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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
Key points
- Significantly low weight + fear of weight gain/behavior preventing gain + body image disturbance
- Subtypes: restricting and binge-eating/purging
- Medical instability drives admission: bradycardia, hypotension, hypothermia, electrolytes, arrhythmia, syncope, dehydration
- Refeeding syndrome causes hypophosphatemia, hypokalemia, hypomagnesemia, cardiac risk
- Treatment is nutritional rehabilitation plus eating-disorder-focused psychotherapy; family-based treatment for adolescents
Overview
Anorexia nervosa involves restrictive intake leading to significantly low body weight, intense fear of gaining weight, and body image disturbance or denial of seriousness. Amenorrhea is common but no longer required.
Epidemiology
Onset is usually adolescence/young adulthood. Risks include family history, perfectionism, anxiety/OCD traits, dieting, weight stigma, trauma, and sports emphasizing leanness. Mortality is high from medical complications and suicide.
Clinical Features
Symptoms
Severe restriction, calorie counting, fasting, food avoidance
Fear of weight gain despite low weight
Body checking, distorted body image, overexercise
Cold intolerance, constipation, dizziness, amenorrhea/low libido
Syncope, chest pain, palpitations, severe weakness, suicidality
Signs
Low BMI or significant weight loss
Bradycardia, hypotension, orthostasis, hypothermia
Lanugo, dry skin, hair loss, acrocyanosis, edema
Arrhythmia, dehydration, confusion, severe wasting
Investigations
First-line
Vitals/weight trajectoryOrthostatics, BMI/expected body weight, rate of loss
LabsCMP, Mg, phosphate, CBC, glucose, LFTs, TSH if indicated, urinalysis, pregnancy
ECGBradycardia, QT prolongation, arrhythmias
Second-line
Bone healthDXA if prolonged low weight/amenorrhea/fracture risk
Eating disorder assessmentRestriction, binge/purge, laxatives/diuretics, exercise, body image, suicide
Refeeding monitoringFrequent phosphate, potassium, magnesium, glucose
Specialist
Medical admission/eating disorder unitUnstable vitals, severe malnutrition, electrolytes, arrhythmia, syncope, dehydration, food refusal, suicidality
Specialist teamPsychiatry, dietitian, medical physician, therapy, family
1
Medical stabilization
- Admit for unstable vitals, arrhythmia, electrolytes, syncope, severe dehydration, or food refusal
- Correct hypoglycemia, hypothermia, dehydration, and electrolytes carefully
- Monitor ECG and refeeding labs
2
Nutrition/psychotherapy
- Structured meals and monitored weight restoration
- Prevent refeeding syndrome with careful advancement and phosphate/Mg/K monitoring
- Adolescents: family-based treatment; adults: eating-disorder-focused CBT or specialist psychotherapy
3
Medication
- No medication reliably restores weight as primary treatment
- Olanzapine may help weight/anxiety in selected patients
- Treat depression/anxiety after nutritional rehabilitation when possible
Complications
- Bradycardia/QT prolongation/sudden death:
- Refeeding syndrome:
- Amenorrhea/low bone density/fractures:
- Gastroparesis/constipation:
- Cytopenias:
- Suicide:
USMLE Step 2 CK Exam Tips
- 1Amenorrhea is not required
- 2Bradycardia in malnourished patient is red flag, not athletic conditioning
- 3Refeeding syndrome = low phosphate
- 4Adolescent best psychotherapy = family-based treatment
- 5No medication is first-line for weight restoration
- 6Low body weight distinguishes anorexia binge-purge subtype from bulimia
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