Psychiatry - eating disorders

Description

Disorder	Core feature	Weight
Anorexia nervosa	Restriction -> significantly low weight + intense fear of weight gain + body image disturbance	Low
Bulimia nervosa	Binge eating + compensatory behaviour (vomiting, laxatives, exercise, fasting), >=1/week for 3 months	Normal or above
Binge eating disorder	Binges without compensation; the commonest eating disorder	Often overweight/obese
ARFID	Avoidant/restrictive intake without body image disturbance	Low or normal
OSFED	Subthreshold or atypical (incl. atypical anorexia - full cognitive picture at normal weight)	Any

Anorexia subtypes: restricting vs binge-eating/purging
DSM-5 removed the amenorrhoea criterion and specific BMI cut-offs. Physical severity is not proportional to weight - atypical anorexia carries the same medical risk

~1 million Australians (~4%) have an eating disorder at any time
Anorexia lifetime prevalence ~1-4% in women, ~0.3% in men; bulimia ~1-2%; binge eating disorder ~2-4% - the commonest
F:M ~3:1 overall (previously quoted as 10:1 - male disease is substantially under-recognised)
Peak onset 15-25 years; incidence rising, and onset age falling
Elevated in athletes, dancers, models, jockeys, and in type 1 diabetes

Multifactorial: heritability 50-60% for anorexia
GWAS reclassifies anorexia as a metabo-psychiatric disorder - loci overlap with insulin sensitivity, BMI and lipid metabolism as well as with OCD, depression and schizophrenia
Personality: perfectionism, harm avoidance, obsessionality (anorexia); impulsivity and affective instability (bulimia)
Triggers: dieting, puberty, adversity, sport, bullying, social media
Starvation itself produces and perpetuates much of the psychopathology - rigidity, preoccupation with food, low mood, social withdrawal (Minnesota Starvation Experiment)
- -> weight restoration is a prerequisite for psychological therapy to work, not a consequence of it
Type 1 diabetes: insulin omission for weight control ("diabulimia") - very high morbidity

Screen actively. Patients conceal, and normal weight does not exclude.

Screening

SCOFF questionnaire (>=2 positive is a screen positive), EDE-Q
Ask about: weight history and rate of loss, dietary restriction, binge episodes, vomiting, laxative/diuretic use, exercise compulsion, insulin omission, body image, menstrual history

Examination

Weight, height, BMI; growth chart and expected weight in adolescents
Vital signs: bradycardia, hypotension, postural drop, hypothermia
Sit-up-squat-stand (SUSS) test for proximal myopathy
Signs of purging: Russell sign (knuckle callus), dental erosion, parotid hypertrophy, subconjunctival haemorrhage
Lanugo hair, dry skin, acrocyanosis, peripheral oedema, hair loss

Investigations

UEC (hypokalaemia, hypochloraemic metabolic alkalosis with vomiting; hypophosphataemia), magnesium, phosphate, calcium, glucose
FBE (pancytopenia from marrow gelatinous transformation), LFT (transaminitis in starvation), albumin, CK
ECG - bradycardia, prolonged QTc, arrhythmia
TSH (low T3 syndrome - do not treat), LH/FSH/oestradiol
DEXA if amenorrhoeic >6-12 months
Normal bloods do not indicate medical stability - a patient can arrest with a normal potassium

Medical instability - admission criteria

HR <40 (or <50 with symptoms), SBP <80, postural drop >20 mmHg or HR rise >20
Temperature <35.5C
K+ <3.0, Na+ <125, PO4 or Mg low, glucose <3.0
BMI <14, or rapid weight loss >1 kg/week sustained
QTc >450 ms, arrhythmia
Suicidality, failure of outpatient management, acute food refusal

A. Medical stabilisation and refeeding

Refeeding syndrome is the acute killer - occurs in the first 5-7 days of refeeding
- Mechanism: carbohydrate load -> insulin surge -> intracellular shift of phosphate, potassium and magnesium in a depleted patient
- -> hypophosphataemia -> cardiac failure, arrhythmia, rhabdomyolysis, seizures, death
- Highest risk: BMI <14, minimal intake >5 days, prior low phosphate, alcohol use
Prevention
- Thiamine 100 mg (and B vitamins) BEFORE any carbohydrate
- Start at a modest calorie level and increase gradually, with daily electrolytes
- Monitor phosphate, potassium and magnesium daily for at least the first week and replace aggressively
- Guidance has shifted from "start low, go slow" to more rapid refeeding under close biochemical monitoring in supervised units - underfeeding causes its own harm
Nasogastric feeding where oral intake is inadequate; may require involuntary treatment under the relevant Mental Health Act

B. Psychological therapy - the definitive treatment

Disorder	First-line
Anorexia - adolescent	Family-based treatment (Maudsley) - the strongest evidence in adolescents
Anorexia - adult	CBT-E, MANTRA, or SSCM
Bulimia	CBT-E first-line
Binge eating disorder	CBT-E; guided self-help

C. Pharmacotherapy - adjunctive only

*No medication has established efficacy for the core features of anorexia nervosa*
- Olanzapine produces modest weight gain but does not change psychopathology
- SSRIs are ineffective in the starved state - the brain is too depleted for them to work; treat comorbid depression after weight restoration
Bulimia: fluoxetine 60 mg - the one licensed indication, and a higher dose than for depression
Binge eating disorder: lisdexamfetamine (restricted availability in Australia), SSRI
Manage constipation, osteoporosis (oestrogen replacement or transdermal oestradiol in adolescents; bisphosphonates rarely), and dental care

D. Multidisciplinary and long-term

Physician + psychiatrist + dietitian + psychologist, with family involvement - single-clinician management fails
Australian: Eating Disorder Plan (MBS) provides up to 40 psychological and 20 dietetic sessions per year
Weight restoration and menstrual return are the two most reliable markers of recovery
Avoid weighing at home; blind weighing where clinically appropriate

Depression, anxiety, OCD, PTSD, personality disorder
Substance use disorder (bulimia > anorexia)
Self-harm and suicide
Type 1 diabetes with insulin omission
Osteoporosis and fragility fracture - often irreversible if it occurs in adolescence
Infertility, pregnancy complications
Superior mesenteric artery syndrome, gastroparesis, constipation
Cardiac: bradycardia, prolonged QTc, mitral valve prolapse, pericardial effusion, cardiomyopathy (ipecac)
Dental erosion, oesophagitis, Mallory-Weiss tear, Boerhaave

Outcome in anorexia nervosa

Roughly 50% full recovery, 30% partial, 20% chronic
Standardised mortality ratio ~5-6x - the highest of any psychiatric disorder
- Deaths from medical complications and suicide in roughly equal measure
Poor prognostic factors
- Low BMI at presentation - among the strongest predictors of poor long-term outcome
- Long duration before treatment, purging subtype, adult (vs adolescent) onset, comorbid substance use or personality disorder, poor family functioning
Adolescent onset with early family-based treatment has the best outcome - duration of untreated illness is the key modifiable factor

Bulimia and binge eating disorder

Monitor

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