slowly.

In NZ, compulsory treatment for anorexia nervosa can be invoked under the Mental Health (Compulsory Assessment and Treatment) Act 1992 when the patient's life is at immediate risk from their eating disorder and voluntary treatment has failed. This is used cautiously and requires involvement of a psychiatrist and often a judge in disputed cases.

Bulimia nervosa (BN) is characterised by recurrent binge eating followed by compensatory behaviours (self-induced vomiting, laxative misuse, excessive exercise). Russell's sign — callosities or abrasions on the dorsum of the hand from repeated self-induced vomiting — is a classic examination finding. Electrolyte disturbances in BN include hypokalaemia, hyponatraemia, and metabolic alkalosis from vomiting. Treatment: CBT-Enhanced (CBT-E) is the evidence-based psychological treatment.

Somatic symptom disorder involves persistent physical symptoms causing significant distress or impairment, with excessive thoughts, feelings, or behaviours related to the symptoms. Illness anxiety disorder is marked by preoccupation with having or acquiring a serious illness with minimal or no somatic symptoms. Conversion disorder (functional neurological symptom disorder — FND) involves neurological symptoms (weakness, paralysis, non-epileptic seizures, sensory loss) unexplained by neurological disease. Positive signs on examination (e.g., Hoover sign for functional leg weakness, variability with distraction) support the diagnosis. FND is not malingering — symptoms are real, involuntary, and distressing. A positive diagnosis approach (rather than diagnosis by exclusion) is recommended.